linux/fs/xattr.c

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// SPDX-License-Identifier: GPL-2.0-only
/*
File: fs/xattr.c
Extended attribute handling.
Copyright (C) 2001 by Andreas Gruenbacher <a.gruenbacher@computer.org>
Copyright (C) 2001 SGI - Silicon Graphics, Inc <linux-xfs@oss.sgi.com>
Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
*/
#include <linux/fs.h>
#include <linux/filelock.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/xattr.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/export.h>
#include <linux/fsnotify.h>
#include <linux/audit.h>
#include <linux/vmalloc.h>
2012-02-08 02:52:57 +00:00
#include <linux/posix_acl_xattr.h>
#include <linux/uaccess.h>
#include "internal.h"
static const char *
strcmp_prefix(const char *a, const char *a_prefix)
{
while (*a_prefix && *a == *a_prefix) {
a++;
a_prefix++;
}
return *a_prefix ? NULL : a;
}
/*
* In order to implement different sets of xattr operations for each xattr
* prefix, a filesystem should create a null-terminated array of struct
* xattr_handler (one for each prefix) and hang a pointer to it off of the
* s_xattr field of the superblock.
*/
#define for_each_xattr_handler(handlers, handler) \
if (handlers) \
for ((handler) = *(handlers)++; \
(handler) != NULL; \
(handler) = *(handlers)++)
/*
* Find the xattr_handler with the matching prefix.
*/
static const struct xattr_handler *
xattr_resolve_name(struct inode *inode, const char **name)
{
const struct xattr_handler * const *handlers = inode->i_sb->s_xattr;
const struct xattr_handler *handler;
if (!(inode->i_opflags & IOP_XATTR)) {
if (unlikely(is_bad_inode(inode)))
return ERR_PTR(-EIO);
return ERR_PTR(-EOPNOTSUPP);
}
for_each_xattr_handler(handlers, handler) {
const char *n;
n = strcmp_prefix(*name, xattr_prefix(handler));
if (n) {
if (!handler->prefix ^ !*n) {
if (*n)
continue;
return ERR_PTR(-EINVAL);
}
*name = n;
return handler;
}
}
return ERR_PTR(-EOPNOTSUPP);
}
/**
* may_write_xattr - check whether inode allows writing xattr
* @idmap: idmap of the mount the inode was found from
* @inode: the inode on which to set an xattr
*
* Check whether the inode allows writing xattrs. Specifically, we can never
* set or remove an extended attribute on a read-only filesystem or on an
* immutable / append-only inode.
*
* We also need to ensure that the inode has a mapping in the mount to
* not risk writing back invalid i_{g,u}id values.
*
* Return: On success zero is returned. On error a negative errno is returned.
*/
int may_write_xattr(struct mnt_idmap *idmap, struct inode *inode)
{
if (IS_IMMUTABLE(inode))
return -EPERM;
if (IS_APPEND(inode))
return -EPERM;
if (HAS_UNMAPPED_ID(idmap, inode))
return -EPERM;
return 0;
}
/*
* Check permissions for extended attribute access. This is a bit complicated
* because different namespaces have very different rules.
*/
static int
xattr_permission(struct mnt_idmap *idmap, struct inode *inode,
const char *name, int mask)
{
if (mask & MAY_WRITE) {
int ret;
ret = may_write_xattr(idmap, inode);
if (ret)
return ret;
}
/*
* No restriction for security.* and system.* from the VFS. Decision
* on these is left to the underlying filesystem / security module.
*/
if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN) ||
!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
return 0;
/*
* The trusted.* namespace can only be accessed by privileged users.
*/
if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN)) {
if (!capable(CAP_SYS_ADMIN))
return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
return 0;
}
/*
* In the user.* namespace, only regular files and directories can have
* extended attributes. For sticky directories, only the owner and
* privileged users can write attributes.
*/
if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
if (S_ISDIR(inode->i_mode) && (inode->i_mode & S_ISVTX) &&
(mask & MAY_WRITE) &&
!inode_owner_or_capable(idmap, inode))
return -EPERM;
}
return inode_permission(idmap, inode, mask);
}
/*
* Look for any handler that deals with the specified namespace.
*/
int
xattr_supports_user_prefix(struct inode *inode)
{
const struct xattr_handler * const *handlers = inode->i_sb->s_xattr;
const struct xattr_handler *handler;
if (!(inode->i_opflags & IOP_XATTR)) {
if (unlikely(is_bad_inode(inode)))
return -EIO;
return -EOPNOTSUPP;
}
for_each_xattr_handler(handlers, handler) {
if (!strncmp(xattr_prefix(handler), XATTR_USER_PREFIX,
XATTR_USER_PREFIX_LEN))
return 0;
}
return -EOPNOTSUPP;
}
EXPORT_SYMBOL(xattr_supports_user_prefix);
int
__vfs_setxattr(struct mnt_idmap *idmap, struct dentry *dentry,
struct inode *inode, const char *name, const void *value,
size_t size, int flags)
{
const struct xattr_handler *handler;
if (is_posix_acl_xattr(name))
return -EOPNOTSUPP;
handler = xattr_resolve_name(inode, &name);
if (IS_ERR(handler))
return PTR_ERR(handler);
if (!handler->set)
return -EOPNOTSUPP;
if (size == 0)
value = ""; /* empty EA, do not remove */
return handler->set(handler, idmap, dentry, inode, name, value,
acl: handle idmapped mounts The posix acl permission checking helpers determine whether a caller is privileged over an inode according to the acls associated with the inode. Add helpers that make it possible to handle acls on idmapped mounts. The vfs and the filesystems targeted by this first iteration make use of posix_acl_fix_xattr_from_user() and posix_acl_fix_xattr_to_user() to translate basic posix access and default permissions such as the ACL_USER and ACL_GROUP type according to the initial user namespace (or the superblock's user namespace) to and from the caller's current user namespace. Adapt these two helpers to handle idmapped mounts whereby we either map from or into the mount's user namespace depending on in which direction we're translating. Similarly, cap_convert_nscap() is used by the vfs to translate user namespace and non-user namespace aware filesystem capabilities from the superblock's user namespace to the caller's user namespace. Enable it to handle idmapped mounts by accounting for the mount's user namespace. In addition the fileystems targeted in the first iteration of this patch series make use of the posix_acl_chmod() and, posix_acl_update_mode() helpers. Both helpers perform permission checks on the target inode. Let them handle idmapped mounts. These two helpers are called when posix acls are set by the respective filesystems to handle this case we extend the ->set() method to take an additional user namespace argument to pass the mount's user namespace down. Link: https://lore.kernel.org/r/20210121131959.646623-9-christian.brauner@ubuntu.com Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-21 13:19:27 +00:00
size, flags);
}
EXPORT_SYMBOL(__vfs_setxattr);
/**
* __vfs_setxattr_noperm - perform setxattr operation without performing
* permission checks.
*
* @idmap: idmap of the mount the inode was found from
* @dentry: object to perform setxattr on
* @name: xattr name to set
* @value: value to set @name to
* @size: size of @value
* @flags: flags to pass into filesystem operations
*
* returns the result of the internal setxattr or setsecurity operations.
*
* This function requires the caller to lock the inode's i_mutex before it
* is executed. It also assumes that the caller will make the appropriate
* permission checks.
*/
int __vfs_setxattr_noperm(struct mnt_idmap *idmap,
struct dentry *dentry, const char *name,
const void *value, size_t size, int flags)
{
struct inode *inode = dentry->d_inode;
int error = -EAGAIN;
Cache xattr security drop check for write v2 Some recent benchmarking on btrfs showed that a major scaling bottleneck on large systems on btrfs is currently the xattr lookup on every write. Why xattr lookup on every write I hear you ask? write wants to drop suid and security related xattrs that could set o capabilities for executables. To do that it currently looks up security.capability on EVERY write (even for non executables) to decide whether to drop it or not. In btrfs this causes an additional tree walk, hitting some per file system locks and quite bad scalability. In a simple read workload on a 8S system I saw over 90% CPU time in spinlocks related to that. Chris Mason tells me this is also a problem in ext4, where it hits the global mbcache lock. This patch adds a simple per inode to avoid this problem. We only do the lookup once per file and then if there is no xattr cache the decision. All xattr changes clear the flag. I also used the same flag to avoid the suid check, although that one is pretty cheap. A file system can also set this flag when it creates the inode, if it has a cheap way to do so. This is done for some common file systems in followon patches. With this patch a major part of the lock contention disappears for btrfs. Some testing on smaller systems didn't show significant performance changes, but at least it helps the larger systems and is generally more efficient. v2: Rename is_sgid. add file system helper. Cc: chris.mason@oracle.com Cc: josef@redhat.com Cc: viro@zeniv.linux.org.uk Cc: agruen@linbit.com Cc: Serge E. Hallyn <serue@us.ibm.com> Signed-off-by: Andi Kleen <ak@linux.intel.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-28 15:25:51 +00:00
int issec = !strncmp(name, XATTR_SECURITY_PREFIX,
XATTR_SECURITY_PREFIX_LEN);
Cache xattr security drop check for write v2 Some recent benchmarking on btrfs showed that a major scaling bottleneck on large systems on btrfs is currently the xattr lookup on every write. Why xattr lookup on every write I hear you ask? write wants to drop suid and security related xattrs that could set o capabilities for executables. To do that it currently looks up security.capability on EVERY write (even for non executables) to decide whether to drop it or not. In btrfs this causes an additional tree walk, hitting some per file system locks and quite bad scalability. In a simple read workload on a 8S system I saw over 90% CPU time in spinlocks related to that. Chris Mason tells me this is also a problem in ext4, where it hits the global mbcache lock. This patch adds a simple per inode to avoid this problem. We only do the lookup once per file and then if there is no xattr cache the decision. All xattr changes clear the flag. I also used the same flag to avoid the suid check, although that one is pretty cheap. A file system can also set this flag when it creates the inode, if it has a cheap way to do so. This is done for some common file systems in followon patches. With this patch a major part of the lock contention disappears for btrfs. Some testing on smaller systems didn't show significant performance changes, but at least it helps the larger systems and is generally more efficient. v2: Rename is_sgid. add file system helper. Cc: chris.mason@oracle.com Cc: josef@redhat.com Cc: viro@zeniv.linux.org.uk Cc: agruen@linbit.com Cc: Serge E. Hallyn <serue@us.ibm.com> Signed-off-by: Andi Kleen <ak@linux.intel.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-28 15:25:51 +00:00
if (issec)
inode->i_flags &= ~S_NOSEC;
if (inode->i_opflags & IOP_XATTR) {
error = __vfs_setxattr(idmap, dentry, inode, name, value,
size, flags);
if (!error) {
fsnotify_xattr(dentry);
security_inode_post_setxattr(dentry, name, value,
size, flags);
}
} else {
if (unlikely(is_bad_inode(inode)))
return -EIO;
}
if (error == -EAGAIN) {
error = -EOPNOTSUPP;
if (issec) {
const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
error = security_inode_setsecurity(inode, suffix, value,
size, flags);
if (!error)
fsnotify_xattr(dentry);
}
}
return error;
}
/**
fs/xattr.c: fix kernel-doc warnings for setxattr & removexattr Fix kernel-doc warnings in fs/xattr.c: ../fs/xattr.c:251: warning: Function parameter or member 'dentry' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'name' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'value' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'size' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'flags' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'delegated_inode' not described in '__vfs_setxattr_locked' ../fs/xattr.c:458: warning: Function parameter or member 'dentry' not described in '__vfs_removexattr_locked' ../fs/xattr.c:458: warning: Function parameter or member 'name' not described in '__vfs_removexattr_locked' ../fs/xattr.c:458: warning: Function parameter or member 'delegated_inode' not described in '__vfs_removexattr_locked' Fixes: 08b5d5014a27 ("xattr: break delegations in {set,remove}xattr") Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Frank van der Linden <fllinden@amazon.com> Cc: Chuck Lever <chuck.lever@oracle.com> Link: http://lkml.kernel.org/r/7a3dd5a2-5787-adf3-d525-c203f9910ec4@infradead.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-13 23:48:27 +00:00
* __vfs_setxattr_locked - set an extended attribute while holding the inode
* lock
*
* @idmap: idmap of the mount of the target inode
fs/xattr.c: fix kernel-doc warnings for setxattr & removexattr Fix kernel-doc warnings in fs/xattr.c: ../fs/xattr.c:251: warning: Function parameter or member 'dentry' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'name' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'value' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'size' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'flags' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'delegated_inode' not described in '__vfs_setxattr_locked' ../fs/xattr.c:458: warning: Function parameter or member 'dentry' not described in '__vfs_removexattr_locked' ../fs/xattr.c:458: warning: Function parameter or member 'name' not described in '__vfs_removexattr_locked' ../fs/xattr.c:458: warning: Function parameter or member 'delegated_inode' not described in '__vfs_removexattr_locked' Fixes: 08b5d5014a27 ("xattr: break delegations in {set,remove}xattr") Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Frank van der Linden <fllinden@amazon.com> Cc: Chuck Lever <chuck.lever@oracle.com> Link: http://lkml.kernel.org/r/7a3dd5a2-5787-adf3-d525-c203f9910ec4@infradead.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-13 23:48:27 +00:00
* @dentry: object to perform setxattr on
* @name: xattr name to set
* @value: value to set @name to
* @size: size of @value
* @flags: flags to pass into filesystem operations
* @delegated_inode: on return, will contain an inode pointer that
* a delegation was broken on, NULL if none.
*/
int
__vfs_setxattr_locked(struct mnt_idmap *idmap, struct dentry *dentry,
const char *name, const void *value, size_t size,
int flags, struct inode **delegated_inode)
{
struct inode *inode = dentry->d_inode;
int error;
error = xattr_permission(idmap, inode, name, MAY_WRITE);
if (error)
return error;
error = security_inode_setxattr(idmap, dentry, name, value, size,
commoncap: handle idmapped mounts When interacting with user namespace and non-user namespace aware filesystem capabilities the vfs will perform various security checks to determine whether or not the filesystem capabilities can be used by the caller, whether they need to be removed and so on. The main infrastructure for this resides in the capability codepaths but they are called through the LSM security infrastructure even though they are not technically an LSM or optional. This extends the existing security hooks security_inode_removexattr(), security_inode_killpriv(), security_inode_getsecurity() to pass down the mount's user namespace and makes them aware of idmapped mounts. In order to actually get filesystem capabilities from disk the capability infrastructure exposes the get_vfs_caps_from_disk() helper. For user namespace aware filesystem capabilities a root uid is stored alongside the capabilities. In order to determine whether the caller can make use of the filesystem capability or whether it needs to be ignored it is translated according to the superblock's user namespace. If it can be translated to uid 0 according to that id mapping the caller can use the filesystem capabilities stored on disk. If we are accessing the inode that holds the filesystem capabilities through an idmapped mount we map the root uid according to the mount's user namespace. Afterwards the checks are identical to non-idmapped mounts: reading filesystem caps from disk enforces that the root uid associated with the filesystem capability must have a mapping in the superblock's user namespace and that the caller is either in the same user namespace or is a descendant of the superblock's user namespace. For filesystems that are mountable inside user namespace the caller can just mount the filesystem and won't usually need to idmap it. If they do want to idmap it they can create an idmapped mount and mark it with a user namespace they created and which is thus a descendant of s_user_ns. For filesystems that are not mountable inside user namespaces the descendant rule is trivially true because the s_user_ns will be the initial user namespace. If the initial user namespace is passed nothing changes so non-idmapped mounts will see identical behavior as before. Link: https://lore.kernel.org/r/20210121131959.646623-11-christian.brauner@ubuntu.com Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Reviewed-by: Christoph Hellwig <hch@lst.de> Acked-by: James Morris <jamorris@linux.microsoft.com> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-21 13:19:29 +00:00
flags);
if (error)
goto out;
error = try_break_deleg(inode, delegated_inode);
if (error)
goto out;
error = __vfs_setxattr_noperm(idmap, dentry, name, value,
size, flags);
out:
return error;
}
EXPORT_SYMBOL_GPL(__vfs_setxattr_locked);
int
vfs_setxattr(struct mnt_idmap *idmap, struct dentry *dentry,
const char *name, const void *value, size_t size, int flags)
{
struct inode *inode = dentry->d_inode;
struct inode *delegated_inode = NULL;
const void *orig_value = value;
int error;
if (size && strcmp(name, XATTR_NAME_CAPS) == 0) {
error = cap_convert_nscap(idmap, dentry, &value, size);
if (error < 0)
return error;
size = error;
}
retry_deleg:
inode_lock(inode);
error = __vfs_setxattr_locked(idmap, dentry, name, value, size,
flags, &delegated_inode);
inode_unlock(inode);
if (delegated_inode) {
error = break_deleg_wait(&delegated_inode);
if (!error)
goto retry_deleg;
}
if (value != orig_value)
kfree(value);
return error;
}
EXPORT_SYMBOL_GPL(vfs_setxattr);
static ssize_t
xattr_getsecurity(struct mnt_idmap *idmap, struct inode *inode,
commoncap: handle idmapped mounts When interacting with user namespace and non-user namespace aware filesystem capabilities the vfs will perform various security checks to determine whether or not the filesystem capabilities can be used by the caller, whether they need to be removed and so on. The main infrastructure for this resides in the capability codepaths but they are called through the LSM security infrastructure even though they are not technically an LSM or optional. This extends the existing security hooks security_inode_removexattr(), security_inode_killpriv(), security_inode_getsecurity() to pass down the mount's user namespace and makes them aware of idmapped mounts. In order to actually get filesystem capabilities from disk the capability infrastructure exposes the get_vfs_caps_from_disk() helper. For user namespace aware filesystem capabilities a root uid is stored alongside the capabilities. In order to determine whether the caller can make use of the filesystem capability or whether it needs to be ignored it is translated according to the superblock's user namespace. If it can be translated to uid 0 according to that id mapping the caller can use the filesystem capabilities stored on disk. If we are accessing the inode that holds the filesystem capabilities through an idmapped mount we map the root uid according to the mount's user namespace. Afterwards the checks are identical to non-idmapped mounts: reading filesystem caps from disk enforces that the root uid associated with the filesystem capability must have a mapping in the superblock's user namespace and that the caller is either in the same user namespace or is a descendant of the superblock's user namespace. For filesystems that are mountable inside user namespace the caller can just mount the filesystem and won't usually need to idmap it. If they do want to idmap it they can create an idmapped mount and mark it with a user namespace they created and which is thus a descendant of s_user_ns. For filesystems that are not mountable inside user namespaces the descendant rule is trivially true because the s_user_ns will be the initial user namespace. If the initial user namespace is passed nothing changes so non-idmapped mounts will see identical behavior as before. Link: https://lore.kernel.org/r/20210121131959.646623-11-christian.brauner@ubuntu.com Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Reviewed-by: Christoph Hellwig <hch@lst.de> Acked-by: James Morris <jamorris@linux.microsoft.com> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-21 13:19:29 +00:00
const char *name, void *value, size_t size)
{
void *buffer = NULL;
ssize_t len;
if (!value || !size) {
len = security_inode_getsecurity(idmap, inode, name,
commoncap: handle idmapped mounts When interacting with user namespace and non-user namespace aware filesystem capabilities the vfs will perform various security checks to determine whether or not the filesystem capabilities can be used by the caller, whether they need to be removed and so on. The main infrastructure for this resides in the capability codepaths but they are called through the LSM security infrastructure even though they are not technically an LSM or optional. This extends the existing security hooks security_inode_removexattr(), security_inode_killpriv(), security_inode_getsecurity() to pass down the mount's user namespace and makes them aware of idmapped mounts. In order to actually get filesystem capabilities from disk the capability infrastructure exposes the get_vfs_caps_from_disk() helper. For user namespace aware filesystem capabilities a root uid is stored alongside the capabilities. In order to determine whether the caller can make use of the filesystem capability or whether it needs to be ignored it is translated according to the superblock's user namespace. If it can be translated to uid 0 according to that id mapping the caller can use the filesystem capabilities stored on disk. If we are accessing the inode that holds the filesystem capabilities through an idmapped mount we map the root uid according to the mount's user namespace. Afterwards the checks are identical to non-idmapped mounts: reading filesystem caps from disk enforces that the root uid associated with the filesystem capability must have a mapping in the superblock's user namespace and that the caller is either in the same user namespace or is a descendant of the superblock's user namespace. For filesystems that are mountable inside user namespace the caller can just mount the filesystem and won't usually need to idmap it. If they do want to idmap it they can create an idmapped mount and mark it with a user namespace they created and which is thus a descendant of s_user_ns. For filesystems that are not mountable inside user namespaces the descendant rule is trivially true because the s_user_ns will be the initial user namespace. If the initial user namespace is passed nothing changes so non-idmapped mounts will see identical behavior as before. Link: https://lore.kernel.org/r/20210121131959.646623-11-christian.brauner@ubuntu.com Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Reviewed-by: Christoph Hellwig <hch@lst.de> Acked-by: James Morris <jamorris@linux.microsoft.com> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-21 13:19:29 +00:00
&buffer, false);
goto out_noalloc;
}
len = security_inode_getsecurity(idmap, inode, name, &buffer,
commoncap: handle idmapped mounts When interacting with user namespace and non-user namespace aware filesystem capabilities the vfs will perform various security checks to determine whether or not the filesystem capabilities can be used by the caller, whether they need to be removed and so on. The main infrastructure for this resides in the capability codepaths but they are called through the LSM security infrastructure even though they are not technically an LSM or optional. This extends the existing security hooks security_inode_removexattr(), security_inode_killpriv(), security_inode_getsecurity() to pass down the mount's user namespace and makes them aware of idmapped mounts. In order to actually get filesystem capabilities from disk the capability infrastructure exposes the get_vfs_caps_from_disk() helper. For user namespace aware filesystem capabilities a root uid is stored alongside the capabilities. In order to determine whether the caller can make use of the filesystem capability or whether it needs to be ignored it is translated according to the superblock's user namespace. If it can be translated to uid 0 according to that id mapping the caller can use the filesystem capabilities stored on disk. If we are accessing the inode that holds the filesystem capabilities through an idmapped mount we map the root uid according to the mount's user namespace. Afterwards the checks are identical to non-idmapped mounts: reading filesystem caps from disk enforces that the root uid associated with the filesystem capability must have a mapping in the superblock's user namespace and that the caller is either in the same user namespace or is a descendant of the superblock's user namespace. For filesystems that are mountable inside user namespace the caller can just mount the filesystem and won't usually need to idmap it. If they do want to idmap it they can create an idmapped mount and mark it with a user namespace they created and which is thus a descendant of s_user_ns. For filesystems that are not mountable inside user namespaces the descendant rule is trivially true because the s_user_ns will be the initial user namespace. If the initial user namespace is passed nothing changes so non-idmapped mounts will see identical behavior as before. Link: https://lore.kernel.org/r/20210121131959.646623-11-christian.brauner@ubuntu.com Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Reviewed-by: Christoph Hellwig <hch@lst.de> Acked-by: James Morris <jamorris@linux.microsoft.com> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-21 13:19:29 +00:00
true);
if (len < 0)
return len;
if (size < len) {
len = -ERANGE;
goto out;
}
memcpy(value, buffer, len);
out:
kfree(buffer);
out_noalloc:
return len;
}
/*
* vfs_getxattr_alloc - allocate memory, if necessary, before calling getxattr
*
* Allocate memory, if not already allocated, or re-allocate correct size,
* before retrieving the extended attribute. The xattr value buffer should
* always be freed by the caller, even on error.
*
* Returns the result of alloc, if failed, or the getxattr operation.
*/
int
vfs_getxattr_alloc(struct mnt_idmap *idmap, struct dentry *dentry,
const char *name, char **xattr_value, size_t xattr_size,
gfp_t flags)
{
const struct xattr_handler *handler;
struct inode *inode = dentry->d_inode;
char *value = *xattr_value;
int error;
error = xattr_permission(idmap, inode, name, MAY_READ);
if (error)
return error;
handler = xattr_resolve_name(inode, &name);
if (IS_ERR(handler))
return PTR_ERR(handler);
if (!handler->get)
return -EOPNOTSUPP;
error = handler->get(handler, dentry, inode, name, NULL, 0);
if (error < 0)
return error;
if (!value || (error > xattr_size)) {
value = krealloc(*xattr_value, error + 1, flags);
if (!value)
return -ENOMEM;
memset(value, 0, error + 1);
}
error = handler->get(handler, dentry, inode, name, value, error);
*xattr_value = value;
return error;
}
ssize_t
__vfs_getxattr(struct dentry *dentry, struct inode *inode, const char *name,
void *value, size_t size)
{
const struct xattr_handler *handler;
if (is_posix_acl_xattr(name))
return -EOPNOTSUPP;
handler = xattr_resolve_name(inode, &name);
if (IS_ERR(handler))
return PTR_ERR(handler);
if (!handler->get)
return -EOPNOTSUPP;
return handler->get(handler, dentry, inode, name, value, size);
}
EXPORT_SYMBOL(__vfs_getxattr);
ssize_t
vfs_getxattr(struct mnt_idmap *idmap, struct dentry *dentry,
const char *name, void *value, size_t size)
{
struct inode *inode = dentry->d_inode;
int error;
error = xattr_permission(idmap, inode, name, MAY_READ);
if (error)
return error;
error = security_inode_getxattr(dentry, name);
if (error)
return error;
if (!strncmp(name, XATTR_SECURITY_PREFIX,
XATTR_SECURITY_PREFIX_LEN)) {
const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
int ret = xattr_getsecurity(idmap, inode, suffix, value,
commoncap: handle idmapped mounts When interacting with user namespace and non-user namespace aware filesystem capabilities the vfs will perform various security checks to determine whether or not the filesystem capabilities can be used by the caller, whether they need to be removed and so on. The main infrastructure for this resides in the capability codepaths but they are called through the LSM security infrastructure even though they are not technically an LSM or optional. This extends the existing security hooks security_inode_removexattr(), security_inode_killpriv(), security_inode_getsecurity() to pass down the mount's user namespace and makes them aware of idmapped mounts. In order to actually get filesystem capabilities from disk the capability infrastructure exposes the get_vfs_caps_from_disk() helper. For user namespace aware filesystem capabilities a root uid is stored alongside the capabilities. In order to determine whether the caller can make use of the filesystem capability or whether it needs to be ignored it is translated according to the superblock's user namespace. If it can be translated to uid 0 according to that id mapping the caller can use the filesystem capabilities stored on disk. If we are accessing the inode that holds the filesystem capabilities through an idmapped mount we map the root uid according to the mount's user namespace. Afterwards the checks are identical to non-idmapped mounts: reading filesystem caps from disk enforces that the root uid associated with the filesystem capability must have a mapping in the superblock's user namespace and that the caller is either in the same user namespace or is a descendant of the superblock's user namespace. For filesystems that are mountable inside user namespace the caller can just mount the filesystem and won't usually need to idmap it. If they do want to idmap it they can create an idmapped mount and mark it with a user namespace they created and which is thus a descendant of s_user_ns. For filesystems that are not mountable inside user namespaces the descendant rule is trivially true because the s_user_ns will be the initial user namespace. If the initial user namespace is passed nothing changes so non-idmapped mounts will see identical behavior as before. Link: https://lore.kernel.org/r/20210121131959.646623-11-christian.brauner@ubuntu.com Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Reviewed-by: Christoph Hellwig <hch@lst.de> Acked-by: James Morris <jamorris@linux.microsoft.com> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-21 13:19:29 +00:00
size);
/*
* Only overwrite the return value if a security module
* is actually active.
*/
if (ret == -EOPNOTSUPP)
goto nolsm;
return ret;
}
nolsm:
return __vfs_getxattr(dentry, inode, name, value, size);
}
EXPORT_SYMBOL_GPL(vfs_getxattr);
/**
* vfs_listxattr - retrieve \0 separated list of xattr names
* @dentry: the dentry from whose inode the xattr names are retrieved
* @list: buffer to store xattr names into
* @size: size of the buffer
*
* This function returns the names of all xattrs associated with the
* inode of @dentry.
*
* Note, for legacy reasons the vfs_listxattr() function lists POSIX
* ACLs as well. Since POSIX ACLs are decoupled from IOP_XATTR the
* vfs_listxattr() function doesn't check for this flag since a
* filesystem could implement POSIX ACLs without implementing any other
* xattrs.
*
* However, since all codepaths that remove IOP_XATTR also assign of
* inode operations that either don't implement or implement a stub
* ->listxattr() operation.
*
* Return: On success, the size of the buffer that was used. On error a
* negative error code.
*/
ssize_t
vfs_listxattr(struct dentry *dentry, char *list, size_t size)
{
struct inode *inode = d_inode(dentry);
ssize_t error;
error = security_inode_listxattr(dentry);
if (error)
return error;
if (inode->i_op->listxattr) {
error = inode->i_op->listxattr(dentry, list, size);
} else {
error = security_inode_listsecurity(inode, list, size);
if (size && error > size)
error = -ERANGE;
}
return error;
}
EXPORT_SYMBOL_GPL(vfs_listxattr);
int
__vfs_removexattr(struct mnt_idmap *idmap, struct dentry *dentry,
const char *name)
{
struct inode *inode = d_inode(dentry);
const struct xattr_handler *handler;
if (is_posix_acl_xattr(name))
return -EOPNOTSUPP;
handler = xattr_resolve_name(inode, &name);
if (IS_ERR(handler))
return PTR_ERR(handler);
if (!handler->set)
return -EOPNOTSUPP;
return handler->set(handler, idmap, dentry, inode, name, NULL, 0,
XATTR_REPLACE);
}
EXPORT_SYMBOL(__vfs_removexattr);
/**
fs/xattr.c: fix kernel-doc warnings for setxattr & removexattr Fix kernel-doc warnings in fs/xattr.c: ../fs/xattr.c:251: warning: Function parameter or member 'dentry' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'name' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'value' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'size' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'flags' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'delegated_inode' not described in '__vfs_setxattr_locked' ../fs/xattr.c:458: warning: Function parameter or member 'dentry' not described in '__vfs_removexattr_locked' ../fs/xattr.c:458: warning: Function parameter or member 'name' not described in '__vfs_removexattr_locked' ../fs/xattr.c:458: warning: Function parameter or member 'delegated_inode' not described in '__vfs_removexattr_locked' Fixes: 08b5d5014a27 ("xattr: break delegations in {set,remove}xattr") Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Frank van der Linden <fllinden@amazon.com> Cc: Chuck Lever <chuck.lever@oracle.com> Link: http://lkml.kernel.org/r/7a3dd5a2-5787-adf3-d525-c203f9910ec4@infradead.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-13 23:48:27 +00:00
* __vfs_removexattr_locked - set an extended attribute while holding the inode
* lock
*
* @idmap: idmap of the mount of the target inode
fs/xattr.c: fix kernel-doc warnings for setxattr & removexattr Fix kernel-doc warnings in fs/xattr.c: ../fs/xattr.c:251: warning: Function parameter or member 'dentry' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'name' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'value' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'size' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'flags' not described in '__vfs_setxattr_locked' ../fs/xattr.c:251: warning: Function parameter or member 'delegated_inode' not described in '__vfs_setxattr_locked' ../fs/xattr.c:458: warning: Function parameter or member 'dentry' not described in '__vfs_removexattr_locked' ../fs/xattr.c:458: warning: Function parameter or member 'name' not described in '__vfs_removexattr_locked' ../fs/xattr.c:458: warning: Function parameter or member 'delegated_inode' not described in '__vfs_removexattr_locked' Fixes: 08b5d5014a27 ("xattr: break delegations in {set,remove}xattr") Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Frank van der Linden <fllinden@amazon.com> Cc: Chuck Lever <chuck.lever@oracle.com> Link: http://lkml.kernel.org/r/7a3dd5a2-5787-adf3-d525-c203f9910ec4@infradead.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-13 23:48:27 +00:00
* @dentry: object to perform setxattr on
* @name: name of xattr to remove
* @delegated_inode: on return, will contain an inode pointer that
* a delegation was broken on, NULL if none.
*/
int
__vfs_removexattr_locked(struct mnt_idmap *idmap,
struct dentry *dentry, const char *name,
struct inode **delegated_inode)
{
struct inode *inode = dentry->d_inode;
int error;
error = xattr_permission(idmap, inode, name, MAY_WRITE);
if (error)
return error;
error = security_inode_removexattr(idmap, dentry, name);
if (error)
goto out;
error = try_break_deleg(inode, delegated_inode);
if (error)
goto out;
error = __vfs_removexattr(idmap, dentry, name);
if (error)
return error;
fsnotify_xattr(dentry);
security_inode_post_removexattr(dentry, name);
out:
return error;
}
EXPORT_SYMBOL_GPL(__vfs_removexattr_locked);
int
vfs_removexattr(struct mnt_idmap *idmap, struct dentry *dentry,
const char *name)
{
struct inode *inode = dentry->d_inode;
struct inode *delegated_inode = NULL;
int error;
retry_deleg:
inode_lock(inode);
error = __vfs_removexattr_locked(idmap, dentry,
name, &delegated_inode);
inode_unlock(inode);
if (delegated_inode) {
error = break_deleg_wait(&delegated_inode);
if (!error)
goto retry_deleg;
}
return error;
}
EXPORT_SYMBOL_GPL(vfs_removexattr);
/*
* Extended attribute SET operations
*/
int setxattr_copy(const char __user *name, struct xattr_ctx *ctx)
{
int error;
if (ctx->flags & ~(XATTR_CREATE|XATTR_REPLACE))
return -EINVAL;
error = strncpy_from_user(ctx->kname->name, name,
sizeof(ctx->kname->name));
if (error == 0 || error == sizeof(ctx->kname->name))
return -ERANGE;
if (error < 0)
return error;
error = 0;
if (ctx->size) {
if (ctx->size > XATTR_SIZE_MAX)
return -E2BIG;
ctx->kvalue = vmemdup_user(ctx->cvalue, ctx->size);
if (IS_ERR(ctx->kvalue)) {
error = PTR_ERR(ctx->kvalue);
ctx->kvalue = NULL;
}
}
return error;
}
int do_setxattr(struct mnt_idmap *idmap, struct dentry *dentry,
struct xattr_ctx *ctx)
{
if (is_posix_acl_xattr(ctx->kname->name))
return do_set_acl(idmap, dentry, ctx->kname->name,
ctx->kvalue, ctx->size);
return vfs_setxattr(idmap, dentry, ctx->kname->name,
ctx->kvalue, ctx->size, ctx->flags);
}
static long
setxattr(struct mnt_idmap *idmap, struct dentry *d,
const char __user *name, const void __user *value, size_t size,
int flags)
{
struct xattr_name kname;
struct xattr_ctx ctx = {
.cvalue = value,
.kvalue = NULL,
.size = size,
.kname = &kname,
.flags = flags,
};
int error;
error = setxattr_copy(name, &ctx);
if (error)
return error;
error = do_setxattr(idmap, d, &ctx);
kvfree(ctx.kvalue);
return error;
}
static int path_setxattr(const char __user *pathname,
const char __user *name, const void __user *value,
size_t size, int flags, unsigned int lookup_flags)
{
struct path path;
int error;
retry:
error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
if (error)
return error;
error = mnt_want_write(path.mnt);
if (!error) {
error = setxattr(mnt_idmap(path.mnt), path.dentry, name,
value, size, flags);
mnt_drop_write(path.mnt);
}
path_put(&path);
if (retry_estale(error, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;
goto retry;
}
return error;
}
SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
const char __user *, name, const void __user *, value,
size_t, size, int, flags)
{
return path_setxattr(pathname, name, value, size, flags, LOOKUP_FOLLOW);
}
SYSCALL_DEFINE5(lsetxattr, const char __user *, pathname,
const char __user *, name, const void __user *, value,
size_t, size, int, flags)
{
return path_setxattr(pathname, name, value, size, flags, 0);
}
SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
const void __user *,value, size_t, size, int, flags)
{
struct fd f = fdget(fd);
int error = -EBADF;
if (!f.file)
return error;
audit_file(f.file);
error = mnt_want_write_file(f.file);
if (!error) {
error = setxattr(file_mnt_idmap(f.file),
f.file->f_path.dentry, name,
value, size, flags);
mnt_drop_write_file(f.file);
}
fdput(f);
return error;
}
/*
* Extended attribute GET operations
*/
ssize_t
do_getxattr(struct mnt_idmap *idmap, struct dentry *d,
struct xattr_ctx *ctx)
{
ssize_t error;
char *kname = ctx->kname->name;
if (ctx->size) {
if (ctx->size > XATTR_SIZE_MAX)
ctx->size = XATTR_SIZE_MAX;
ctx->kvalue = kvzalloc(ctx->size, GFP_KERNEL);
if (!ctx->kvalue)
treewide: use kv[mz]alloc* rather than opencoded variants There are many code paths opencoding kvmalloc. Let's use the helper instead. The main difference to kvmalloc is that those users are usually not considering all the aspects of the memory allocator. E.g. allocation requests <= 32kB (with 4kB pages) are basically never failing and invoke OOM killer to satisfy the allocation. This sounds too disruptive for something that has a reasonable fallback - the vmalloc. On the other hand those requests might fallback to vmalloc even when the memory allocator would succeed after several more reclaim/compaction attempts previously. There is no guarantee something like that happens though. This patch converts many of those places to kv[mz]alloc* helpers because they are more conservative. Link: http://lkml.kernel.org/r/20170306103327.2766-2-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> # Xen bits Acked-by: Kees Cook <keescook@chromium.org> Acked-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Andreas Dilger <andreas.dilger@intel.com> # Lustre Acked-by: Christian Borntraeger <borntraeger@de.ibm.com> # KVM/s390 Acked-by: Dan Williams <dan.j.williams@intel.com> # nvdim Acked-by: David Sterba <dsterba@suse.com> # btrfs Acked-by: Ilya Dryomov <idryomov@gmail.com> # Ceph Acked-by: Tariq Toukan <tariqt@mellanox.com> # mlx4 Acked-by: Leon Romanovsky <leonro@mellanox.com> # mlx5 Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: Anton Vorontsov <anton@enomsg.org> Cc: Colin Cross <ccross@android.com> Cc: Tony Luck <tony.luck@intel.com> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: Ben Skeggs <bskeggs@redhat.com> Cc: Kent Overstreet <kent.overstreet@gmail.com> Cc: Santosh Raspatur <santosh@chelsio.com> Cc: Hariprasad S <hariprasad@chelsio.com> Cc: Yishai Hadas <yishaih@mellanox.com> Cc: Oleg Drokin <oleg.drokin@intel.com> Cc: "Yan, Zheng" <zyan@redhat.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: David Miller <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-05-08 22:57:27 +00:00
return -ENOMEM;
}
if (is_posix_acl_xattr(ctx->kname->name))
error = do_get_acl(idmap, d, kname, ctx->kvalue, ctx->size);
else
error = vfs_getxattr(idmap, d, kname, ctx->kvalue, ctx->size);
if (error > 0) {
if (ctx->size && copy_to_user(ctx->value, ctx->kvalue, error))
error = -EFAULT;
} else if (error == -ERANGE && ctx->size >= XATTR_SIZE_MAX) {
/* The file system tried to returned a value bigger
than XATTR_SIZE_MAX bytes. Not possible. */
error = -E2BIG;
}
return error;
}
static ssize_t
getxattr(struct mnt_idmap *idmap, struct dentry *d,
const char __user *name, void __user *value, size_t size)
{
ssize_t error;
struct xattr_name kname;
struct xattr_ctx ctx = {
.value = value,
.kvalue = NULL,
.size = size,
.kname = &kname,
.flags = 0,
};
error = strncpy_from_user(kname.name, name, sizeof(kname.name));
if (error == 0 || error == sizeof(kname.name))
error = -ERANGE;
if (error < 0)
return error;
error = do_getxattr(idmap, d, &ctx);
kvfree(ctx.kvalue);
return error;
}
static ssize_t path_getxattr(const char __user *pathname,
const char __user *name, void __user *value,
size_t size, unsigned int lookup_flags)
{
struct path path;
ssize_t error;
retry:
error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
if (error)
return error;
error = getxattr(mnt_idmap(path.mnt), path.dentry, name, value, size);
path_put(&path);
if (retry_estale(error, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;
goto retry;
}
return error;
}
SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
const char __user *, name, void __user *, value, size_t, size)
{
return path_getxattr(pathname, name, value, size, LOOKUP_FOLLOW);
}
SYSCALL_DEFINE4(lgetxattr, const char __user *, pathname,
const char __user *, name, void __user *, value, size_t, size)
{
return path_getxattr(pathname, name, value, size, 0);
}
SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
void __user *, value, size_t, size)
{
struct fd f = fdget(fd);
ssize_t error = -EBADF;
if (!f.file)
return error;
audit_file(f.file);
error = getxattr(file_mnt_idmap(f.file), f.file->f_path.dentry,
name, value, size);
fdput(f);
return error;
}
/*
* Extended attribute LIST operations
*/
static ssize_t
listxattr(struct dentry *d, char __user *list, size_t size)
{
ssize_t error;
char *klist = NULL;
if (size) {
if (size > XATTR_LIST_MAX)
size = XATTR_LIST_MAX;
treewide: use kv[mz]alloc* rather than opencoded variants There are many code paths opencoding kvmalloc. Let's use the helper instead. The main difference to kvmalloc is that those users are usually not considering all the aspects of the memory allocator. E.g. allocation requests <= 32kB (with 4kB pages) are basically never failing and invoke OOM killer to satisfy the allocation. This sounds too disruptive for something that has a reasonable fallback - the vmalloc. On the other hand those requests might fallback to vmalloc even when the memory allocator would succeed after several more reclaim/compaction attempts previously. There is no guarantee something like that happens though. This patch converts many of those places to kv[mz]alloc* helpers because they are more conservative. Link: http://lkml.kernel.org/r/20170306103327.2766-2-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> # Xen bits Acked-by: Kees Cook <keescook@chromium.org> Acked-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Andreas Dilger <andreas.dilger@intel.com> # Lustre Acked-by: Christian Borntraeger <borntraeger@de.ibm.com> # KVM/s390 Acked-by: Dan Williams <dan.j.williams@intel.com> # nvdim Acked-by: David Sterba <dsterba@suse.com> # btrfs Acked-by: Ilya Dryomov <idryomov@gmail.com> # Ceph Acked-by: Tariq Toukan <tariqt@mellanox.com> # mlx4 Acked-by: Leon Romanovsky <leonro@mellanox.com> # mlx5 Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: Anton Vorontsov <anton@enomsg.org> Cc: Colin Cross <ccross@android.com> Cc: Tony Luck <tony.luck@intel.com> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: Ben Skeggs <bskeggs@redhat.com> Cc: Kent Overstreet <kent.overstreet@gmail.com> Cc: Santosh Raspatur <santosh@chelsio.com> Cc: Hariprasad S <hariprasad@chelsio.com> Cc: Yishai Hadas <yishaih@mellanox.com> Cc: Oleg Drokin <oleg.drokin@intel.com> Cc: "Yan, Zheng" <zyan@redhat.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: David Miller <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-05-08 22:57:27 +00:00
klist = kvmalloc(size, GFP_KERNEL);
if (!klist)
return -ENOMEM;
}
error = vfs_listxattr(d, klist, size);
if (error > 0) {
if (size && copy_to_user(list, klist, error))
error = -EFAULT;
} else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
/* The file system tried to returned a list bigger
than XATTR_LIST_MAX bytes. Not possible. */
error = -E2BIG;
}
kvfree(klist);
return error;
}
static ssize_t path_listxattr(const char __user *pathname, char __user *list,
size_t size, unsigned int lookup_flags)
{
struct path path;
ssize_t error;
retry:
error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
if (error)
return error;
error = listxattr(path.dentry, list, size);
path_put(&path);
if (retry_estale(error, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;
goto retry;
}
return error;
}
SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
size_t, size)
{
return path_listxattr(pathname, list, size, LOOKUP_FOLLOW);
}
SYSCALL_DEFINE3(llistxattr, const char __user *, pathname, char __user *, list,
size_t, size)
{
return path_listxattr(pathname, list, size, 0);
}
SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)
{
struct fd f = fdget(fd);
ssize_t error = -EBADF;
if (!f.file)
return error;
audit_file(f.file);
error = listxattr(f.file->f_path.dentry, list, size);
fdput(f);
return error;
}
/*
* Extended attribute REMOVE operations
*/
static long
removexattr(struct mnt_idmap *idmap, struct dentry *d,
const char __user *name)
{
int error;
char kname[XATTR_NAME_MAX + 1];
error = strncpy_from_user(kname, name, sizeof(kname));
if (error == 0 || error == sizeof(kname))
error = -ERANGE;
if (error < 0)
return error;
if (is_posix_acl_xattr(kname))
return vfs_remove_acl(idmap, d, kname);
return vfs_removexattr(idmap, d, kname);
}
static int path_removexattr(const char __user *pathname,
const char __user *name, unsigned int lookup_flags)
{
struct path path;
int error;
retry:
error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
if (error)
return error;
error = mnt_want_write(path.mnt);
if (!error) {
error = removexattr(mnt_idmap(path.mnt), path.dentry, name);
mnt_drop_write(path.mnt);
}
path_put(&path);
if (retry_estale(error, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;
goto retry;
}
return error;
}
SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
const char __user *, name)
{
return path_removexattr(pathname, name, LOOKUP_FOLLOW);
}
SYSCALL_DEFINE2(lremovexattr, const char __user *, pathname,
const char __user *, name)
{
return path_removexattr(pathname, name, 0);
}
SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)
{
struct fd f = fdget(fd);
int error = -EBADF;
if (!f.file)
return error;
audit_file(f.file);
error = mnt_want_write_file(f.file);
if (!error) {
error = removexattr(file_mnt_idmap(f.file),
f.file->f_path.dentry, name);
mnt_drop_write_file(f.file);
}
fdput(f);
return error;
}
int xattr_list_one(char **buffer, ssize_t *remaining_size, const char *name)
{
size_t len;
len = strlen(name) + 1;
if (*buffer) {
if (*remaining_size < len)
return -ERANGE;
memcpy(*buffer, name, len);
*buffer += len;
}
*remaining_size -= len;
return 0;
}
/**
* generic_listxattr - run through a dentry's xattr list() operations
* @dentry: dentry to list the xattrs
* @buffer: result buffer
* @buffer_size: size of @buffer
*
* Combine the results of the list() operation from every xattr_handler in the
* xattr_handler stack.
*
* Note that this will not include the entries for POSIX ACLs.
*/
ssize_t
generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
{
const struct xattr_handler *handler, * const *handlers = dentry->d_sb->s_xattr;
ssize_t remaining_size = buffer_size;
int err = 0;
for_each_xattr_handler(handlers, handler) {
if (!handler->name || (handler->list && !handler->list(dentry)))
continue;
err = xattr_list_one(&buffer, &remaining_size, handler->name);
if (err)
return err;
}
return err ? err : buffer_size - remaining_size;
}
EXPORT_SYMBOL(generic_listxattr);
/**
* xattr_full_name - Compute full attribute name from suffix
*
* @handler: handler of the xattr_handler operation
* @name: name passed to the xattr_handler operation
*
* The get and set xattr handler operations are called with the remainder of
* the attribute name after skipping the handler's prefix: for example, "foo"
* is passed to the get operation of a handler with prefix "user." to get
* attribute "user.foo". The full name is still "there" in the name though.
*
* Note: the list xattr handler operation when called from the vfs is passed a
* NULL name; some file systems use this operation internally, with varying
* semantics.
*/
const char *xattr_full_name(const struct xattr_handler *handler,
const char *name)
{
size_t prefix_len = strlen(xattr_prefix(handler));
return name - prefix_len;
}
EXPORT_SYMBOL(xattr_full_name);
tmpfs,xattr: enable limited user extended attributes Enable "user." extended attributes on tmpfs, limiting them by tracking the space they occupy, and deducting that space from the limited ispace (unless tmpfs mounted with nr_inodes=0 to leave that ispace unlimited). tmpfs inodes and simple xattrs are both unswappable, and have to be in lowmem on a 32-bit highmem kernel: so the ispace limit is appropriate for xattrs, without any need for a further mount option. Add simple_xattr_space() to give approximate but deterministic estimate of the space taken up by each xattr: with simple_xattrs_free() outputting the space freed if required (but kernfs and even some tmpfs usages do not require that, so don't waste time on strlen'ing if not needed). Security and trusted xattrs were already supported: for consistency and simplicity, account them from the same pool; though there's a small risk that a tmpfs with enough space before would now be considered too small. When extended attributes are used, "df -i" does show more IUsed and less IFree than can be explained by the inodes: document that (manpage later). xfstests tests/generic which were not run on tmpfs before but now pass: 020 037 062 070 077 097 103 117 337 377 454 486 523 533 611 618 728 with no new failures. Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com> Message-Id: <2e63b26e-df46-5baa-c7d6-f9a8dd3282c5@google.com> Signed-off-by: Christian Brauner <brauner@kernel.org>
2023-08-09 04:33:56 +00:00
/**
* simple_xattr_space - estimate the memory used by a simple xattr
* @name: the full name of the xattr
* @size: the size of its value
*
* This takes no account of how much larger the two slab objects actually are:
* that would depend on the slab implementation, when what is required is a
* deterministic number, which grows with name length and size and quantity.
*
* Return: The approximate number of bytes of memory used by such an xattr.
*/
size_t simple_xattr_space(const char *name, size_t size)
{
/*
* Use "40" instead of sizeof(struct simple_xattr), to return the
* same result on 32-bit and 64-bit, and even if simple_xattr grows.
*/
return 40 + size + strlen(name);
}
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
/**
* simple_xattr_free - free an xattr object
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
* @xattr: the xattr object
*
* Free the xattr object. Can handle @xattr being NULL.
*/
void simple_xattr_free(struct simple_xattr *xattr)
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
{
if (xattr)
kfree(xattr->name);
kvfree(xattr);
}
/**
* simple_xattr_alloc - allocate new xattr object
* @value: value of the xattr object
* @size: size of @value
*
* Allocate a new xattr object and initialize respective members. The caller is
* responsible for handling the name of the xattr.
*
* Return: On success a new xattr object is returned. On failure NULL is
* returned.
*/
struct simple_xattr *simple_xattr_alloc(const void *value, size_t size)
{
struct simple_xattr *new_xattr;
size_t len;
/* wrap around? */
len = sizeof(*new_xattr) + size;
if (len < sizeof(*new_xattr))
return NULL;
new_xattr = kvmalloc(len, GFP_KERNEL_ACCOUNT);
if (!new_xattr)
return NULL;
new_xattr->size = size;
memcpy(new_xattr->value, value, size);
return new_xattr;
}
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
/**
* rbtree_simple_xattr_cmp - compare xattr name with current rbtree xattr entry
* @key: xattr name
* @node: current node
*
* Compare the xattr name with the xattr name attached to @node in the rbtree.
*
* Return: Negative value if continuing left, positive if continuing right, 0
* if the xattr attached to @node matches @key.
*/
static int rbtree_simple_xattr_cmp(const void *key, const struct rb_node *node)
{
const char *xattr_name = key;
const struct simple_xattr *xattr;
xattr = rb_entry(node, struct simple_xattr, rb_node);
return strcmp(xattr->name, xattr_name);
}
/**
* rbtree_simple_xattr_node_cmp - compare two xattr rbtree nodes
* @new_node: new node
* @node: current node
*
* Compare the xattr attached to @new_node with the xattr attached to @node.
*
* Return: Negative value if continuing left, positive if continuing right, 0
* if the xattr attached to @new_node matches the xattr attached to @node.
*/
static int rbtree_simple_xattr_node_cmp(struct rb_node *new_node,
const struct rb_node *node)
{
struct simple_xattr *xattr;
xattr = rb_entry(new_node, struct simple_xattr, rb_node);
return rbtree_simple_xattr_cmp(xattr->name, node);
}
/**
* simple_xattr_get - get an xattr object
* @xattrs: the header of the xattr object
* @name: the name of the xattr to retrieve
* @buffer: the buffer to store the value into
* @size: the size of @buffer
*
* Try to find and retrieve the xattr object associated with @name.
* If @buffer is provided store the value of @xattr in @buffer
* otherwise just return the length. The size of @buffer is limited
* to XATTR_SIZE_MAX which currently is 65536.
*
* Return: On success the length of the xattr value is returned. On error a
* negative error code is returned.
*/
int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
void *buffer, size_t size)
{
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
struct simple_xattr *xattr = NULL;
struct rb_node *rbp;
int ret = -ENODATA;
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
read_lock(&xattrs->lock);
rbp = rb_find(name, &xattrs->rb_root, rbtree_simple_xattr_cmp);
if (rbp) {
xattr = rb_entry(rbp, struct simple_xattr, rb_node);
ret = xattr->size;
if (buffer) {
if (size < xattr->size)
ret = -ERANGE;
else
memcpy(buffer, xattr->value, xattr->size);
}
}
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
read_unlock(&xattrs->lock);
return ret;
}
/**
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
* simple_xattr_set - set an xattr object
* @xattrs: the header of the xattr object
* @name: the name of the xattr to retrieve
* @value: the value to store along the xattr
* @size: the size of @value
* @flags: the flags determining how to set the xattr
*
* Set a new xattr object.
* If @value is passed a new xattr object will be allocated. If XATTR_REPLACE
* is specified in @flags a matching xattr object for @name must already exist.
* If it does it will be replaced with the new xattr object. If it doesn't we
* fail. If XATTR_CREATE is specified and a matching xattr does already exist
* we fail. If it doesn't we create a new xattr. If @flags is zero we simply
* insert the new xattr replacing any existing one.
*
* If @value is empty and a matching xattr object is found we delete it if
* XATTR_REPLACE is specified in @flags or @flags is zero.
*
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
* If @value is empty and no matching xattr object for @name is found we do
* nothing if XATTR_CREATE is specified in @flags or @flags is zero. For
* XATTR_REPLACE we fail as mentioned above.
*
* Return: On success, the removed or replaced xattr is returned, to be freed
* by the caller; or NULL if none. On failure a negative error code is returned.
*/
struct simple_xattr *simple_xattr_set(struct simple_xattrs *xattrs,
const char *name, const void *value,
size_t size, int flags)
{
struct simple_xattr *old_xattr = NULL, *new_xattr = NULL;
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
struct rb_node *parent = NULL, **rbp;
int err = 0, ret;
/* value == NULL means remove */
if (value) {
new_xattr = simple_xattr_alloc(value, size);
if (!new_xattr)
return ERR_PTR(-ENOMEM);
new_xattr->name = kstrdup(name, GFP_KERNEL_ACCOUNT);
if (!new_xattr->name) {
simple_xattr_free(new_xattr);
return ERR_PTR(-ENOMEM);
}
}
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
write_lock(&xattrs->lock);
rbp = &xattrs->rb_root.rb_node;
while (*rbp) {
parent = *rbp;
ret = rbtree_simple_xattr_cmp(name, *rbp);
if (ret < 0)
rbp = &(*rbp)->rb_left;
else if (ret > 0)
rbp = &(*rbp)->rb_right;
else
old_xattr = rb_entry(*rbp, struct simple_xattr, rb_node);
if (old_xattr)
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
break;
}
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
if (old_xattr) {
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
/* Fail if XATTR_CREATE is requested and the xattr exists. */
if (flags & XATTR_CREATE) {
err = -EEXIST;
goto out_unlock;
}
if (new_xattr)
rb_replace_node(&old_xattr->rb_node,
&new_xattr->rb_node, &xattrs->rb_root);
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
else
rb_erase(&old_xattr->rb_node, &xattrs->rb_root);
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
} else {
/* Fail if XATTR_REPLACE is requested but no xattr is found. */
if (flags & XATTR_REPLACE) {
err = -ENODATA;
goto out_unlock;
}
/*
* If XATTR_CREATE or no flags are specified together with a
* new value simply insert it.
*/
if (new_xattr) {
rb_link_node(&new_xattr->rb_node, parent, rbp);
rb_insert_color(&new_xattr->rb_node, &xattrs->rb_root);
}
/*
* If XATTR_CREATE or no flags are specified and neither an
* old or new xattr exist then we don't need to do anything.
*/
}
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
out_unlock:
write_unlock(&xattrs->lock);
if (!err)
return old_xattr;
simple_xattr_free(new_xattr);
return ERR_PTR(err);
}
static bool xattr_is_trusted(const char *name)
{
return !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN);
}
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
/**
* simple_xattr_list - list all xattr objects
* @inode: inode from which to get the xattrs
* @xattrs: the header of the xattr object
* @buffer: the buffer to store all xattrs into
* @size: the size of @buffer
*
* List all xattrs associated with @inode. If @buffer is NULL we returned
* the required size of the buffer. If @buffer is provided we store the
* xattrs value into it provided it is big enough.
*
* Note, the number of xattr names that can be listed with listxattr(2) is
* limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed
* then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names
* are found it will return -E2BIG.
*
* Return: On success the required size or the size of the copied xattrs is
* returned. On error a negative error code is returned.
*/
ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs,
char *buffer, size_t size)
{
bool trusted = ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN);
struct simple_xattr *xattr;
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
struct rb_node *rbp;
ssize_t remaining_size = size;
int err = 0;
err = posix_acl_listxattr(inode, &buffer, &remaining_size);
if (err)
return err;
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
read_lock(&xattrs->lock);
for (rbp = rb_first(&xattrs->rb_root); rbp; rbp = rb_next(rbp)) {
xattr = rb_entry(rbp, struct simple_xattr, rb_node);
/* skip "trusted." attributes for unprivileged callers */
if (!trusted && xattr_is_trusted(xattr->name))
continue;
err = xattr_list_one(&buffer, &remaining_size, xattr->name);
if (err)
break;
}
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
read_unlock(&xattrs->lock);
return err ? err : size - remaining_size;
}
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
/**
* rbtree_simple_xattr_less - compare two xattr rbtree nodes
* @new_node: new node
* @node: current node
*
* Compare the xattr attached to @new_node with the xattr attached to @node.
* Note that this function technically tolerates duplicate entries.
*
* Return: True if insertion point in the rbtree is found.
*/
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
static bool rbtree_simple_xattr_less(struct rb_node *new_node,
const struct rb_node *node)
{
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
return rbtree_simple_xattr_node_cmp(new_node, node) < 0;
}
/**
* simple_xattr_add - add xattr objects
* @xattrs: the header of the xattr object
* @new_xattr: the xattr object to add
*
* Add an xattr object to @xattrs. This assumes no replacement or removal
* of matching xattrs is wanted. Should only be called during inode
* initialization when a few distinct initial xattrs are supposed to be set.
*/
void simple_xattr_add(struct simple_xattrs *xattrs,
struct simple_xattr *new_xattr)
{
write_lock(&xattrs->lock);
rb_add(&new_xattr->rb_node, &xattrs->rb_root, rbtree_simple_xattr_less);
write_unlock(&xattrs->lock);
}
/**
* simple_xattrs_init - initialize new xattr header
* @xattrs: header to initialize
*
* Initialize relevant fields of a an xattr header.
*/
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
void simple_xattrs_init(struct simple_xattrs *xattrs)
{
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
xattrs->rb_root = RB_ROOT;
rwlock_init(&xattrs->lock);
}
/**
* simple_xattrs_free - free xattrs
* @xattrs: xattr header whose xattrs to destroy
tmpfs,xattr: enable limited user extended attributes Enable "user." extended attributes on tmpfs, limiting them by tracking the space they occupy, and deducting that space from the limited ispace (unless tmpfs mounted with nr_inodes=0 to leave that ispace unlimited). tmpfs inodes and simple xattrs are both unswappable, and have to be in lowmem on a 32-bit highmem kernel: so the ispace limit is appropriate for xattrs, without any need for a further mount option. Add simple_xattr_space() to give approximate but deterministic estimate of the space taken up by each xattr: with simple_xattrs_free() outputting the space freed if required (but kernfs and even some tmpfs usages do not require that, so don't waste time on strlen'ing if not needed). Security and trusted xattrs were already supported: for consistency and simplicity, account them from the same pool; though there's a small risk that a tmpfs with enough space before would now be considered too small. When extended attributes are used, "df -i" does show more IUsed and less IFree than can be explained by the inodes: document that (manpage later). xfstests tests/generic which were not run on tmpfs before but now pass: 020 037 062 070 077 097 103 117 337 377 454 486 523 533 611 618 728 with no new failures. Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com> Message-Id: <2e63b26e-df46-5baa-c7d6-f9a8dd3282c5@google.com> Signed-off-by: Christian Brauner <brauner@kernel.org>
2023-08-09 04:33:56 +00:00
* @freed_space: approximate number of bytes of memory freed from @xattrs
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
*
* Destroy all xattrs in @xattr. When this is called no one can hold a
* reference to any of the xattrs anymore.
*/
tmpfs,xattr: enable limited user extended attributes Enable "user." extended attributes on tmpfs, limiting them by tracking the space they occupy, and deducting that space from the limited ispace (unless tmpfs mounted with nr_inodes=0 to leave that ispace unlimited). tmpfs inodes and simple xattrs are both unswappable, and have to be in lowmem on a 32-bit highmem kernel: so the ispace limit is appropriate for xattrs, without any need for a further mount option. Add simple_xattr_space() to give approximate but deterministic estimate of the space taken up by each xattr: with simple_xattrs_free() outputting the space freed if required (but kernfs and even some tmpfs usages do not require that, so don't waste time on strlen'ing if not needed). Security and trusted xattrs were already supported: for consistency and simplicity, account them from the same pool; though there's a small risk that a tmpfs with enough space before would now be considered too small. When extended attributes are used, "df -i" does show more IUsed and less IFree than can be explained by the inodes: document that (manpage later). xfstests tests/generic which were not run on tmpfs before but now pass: 020 037 062 070 077 097 103 117 337 377 454 486 523 533 611 618 728 with no new failures. Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com> Message-Id: <2e63b26e-df46-5baa-c7d6-f9a8dd3282c5@google.com> Signed-off-by: Christian Brauner <brauner@kernel.org>
2023-08-09 04:33:56 +00:00
void simple_xattrs_free(struct simple_xattrs *xattrs, size_t *freed_space)
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
{
struct rb_node *rbp;
tmpfs,xattr: enable limited user extended attributes Enable "user." extended attributes on tmpfs, limiting them by tracking the space they occupy, and deducting that space from the limited ispace (unless tmpfs mounted with nr_inodes=0 to leave that ispace unlimited). tmpfs inodes and simple xattrs are both unswappable, and have to be in lowmem on a 32-bit highmem kernel: so the ispace limit is appropriate for xattrs, without any need for a further mount option. Add simple_xattr_space() to give approximate but deterministic estimate of the space taken up by each xattr: with simple_xattrs_free() outputting the space freed if required (but kernfs and even some tmpfs usages do not require that, so don't waste time on strlen'ing if not needed). Security and trusted xattrs were already supported: for consistency and simplicity, account them from the same pool; though there's a small risk that a tmpfs with enough space before would now be considered too small. When extended attributes are used, "df -i" does show more IUsed and less IFree than can be explained by the inodes: document that (manpage later). xfstests tests/generic which were not run on tmpfs before but now pass: 020 037 062 070 077 097 103 117 337 377 454 486 523 533 611 618 728 with no new failures. Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com> Message-Id: <2e63b26e-df46-5baa-c7d6-f9a8dd3282c5@google.com> Signed-off-by: Christian Brauner <brauner@kernel.org>
2023-08-09 04:33:56 +00:00
if (freed_space)
*freed_space = 0;
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
rbp = rb_first(&xattrs->rb_root);
while (rbp) {
struct simple_xattr *xattr;
struct rb_node *rbp_next;
rbp_next = rb_next(rbp);
xattr = rb_entry(rbp, struct simple_xattr, rb_node);
rb_erase(&xattr->rb_node, &xattrs->rb_root);
tmpfs,xattr: enable limited user extended attributes Enable "user." extended attributes on tmpfs, limiting them by tracking the space they occupy, and deducting that space from the limited ispace (unless tmpfs mounted with nr_inodes=0 to leave that ispace unlimited). tmpfs inodes and simple xattrs are both unswappable, and have to be in lowmem on a 32-bit highmem kernel: so the ispace limit is appropriate for xattrs, without any need for a further mount option. Add simple_xattr_space() to give approximate but deterministic estimate of the space taken up by each xattr: with simple_xattrs_free() outputting the space freed if required (but kernfs and even some tmpfs usages do not require that, so don't waste time on strlen'ing if not needed). Security and trusted xattrs were already supported: for consistency and simplicity, account them from the same pool; though there's a small risk that a tmpfs with enough space before would now be considered too small. When extended attributes are used, "df -i" does show more IUsed and less IFree than can be explained by the inodes: document that (manpage later). xfstests tests/generic which were not run on tmpfs before but now pass: 020 037 062 070 077 097 103 117 337 377 454 486 523 533 611 618 728 with no new failures. Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com> Message-Id: <2e63b26e-df46-5baa-c7d6-f9a8dd3282c5@google.com> Signed-off-by: Christian Brauner <brauner@kernel.org>
2023-08-09 04:33:56 +00:00
if (freed_space)
*freed_space += simple_xattr_space(xattr->name,
xattr->size);
simple_xattr_free(xattr);
xattr: use rbtree for simple_xattrs A while ago Vasily reported that it is possible to set a large number of xattrs on inodes of filesystems that make use of the simple xattr infrastructure. This includes all kernfs-based filesystems that support xattrs (e.g., cgroupfs and tmpfs). Both cgroupfs and tmpfs can be mounted by unprivileged users in unprivileged containers and root in an unprivileged container can set an unrestricted number of security.* xattrs and privileged users can also set unlimited trusted.* xattrs. As there are apparently users that have a fairly large number of xattrs we should scale a bit better. Other xattrs such as user.* are restricted for kernfs-based instances to a fairly limited number. Using a simple linked list protected by a spinlock used for set, get, and list operations doesn't scale well if users use a lot of xattrs even if it's not a crazy number. There's no need to bring in the big guns like rhashtables or rw semaphores for this. An rbtree with a rwlock, or limited rcu semanics and seqlock is enough. It scales within the constraints we are working in. By far the most common operation is getting an xattr. Setting xattrs should be a moderately rare operation. And listxattr() often only happens when copying xattrs between files or together with the contents to a new file. Holding a lock across listxattr() is unproblematic because it doesn't list the values of xattrs. It can only be used to list the names of all xattrs set on a file. And the number of xattr names that can be listed with listxattr() is limited to XATTR_LIST_MAX aka 65536 bytes. If a larger buffer is passed then vfs_listxattr() caps it to XATTR_LIST_MAX and if more xattr names are found it will return -E2BIG. In short, the maximum amount of memory that can be retrieved via listxattr() is limited. Of course, the API is broken as documented on xattr(7) already. In the future we might want to address this but for now this is the world we live in and have lived for a long time. But it does indeed mean that once an application goes over XATTR_LIST_MAX limit of xattrs set on an inode it isn't possible to copy the file and include its xattrs in the copy unless the caller knows all xattrs or limits the copy of the xattrs to important ones it knows by name (At least for tmpfs, and kernfs-based filesystems. Other filesystems might provide ways of achieving this.). Bonus of this port to rbtree+rwlock is that we shrink the memory consumption for users of the simple xattr infrastructure. Also add proper kernel documentation to all the functions. A big thanks to Paul for his comments. Cc: Vasily Averin <vvs@openvz.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-11-04 12:52:42 +00:00
rbp = rbp_next;
}
}