linux/fs/xattr.c
Andi Kleen 69b4573296 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 12:02:09 -04:00

699 lines
16 KiB
C

/*
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/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/module.h>
#include <linux/fsnotify.h>
#include <linux/audit.h>
#include <asm/uaccess.h>
/*
* Check permissions for extended attribute access. This is a bit complicated
* because different namespaces have very different rules.
*/
static int
xattr_permission(struct inode *inode, const char *name, int mask)
{
/*
* We can never set or remove an extended attribute on a read-only
* filesystem or on an immutable / append-only inode.
*/
if (mask & MAY_WRITE) {
if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
return -EPERM;
}
/*
* 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(inode))
return -EPERM;
}
return inode_permission(inode, mask);
}
/**
* __vfs_setxattr_noperm - perform setxattr operation without performing
* permission checks.
*
* @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 dentry *dentry, const char *name,
const void *value, size_t size, int flags)
{
struct inode *inode = dentry->d_inode;
int error = -EOPNOTSUPP;
int issec = !strncmp(name, XATTR_SECURITY_PREFIX,
XATTR_SECURITY_PREFIX_LEN);
if (issec)
inode->i_flags &= ~S_NOSEC;
if (inode->i_op->setxattr) {
error = inode->i_op->setxattr(dentry, name, value, size, flags);
if (!error) {
fsnotify_xattr(dentry);
security_inode_post_setxattr(dentry, name, value,
size, flags);
}
} else 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;
}
int
vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
size_t size, int flags)
{
struct inode *inode = dentry->d_inode;
int error;
error = xattr_permission(inode, name, MAY_WRITE);
if (error)
return error;
mutex_lock(&inode->i_mutex);
error = security_inode_setxattr(dentry, name, value, size, flags);
if (error)
goto out;
error = __vfs_setxattr_noperm(dentry, name, value, size, flags);
out:
mutex_unlock(&inode->i_mutex);
return error;
}
EXPORT_SYMBOL_GPL(vfs_setxattr);
ssize_t
xattr_getsecurity(struct inode *inode, const char *name, void *value,
size_t size)
{
void *buffer = NULL;
ssize_t len;
if (!value || !size) {
len = security_inode_getsecurity(inode, name, &buffer, false);
goto out_noalloc;
}
len = security_inode_getsecurity(inode, name, &buffer, true);
if (len < 0)
return len;
if (size < len) {
len = -ERANGE;
goto out;
}
memcpy(value, buffer, len);
out:
security_release_secctx(buffer, len);
out_noalloc:
return len;
}
EXPORT_SYMBOL_GPL(xattr_getsecurity);
ssize_t
vfs_getxattr(struct dentry *dentry, const char *name, void *value, size_t size)
{
struct inode *inode = dentry->d_inode;
int error;
error = xattr_permission(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(inode, suffix, value, size);
/*
* Only overwrite the return value if a security module
* is actually active.
*/
if (ret == -EOPNOTSUPP)
goto nolsm;
return ret;
}
nolsm:
if (inode->i_op->getxattr)
error = inode->i_op->getxattr(dentry, name, value, size);
else
error = -EOPNOTSUPP;
return error;
}
EXPORT_SYMBOL_GPL(vfs_getxattr);
ssize_t
vfs_listxattr(struct dentry *d, char *list, size_t size)
{
ssize_t error;
error = security_inode_listxattr(d);
if (error)
return error;
error = -EOPNOTSUPP;
if (d->d_inode->i_op->listxattr) {
error = d->d_inode->i_op->listxattr(d, list, size);
} else {
error = security_inode_listsecurity(d->d_inode, list, size);
if (size && error > size)
error = -ERANGE;
}
return error;
}
EXPORT_SYMBOL_GPL(vfs_listxattr);
int
vfs_removexattr(struct dentry *dentry, const char *name)
{
struct inode *inode = dentry->d_inode;
int error;
if (!inode->i_op->removexattr)
return -EOPNOTSUPP;
error = xattr_permission(inode, name, MAY_WRITE);
if (error)
return error;
error = security_inode_removexattr(dentry, name);
if (error)
return error;
mutex_lock(&inode->i_mutex);
error = inode->i_op->removexattr(dentry, name);
mutex_unlock(&inode->i_mutex);
if (!error)
fsnotify_xattr(dentry);
return error;
}
EXPORT_SYMBOL_GPL(vfs_removexattr);
/*
* Extended attribute SET operations
*/
static long
setxattr(struct dentry *d, const char __user *name, const void __user *value,
size_t size, int flags)
{
int error;
void *kvalue = NULL;
char kname[XATTR_NAME_MAX + 1];
if (flags & ~(XATTR_CREATE|XATTR_REPLACE))
return -EINVAL;
error = strncpy_from_user(kname, name, sizeof(kname));
if (error == 0 || error == sizeof(kname))
error = -ERANGE;
if (error < 0)
return error;
if (size) {
if (size > XATTR_SIZE_MAX)
return -E2BIG;
kvalue = memdup_user(value, size);
if (IS_ERR(kvalue))
return PTR_ERR(kvalue);
}
error = vfs_setxattr(d, kname, kvalue, size, flags);
kfree(kvalue);
return error;
}
SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
const char __user *, name, const void __user *, value,
size_t, size, int, flags)
{
struct path path;
int error;
error = user_path(pathname, &path);
if (error)
return error;
error = mnt_want_write(path.mnt);
if (!error) {
error = setxattr(path.dentry, name, value, size, flags);
mnt_drop_write(path.mnt);
}
path_put(&path);
return error;
}
SYSCALL_DEFINE5(lsetxattr, const char __user *, pathname,
const char __user *, name, const void __user *, value,
size_t, size, int, flags)
{
struct path path;
int error;
error = user_lpath(pathname, &path);
if (error)
return error;
error = mnt_want_write(path.mnt);
if (!error) {
error = setxattr(path.dentry, name, value, size, flags);
mnt_drop_write(path.mnt);
}
path_put(&path);
return error;
}
SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
const void __user *,value, size_t, size, int, flags)
{
struct file *f;
struct dentry *dentry;
int error = -EBADF;
f = fget(fd);
if (!f)
return error;
dentry = f->f_path.dentry;
audit_inode(NULL, dentry);
error = mnt_want_write_file(f);
if (!error) {
error = setxattr(dentry, name, value, size, flags);
mnt_drop_write(f->f_path.mnt);
}
fput(f);
return error;
}
/*
* Extended attribute GET operations
*/
static ssize_t
getxattr(struct dentry *d, const char __user *name, void __user *value,
size_t size)
{
ssize_t error;
void *kvalue = NULL;
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 (size) {
if (size > XATTR_SIZE_MAX)
size = XATTR_SIZE_MAX;
kvalue = kzalloc(size, GFP_KERNEL);
if (!kvalue)
return -ENOMEM;
}
error = vfs_getxattr(d, kname, kvalue, size);
if (error > 0) {
if (size && copy_to_user(value, kvalue, error))
error = -EFAULT;
} else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
/* The file system tried to returned a value bigger
than XATTR_SIZE_MAX bytes. Not possible. */
error = -E2BIG;
}
kfree(kvalue);
return error;
}
SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
const char __user *, name, void __user *, value, size_t, size)
{
struct path path;
ssize_t error;
error = user_path(pathname, &path);
if (error)
return error;
error = getxattr(path.dentry, name, value, size);
path_put(&path);
return error;
}
SYSCALL_DEFINE4(lgetxattr, const char __user *, pathname,
const char __user *, name, void __user *, value, size_t, size)
{
struct path path;
ssize_t error;
error = user_lpath(pathname, &path);
if (error)
return error;
error = getxattr(path.dentry, name, value, size);
path_put(&path);
return error;
}
SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
void __user *, value, size_t, size)
{
struct file *f;
ssize_t error = -EBADF;
f = fget(fd);
if (!f)
return error;
audit_inode(NULL, f->f_path.dentry);
error = getxattr(f->f_path.dentry, name, value, size);
fput(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;
klist = kmalloc(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;
}
kfree(klist);
return error;
}
SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
size_t, size)
{
struct path path;
ssize_t error;
error = user_path(pathname, &path);
if (error)
return error;
error = listxattr(path.dentry, list, size);
path_put(&path);
return error;
}
SYSCALL_DEFINE3(llistxattr, const char __user *, pathname, char __user *, list,
size_t, size)
{
struct path path;
ssize_t error;
error = user_lpath(pathname, &path);
if (error)
return error;
error = listxattr(path.dentry, list, size);
path_put(&path);
return error;
}
SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)
{
struct file *f;
ssize_t error = -EBADF;
f = fget(fd);
if (!f)
return error;
audit_inode(NULL, f->f_path.dentry);
error = listxattr(f->f_path.dentry, list, size);
fput(f);
return error;
}
/*
* Extended attribute REMOVE operations
*/
static long
removexattr(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;
return vfs_removexattr(d, kname);
}
SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
const char __user *, name)
{
struct path path;
int error;
error = user_path(pathname, &path);
if (error)
return error;
error = mnt_want_write(path.mnt);
if (!error) {
error = removexattr(path.dentry, name);
mnt_drop_write(path.mnt);
}
path_put(&path);
return error;
}
SYSCALL_DEFINE2(lremovexattr, const char __user *, pathname,
const char __user *, name)
{
struct path path;
int error;
error = user_lpath(pathname, &path);
if (error)
return error;
error = mnt_want_write(path.mnt);
if (!error) {
error = removexattr(path.dentry, name);
mnt_drop_write(path.mnt);
}
path_put(&path);
return error;
}
SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)
{
struct file *f;
struct dentry *dentry;
int error = -EBADF;
f = fget(fd);
if (!f)
return error;
dentry = f->f_path.dentry;
audit_inode(NULL, dentry);
error = mnt_want_write_file(f);
if (!error) {
error = removexattr(dentry, name);
mnt_drop_write(f->f_path.mnt);
}
fput(f);
return error;
}
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 with the generic xattr API, 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.
*
* The generic_fooxattr() functions will use this list to dispatch xattr
* operations to the correct xattr_handler.
*/
#define for_each_xattr_handler(handlers, handler) \
for ((handler) = *(handlers)++; \
(handler) != NULL; \
(handler) = *(handlers)++)
/*
* Find the xattr_handler with the matching prefix.
*/
static const struct xattr_handler *
xattr_resolve_name(const struct xattr_handler **handlers, const char **name)
{
const struct xattr_handler *handler;
if (!*name)
return NULL;
for_each_xattr_handler(handlers, handler) {
const char *n = strcmp_prefix(*name, handler->prefix);
if (n) {
*name = n;
break;
}
}
return handler;
}
/*
* Find the handler for the prefix and dispatch its get() operation.
*/
ssize_t
generic_getxattr(struct dentry *dentry, const char *name, void *buffer, size_t size)
{
const struct xattr_handler *handler;
handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
if (!handler)
return -EOPNOTSUPP;
return handler->get(dentry, name, buffer, size, handler->flags);
}
/*
* Combine the results of the list() operation from every xattr_handler in the
* list.
*/
ssize_t
generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
{
const struct xattr_handler *handler, **handlers = dentry->d_sb->s_xattr;
unsigned int size = 0;
if (!buffer) {
for_each_xattr_handler(handlers, handler) {
size += handler->list(dentry, NULL, 0, NULL, 0,
handler->flags);
}
} else {
char *buf = buffer;
for_each_xattr_handler(handlers, handler) {
size = handler->list(dentry, buf, buffer_size,
NULL, 0, handler->flags);
if (size > buffer_size)
return -ERANGE;
buf += size;
buffer_size -= size;
}
size = buf - buffer;
}
return size;
}
/*
* Find the handler for the prefix and dispatch its set() operation.
*/
int
generic_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags)
{
const struct xattr_handler *handler;
if (size == 0)
value = ""; /* empty EA, do not remove */
handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
if (!handler)
return -EOPNOTSUPP;
return handler->set(dentry, name, value, size, flags, handler->flags);
}
/*
* Find the handler for the prefix and dispatch its set() operation to remove
* any associated extended attribute.
*/
int
generic_removexattr(struct dentry *dentry, const char *name)
{
const struct xattr_handler *handler;
handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
if (!handler)
return -EOPNOTSUPP;
return handler->set(dentry, name, NULL, 0,
XATTR_REPLACE, handler->flags);
}
EXPORT_SYMBOL(generic_getxattr);
EXPORT_SYMBOL(generic_listxattr);
EXPORT_SYMBOL(generic_setxattr);
EXPORT_SYMBOL(generic_removexattr);