linux/security/commoncap.c
Linus Torvalds dd198ce714 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace
Pull namespace updates from Eric Biederman:
 "Life has been busy and I have not gotten half as much done this round
  as I would have liked. I delayed it so that a minor conflict
  resolution with the mips tree could spend a little time in linux-next
  before I sent this pull request.

  This includes two long delayed user namespace changes from Kirill
  Tkhai. It also includes a very useful change from Serge Hallyn that
  allows the security capability attribute to be used inside of user
  namespaces. The practical effect of this is people can now untar
  tarballs and install rpms in user namespaces. It had been suggested to
  generalize this and encode some of the namespace information
  information in the xattr name. Upon close inspection that makes the
  things that should be hard easy and the things that should be easy
  more expensive.

  Then there is my bugfix/cleanup for signal injection that removes the
  magic encoding of the siginfo union member from the kernel internal
  si_code. The mips folks reported the case where I had used FPE_FIXME
  me is impossible so I have remove FPE_FIXME from mips, while at the
  same time including a return statement in that case to keep gcc from
  complaining about unitialized variables.

  I almost finished the work to get make copy_siginfo_to_user a trivial
  copy to user. The code is available at:

     git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git neuter-copy_siginfo_to_user-v3

  But I did not have time/energy to get the code posted and reviewed
  before the merge window opened.

  I was able to see that the security excuse for just copying fields
  that we know are initialized doesn't work in practice there are buggy
  initializations that don't initialize the proper fields in siginfo. So
  we still sometimes copy unitialized data to userspace"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  Introduce v3 namespaced file capabilities
  mips/signal: In force_fcr31_sig return in the impossible case
  signal: Remove kernel interal si_code magic
  fcntl: Don't use ambiguous SIG_POLL si_codes
  prctl: Allow local CAP_SYS_ADMIN changing exe_file
  security: Use user_namespace::level to avoid redundant iterations in cap_capable()
  userns,pidns: Verify the userns for new pid namespaces
  signal/testing: Don't look for __SI_FAULT in userspace
  signal/mips: Document a conflict with SI_USER with SIGFPE
  signal/sparc: Document a conflict with SI_USER with SIGFPE
  signal/ia64: Document a conflict with SI_USER with SIGFPE
  signal/alpha: Document a conflict with SI_USER for SIGTRAP
2017-09-11 18:34:47 -07:00

1309 lines
37 KiB
C

/* Common capabilities, needed by capability.o.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
*/
#include <linux/capability.h>
#include <linux/audit.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/lsm_hooks.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/skbuff.h>
#include <linux/netlink.h>
#include <linux/ptrace.h>
#include <linux/xattr.h>
#include <linux/hugetlb.h>
#include <linux/mount.h>
#include <linux/sched.h>
#include <linux/prctl.h>
#include <linux/securebits.h>
#include <linux/user_namespace.h>
#include <linux/binfmts.h>
#include <linux/personality.h>
/*
* If a non-root user executes a setuid-root binary in
* !secure(SECURE_NOROOT) mode, then we raise capabilities.
* However if fE is also set, then the intent is for only
* the file capabilities to be applied, and the setuid-root
* bit is left on either to change the uid (plausible) or
* to get full privilege on a kernel without file capabilities
* support. So in that case we do not raise capabilities.
*
* Warn if that happens, once per boot.
*/
static void warn_setuid_and_fcaps_mixed(const char *fname)
{
static int warned;
if (!warned) {
printk(KERN_INFO "warning: `%s' has both setuid-root and"
" effective capabilities. Therefore not raising all"
" capabilities.\n", fname);
warned = 1;
}
}
/**
* cap_capable - Determine whether a task has a particular effective capability
* @cred: The credentials to use
* @ns: The user namespace in which we need the capability
* @cap: The capability to check for
* @audit: Whether to write an audit message or not
*
* Determine whether the nominated task has the specified capability amongst
* its effective set, returning 0 if it does, -ve if it does not.
*
* NOTE WELL: cap_has_capability() cannot be used like the kernel's capable()
* and has_capability() functions. That is, it has the reverse semantics:
* cap_has_capability() returns 0 when a task has a capability, but the
* kernel's capable() and has_capability() returns 1 for this case.
*/
int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
int cap, int audit)
{
struct user_namespace *ns = targ_ns;
/* See if cred has the capability in the target user namespace
* by examining the target user namespace and all of the target
* user namespace's parents.
*/
for (;;) {
/* Do we have the necessary capabilities? */
if (ns == cred->user_ns)
return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;
/*
* If we're already at a lower level than we're looking for,
* we're done searching.
*/
if (ns->level <= cred->user_ns->level)
return -EPERM;
/*
* The owner of the user namespace in the parent of the
* user namespace has all caps.
*/
if ((ns->parent == cred->user_ns) && uid_eq(ns->owner, cred->euid))
return 0;
/*
* If you have a capability in a parent user ns, then you have
* it over all children user namespaces as well.
*/
ns = ns->parent;
}
/* We never get here */
}
/**
* cap_settime - Determine whether the current process may set the system clock
* @ts: The time to set
* @tz: The timezone to set
*
* Determine whether the current process may set the system clock and timezone
* information, returning 0 if permission granted, -ve if denied.
*/
int cap_settime(const struct timespec64 *ts, const struct timezone *tz)
{
if (!capable(CAP_SYS_TIME))
return -EPERM;
return 0;
}
/**
* cap_ptrace_access_check - Determine whether the current process may access
* another
* @child: The process to be accessed
* @mode: The mode of attachment.
*
* If we are in the same or an ancestor user_ns and have all the target
* task's capabilities, then ptrace access is allowed.
* If we have the ptrace capability to the target user_ns, then ptrace
* access is allowed.
* Else denied.
*
* Determine whether a process may access another, returning 0 if permission
* granted, -ve if denied.
*/
int cap_ptrace_access_check(struct task_struct *child, unsigned int mode)
{
int ret = 0;
const struct cred *cred, *child_cred;
const kernel_cap_t *caller_caps;
rcu_read_lock();
cred = current_cred();
child_cred = __task_cred(child);
if (mode & PTRACE_MODE_FSCREDS)
caller_caps = &cred->cap_effective;
else
caller_caps = &cred->cap_permitted;
if (cred->user_ns == child_cred->user_ns &&
cap_issubset(child_cred->cap_permitted, *caller_caps))
goto out;
if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE))
goto out;
ret = -EPERM;
out:
rcu_read_unlock();
return ret;
}
/**
* cap_ptrace_traceme - Determine whether another process may trace the current
* @parent: The task proposed to be the tracer
*
* If parent is in the same or an ancestor user_ns and has all current's
* capabilities, then ptrace access is allowed.
* If parent has the ptrace capability to current's user_ns, then ptrace
* access is allowed.
* Else denied.
*
* Determine whether the nominated task is permitted to trace the current
* process, returning 0 if permission is granted, -ve if denied.
*/
int cap_ptrace_traceme(struct task_struct *parent)
{
int ret = 0;
const struct cred *cred, *child_cred;
rcu_read_lock();
cred = __task_cred(parent);
child_cred = current_cred();
if (cred->user_ns == child_cred->user_ns &&
cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
goto out;
if (has_ns_capability(parent, child_cred->user_ns, CAP_SYS_PTRACE))
goto out;
ret = -EPERM;
out:
rcu_read_unlock();
return ret;
}
/**
* cap_capget - Retrieve a task's capability sets
* @target: The task from which to retrieve the capability sets
* @effective: The place to record the effective set
* @inheritable: The place to record the inheritable set
* @permitted: The place to record the permitted set
*
* This function retrieves the capabilities of the nominated task and returns
* them to the caller.
*/
int cap_capget(struct task_struct *target, kernel_cap_t *effective,
kernel_cap_t *inheritable, kernel_cap_t *permitted)
{
const struct cred *cred;
/* Derived from kernel/capability.c:sys_capget. */
rcu_read_lock();
cred = __task_cred(target);
*effective = cred->cap_effective;
*inheritable = cred->cap_inheritable;
*permitted = cred->cap_permitted;
rcu_read_unlock();
return 0;
}
/*
* Determine whether the inheritable capabilities are limited to the old
* permitted set. Returns 1 if they are limited, 0 if they are not.
*/
static inline int cap_inh_is_capped(void)
{
/* they are so limited unless the current task has the CAP_SETPCAP
* capability
*/
if (cap_capable(current_cred(), current_cred()->user_ns,
CAP_SETPCAP, SECURITY_CAP_AUDIT) == 0)
return 0;
return 1;
}
/**
* cap_capset - Validate and apply proposed changes to current's capabilities
* @new: The proposed new credentials; alterations should be made here
* @old: The current task's current credentials
* @effective: A pointer to the proposed new effective capabilities set
* @inheritable: A pointer to the proposed new inheritable capabilities set
* @permitted: A pointer to the proposed new permitted capabilities set
*
* This function validates and applies a proposed mass change to the current
* process's capability sets. The changes are made to the proposed new
* credentials, and assuming no error, will be committed by the caller of LSM.
*/
int cap_capset(struct cred *new,
const struct cred *old,
const kernel_cap_t *effective,
const kernel_cap_t *inheritable,
const kernel_cap_t *permitted)
{
if (cap_inh_is_capped() &&
!cap_issubset(*inheritable,
cap_combine(old->cap_inheritable,
old->cap_permitted)))
/* incapable of using this inheritable set */
return -EPERM;
if (!cap_issubset(*inheritable,
cap_combine(old->cap_inheritable,
old->cap_bset)))
/* no new pI capabilities outside bounding set */
return -EPERM;
/* verify restrictions on target's new Permitted set */
if (!cap_issubset(*permitted, old->cap_permitted))
return -EPERM;
/* verify the _new_Effective_ is a subset of the _new_Permitted_ */
if (!cap_issubset(*effective, *permitted))
return -EPERM;
new->cap_effective = *effective;
new->cap_inheritable = *inheritable;
new->cap_permitted = *permitted;
/*
* Mask off ambient bits that are no longer both permitted and
* inheritable.
*/
new->cap_ambient = cap_intersect(new->cap_ambient,
cap_intersect(*permitted,
*inheritable));
if (WARN_ON(!cap_ambient_invariant_ok(new)))
return -EINVAL;
return 0;
}
/**
* cap_inode_need_killpriv - Determine if inode change affects privileges
* @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV
*
* Determine if an inode having a change applied that's marked ATTR_KILL_PRIV
* affects the security markings on that inode, and if it is, should
* inode_killpriv() be invoked or the change rejected?
*
* Returns 0 if granted; +ve if granted, but inode_killpriv() is required; and
* -ve to deny the change.
*/
int cap_inode_need_killpriv(struct dentry *dentry)
{
struct inode *inode = d_backing_inode(dentry);
int error;
error = __vfs_getxattr(dentry, inode, XATTR_NAME_CAPS, NULL, 0);
return error > 0;
}
/**
* cap_inode_killpriv - Erase the security markings on an inode
* @dentry: The inode/dentry to alter
*
* Erase the privilege-enhancing security markings on an inode.
*
* Returns 0 if successful, -ve on error.
*/
int cap_inode_killpriv(struct dentry *dentry)
{
int error;
error = __vfs_removexattr(dentry, XATTR_NAME_CAPS);
if (error == -EOPNOTSUPP)
error = 0;
return error;
}
static bool rootid_owns_currentns(kuid_t kroot)
{
struct user_namespace *ns;
if (!uid_valid(kroot))
return false;
for (ns = current_user_ns(); ; ns = ns->parent) {
if (from_kuid(ns, kroot) == 0)
return true;
if (ns == &init_user_ns)
break;
}
return false;
}
static __u32 sansflags(__u32 m)
{
return m & ~VFS_CAP_FLAGS_EFFECTIVE;
}
static bool is_v2header(size_t size, __le32 magic)
{
__u32 m = le32_to_cpu(magic);
if (size != XATTR_CAPS_SZ_2)
return false;
return sansflags(m) == VFS_CAP_REVISION_2;
}
static bool is_v3header(size_t size, __le32 magic)
{
__u32 m = le32_to_cpu(magic);
if (size != XATTR_CAPS_SZ_3)
return false;
return sansflags(m) == VFS_CAP_REVISION_3;
}
/*
* getsecurity: We are called for security.* before any attempt to read the
* xattr from the inode itself.
*
* This gives us a chance to read the on-disk value and convert it. If we
* return -EOPNOTSUPP, then vfs_getxattr() will call the i_op handler.
*
* Note we are not called by vfs_getxattr_alloc(), but that is only called
* by the integrity subsystem, which really wants the unconverted values -
* so that's good.
*/
int cap_inode_getsecurity(struct inode *inode, const char *name, void **buffer,
bool alloc)
{
int size, ret;
kuid_t kroot;
uid_t root, mappedroot;
char *tmpbuf = NULL;
struct vfs_cap_data *cap;
struct vfs_ns_cap_data *nscap;
struct dentry *dentry;
struct user_namespace *fs_ns;
if (strcmp(name, "capability") != 0)
return -EOPNOTSUPP;
dentry = d_find_alias(inode);
if (!dentry)
return -EINVAL;
size = sizeof(struct vfs_ns_cap_data);
ret = (int) vfs_getxattr_alloc(dentry, XATTR_NAME_CAPS,
&tmpbuf, size, GFP_NOFS);
dput(dentry);
if (ret < 0)
return ret;
fs_ns = inode->i_sb->s_user_ns;
cap = (struct vfs_cap_data *) tmpbuf;
if (is_v2header((size_t) ret, cap->magic_etc)) {
/* If this is sizeof(vfs_cap_data) then we're ok with the
* on-disk value, so return that. */
if (alloc)
*buffer = tmpbuf;
else
kfree(tmpbuf);
return ret;
} else if (!is_v3header((size_t) ret, cap->magic_etc)) {
kfree(tmpbuf);
return -EINVAL;
}
nscap = (struct vfs_ns_cap_data *) tmpbuf;
root = le32_to_cpu(nscap->rootid);
kroot = make_kuid(fs_ns, root);
/* If the root kuid maps to a valid uid in current ns, then return
* this as a nscap. */
mappedroot = from_kuid(current_user_ns(), kroot);
if (mappedroot != (uid_t)-1 && mappedroot != (uid_t)0) {
if (alloc) {
*buffer = tmpbuf;
nscap->rootid = cpu_to_le32(mappedroot);
} else
kfree(tmpbuf);
return size;
}
if (!rootid_owns_currentns(kroot)) {
kfree(tmpbuf);
return -EOPNOTSUPP;
}
/* This comes from a parent namespace. Return as a v2 capability */
size = sizeof(struct vfs_cap_data);
if (alloc) {
*buffer = kmalloc(size, GFP_ATOMIC);
if (*buffer) {
struct vfs_cap_data *cap = *buffer;
__le32 nsmagic, magic;
magic = VFS_CAP_REVISION_2;
nsmagic = le32_to_cpu(nscap->magic_etc);
if (nsmagic & VFS_CAP_FLAGS_EFFECTIVE)
magic |= VFS_CAP_FLAGS_EFFECTIVE;
memcpy(&cap->data, &nscap->data, sizeof(__le32) * 2 * VFS_CAP_U32);
cap->magic_etc = cpu_to_le32(magic);
}
}
kfree(tmpbuf);
return size;
}
static kuid_t rootid_from_xattr(const void *value, size_t size,
struct user_namespace *task_ns)
{
const struct vfs_ns_cap_data *nscap = value;
uid_t rootid = 0;
if (size == XATTR_CAPS_SZ_3)
rootid = le32_to_cpu(nscap->rootid);
return make_kuid(task_ns, rootid);
}
static bool validheader(size_t size, __le32 magic)
{
return is_v2header(size, magic) || is_v3header(size, magic);
}
/*
* User requested a write of security.capability. If needed, update the
* xattr to change from v2 to v3, or to fixup the v3 rootid.
*
* If all is ok, we return the new size, on error return < 0.
*/
int cap_convert_nscap(struct dentry *dentry, void **ivalue, size_t size)
{
struct vfs_ns_cap_data *nscap;
uid_t nsrootid;
const struct vfs_cap_data *cap = *ivalue;
__u32 magic, nsmagic;
struct inode *inode = d_backing_inode(dentry);
struct user_namespace *task_ns = current_user_ns(),
*fs_ns = inode->i_sb->s_user_ns;
kuid_t rootid;
size_t newsize;
if (!*ivalue)
return -EINVAL;
if (!validheader(size, cap->magic_etc))
return -EINVAL;
if (!capable_wrt_inode_uidgid(inode, CAP_SETFCAP))
return -EPERM;
if (size == XATTR_CAPS_SZ_2)
if (ns_capable(inode->i_sb->s_user_ns, CAP_SETFCAP))
/* user is privileged, just write the v2 */
return size;
rootid = rootid_from_xattr(*ivalue, size, task_ns);
if (!uid_valid(rootid))
return -EINVAL;
nsrootid = from_kuid(fs_ns, rootid);
if (nsrootid == -1)
return -EINVAL;
newsize = sizeof(struct vfs_ns_cap_data);
nscap = kmalloc(newsize, GFP_ATOMIC);
if (!nscap)
return -ENOMEM;
nscap->rootid = cpu_to_le32(nsrootid);
nsmagic = VFS_CAP_REVISION_3;
magic = le32_to_cpu(cap->magic_etc);
if (magic & VFS_CAP_FLAGS_EFFECTIVE)
nsmagic |= VFS_CAP_FLAGS_EFFECTIVE;
nscap->magic_etc = cpu_to_le32(nsmagic);
memcpy(&nscap->data, &cap->data, sizeof(__le32) * 2 * VFS_CAP_U32);
kvfree(*ivalue);
*ivalue = nscap;
return newsize;
}
/*
* Calculate the new process capability sets from the capability sets attached
* to a file.
*/
static inline int bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data *caps,
struct linux_binprm *bprm,
bool *effective,
bool *has_cap)
{
struct cred *new = bprm->cred;
unsigned i;
int ret = 0;
if (caps->magic_etc & VFS_CAP_FLAGS_EFFECTIVE)
*effective = true;
if (caps->magic_etc & VFS_CAP_REVISION_MASK)
*has_cap = true;
CAP_FOR_EACH_U32(i) {
__u32 permitted = caps->permitted.cap[i];
__u32 inheritable = caps->inheritable.cap[i];
/*
* pP' = (X & fP) | (pI & fI)
* The addition of pA' is handled later.
*/
new->cap_permitted.cap[i] =
(new->cap_bset.cap[i] & permitted) |
(new->cap_inheritable.cap[i] & inheritable);
if (permitted & ~new->cap_permitted.cap[i])
/* insufficient to execute correctly */
ret = -EPERM;
}
/*
* For legacy apps, with no internal support for recognizing they
* do not have enough capabilities, we return an error if they are
* missing some "forced" (aka file-permitted) capabilities.
*/
return *effective ? ret : 0;
}
/*
* Extract the on-exec-apply capability sets for an executable file.
*/
int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps)
{
struct inode *inode = d_backing_inode(dentry);
__u32 magic_etc;
unsigned tocopy, i;
int size;
struct vfs_ns_cap_data data, *nscaps = &data;
struct vfs_cap_data *caps = (struct vfs_cap_data *) &data;
kuid_t rootkuid;
struct user_namespace *fs_ns = inode->i_sb->s_user_ns;
memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data));
if (!inode)
return -ENODATA;
size = __vfs_getxattr((struct dentry *)dentry, inode,
XATTR_NAME_CAPS, &data, XATTR_CAPS_SZ);
if (size == -ENODATA || size == -EOPNOTSUPP)
/* no data, that's ok */
return -ENODATA;
if (size < 0)
return size;
if (size < sizeof(magic_etc))
return -EINVAL;
cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps->magic_etc);
rootkuid = make_kuid(fs_ns, 0);
switch (magic_etc & VFS_CAP_REVISION_MASK) {
case VFS_CAP_REVISION_1:
if (size != XATTR_CAPS_SZ_1)
return -EINVAL;
tocopy = VFS_CAP_U32_1;
break;
case VFS_CAP_REVISION_2:
if (size != XATTR_CAPS_SZ_2)
return -EINVAL;
tocopy = VFS_CAP_U32_2;
break;
case VFS_CAP_REVISION_3:
if (size != XATTR_CAPS_SZ_3)
return -EINVAL;
tocopy = VFS_CAP_U32_3;
rootkuid = make_kuid(fs_ns, le32_to_cpu(nscaps->rootid));
break;
default:
return -EINVAL;
}
/* Limit the caps to the mounter of the filesystem
* or the more limited uid specified in the xattr.
*/
if (!rootid_owns_currentns(rootkuid))
return -ENODATA;
CAP_FOR_EACH_U32(i) {
if (i >= tocopy)
break;
cpu_caps->permitted.cap[i] = le32_to_cpu(caps->data[i].permitted);
cpu_caps->inheritable.cap[i] = le32_to_cpu(caps->data[i].inheritable);
}
cpu_caps->permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
cpu_caps->inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
return 0;
}
/*
* Attempt to get the on-exec apply capability sets for an executable file from
* its xattrs and, if present, apply them to the proposed credentials being
* constructed by execve().
*/
static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_cap)
{
int rc = 0;
struct cpu_vfs_cap_data vcaps;
cap_clear(bprm->cred->cap_permitted);
if (!file_caps_enabled)
return 0;
if (!mnt_may_suid(bprm->file->f_path.mnt))
return 0;
/*
* This check is redundant with mnt_may_suid() but is kept to make
* explicit that capability bits are limited to s_user_ns and its
* descendants.
*/
if (!current_in_userns(bprm->file->f_path.mnt->mnt_sb->s_user_ns))
return 0;
rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);
if (rc < 0) {
if (rc == -EINVAL)
printk(KERN_NOTICE "Invalid argument reading file caps for %s\n",
bprm->filename);
else if (rc == -ENODATA)
rc = 0;
goto out;
}
rc = bprm_caps_from_vfs_caps(&vcaps, bprm, effective, has_cap);
if (rc == -EINVAL)
printk(KERN_NOTICE "%s: cap_from_disk returned %d for %s\n",
__func__, rc, bprm->filename);
out:
if (rc)
cap_clear(bprm->cred->cap_permitted);
return rc;
}
/**
* cap_bprm_set_creds - Set up the proposed credentials for execve().
* @bprm: The execution parameters, including the proposed creds
*
* Set up the proposed credentials for a new execution context being
* constructed by execve(). The proposed creds in @bprm->cred is altered,
* which won't take effect immediately. Returns 0 if successful, -ve on error.
*/
int cap_bprm_set_creds(struct linux_binprm *bprm)
{
const struct cred *old = current_cred();
struct cred *new = bprm->cred;
bool effective, has_cap = false, is_setid;
int ret;
kuid_t root_uid;
if (WARN_ON(!cap_ambient_invariant_ok(old)))
return -EPERM;
effective = false;
ret = get_file_caps(bprm, &effective, &has_cap);
if (ret < 0)
return ret;
root_uid = make_kuid(new->user_ns, 0);
if (!issecure(SECURE_NOROOT)) {
/*
* If the legacy file capability is set, then don't set privs
* for a setuid root binary run by a non-root user. Do set it
* for a root user just to cause least surprise to an admin.
*/
if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
warn_setuid_and_fcaps_mixed(bprm->filename);
goto skip;
}
/*
* To support inheritance of root-permissions and suid-root
* executables under compatibility mode, we override the
* capability sets for the file.
*
* If only the real uid is 0, we do not set the effective bit.
*/
if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) {
/* pP' = (cap_bset & ~0) | (pI & ~0) */
new->cap_permitted = cap_combine(old->cap_bset,
old->cap_inheritable);
}
if (uid_eq(new->euid, root_uid))
effective = true;
}
skip:
/* if we have fs caps, clear dangerous personality flags */
if (!cap_issubset(new->cap_permitted, old->cap_permitted))
bprm->per_clear |= PER_CLEAR_ON_SETID;
/* Don't let someone trace a set[ug]id/setpcap binary with the revised
* credentials unless they have the appropriate permit.
*
* In addition, if NO_NEW_PRIVS, then ensure we get no new privs.
*/
is_setid = !uid_eq(new->euid, old->uid) || !gid_eq(new->egid, old->gid);
if ((is_setid ||
!cap_issubset(new->cap_permitted, old->cap_permitted)) &&
((bprm->unsafe & ~LSM_UNSAFE_PTRACE) ||
!ptracer_capable(current, new->user_ns))) {
/* downgrade; they get no more than they had, and maybe less */
if (!ns_capable(new->user_ns, CAP_SETUID) ||
(bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS)) {
new->euid = new->uid;
new->egid = new->gid;
}
new->cap_permitted = cap_intersect(new->cap_permitted,
old->cap_permitted);
}
new->suid = new->fsuid = new->euid;
new->sgid = new->fsgid = new->egid;
/* File caps or setid cancels ambient. */
if (has_cap || is_setid)
cap_clear(new->cap_ambient);
/*
* Now that we've computed pA', update pP' to give:
* pP' = (X & fP) | (pI & fI) | pA'
*/
new->cap_permitted = cap_combine(new->cap_permitted, new->cap_ambient);
/*
* Set pE' = (fE ? pP' : pA'). Because pA' is zero if fE is set,
* this is the same as pE' = (fE ? pP' : 0) | pA'.
*/
if (effective)
new->cap_effective = new->cap_permitted;
else
new->cap_effective = new->cap_ambient;
if (WARN_ON(!cap_ambient_invariant_ok(new)))
return -EPERM;
/*
* Audit candidate if current->cap_effective is set
*
* We do not bother to audit if 3 things are true:
* 1) cap_effective has all caps
* 2) we are root
* 3) root is supposed to have all caps (SECURE_NOROOT)
* Since this is just a normal root execing a process.
*
* Number 1 above might fail if you don't have a full bset, but I think
* that is interesting information to audit.
*/
if (!cap_issubset(new->cap_effective, new->cap_ambient)) {
if (!cap_issubset(CAP_FULL_SET, new->cap_effective) ||
!uid_eq(new->euid, root_uid) || !uid_eq(new->uid, root_uid) ||
issecure(SECURE_NOROOT)) {
ret = audit_log_bprm_fcaps(bprm, new, old);
if (ret < 0)
return ret;
}
}
new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
if (WARN_ON(!cap_ambient_invariant_ok(new)))
return -EPERM;
/* Check for privilege-elevated exec. */
bprm->cap_elevated = 0;
if (is_setid) {
bprm->cap_elevated = 1;
} else if (!uid_eq(new->uid, root_uid)) {
if (effective ||
!cap_issubset(new->cap_permitted, new->cap_ambient))
bprm->cap_elevated = 1;
}
return 0;
}
/**
* cap_inode_setxattr - Determine whether an xattr may be altered
* @dentry: The inode/dentry being altered
* @name: The name of the xattr to be changed
* @value: The value that the xattr will be changed to
* @size: The size of value
* @flags: The replacement flag
*
* Determine whether an xattr may be altered or set on an inode, returning 0 if
* permission is granted, -ve if denied.
*
* This is used to make sure security xattrs don't get updated or set by those
* who aren't privileged to do so.
*/
int cap_inode_setxattr(struct dentry *dentry, const char *name,
const void *value, size_t size, int flags)
{
/* Ignore non-security xattrs */
if (strncmp(name, XATTR_SECURITY_PREFIX,
sizeof(XATTR_SECURITY_PREFIX) - 1) != 0)
return 0;
/*
* For XATTR_NAME_CAPS the check will be done in
* cap_convert_nscap(), called by setxattr()
*/
if (strcmp(name, XATTR_NAME_CAPS) == 0)
return 0;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
return 0;
}
/**
* cap_inode_removexattr - Determine whether an xattr may be removed
* @dentry: The inode/dentry being altered
* @name: The name of the xattr to be changed
*
* Determine whether an xattr may be removed from an inode, returning 0 if
* permission is granted, -ve if denied.
*
* This is used to make sure security xattrs don't get removed by those who
* aren't privileged to remove them.
*/
int cap_inode_removexattr(struct dentry *dentry, const char *name)
{
/* Ignore non-security xattrs */
if (strncmp(name, XATTR_SECURITY_PREFIX,
sizeof(XATTR_SECURITY_PREFIX) - 1) != 0)
return 0;
if (strcmp(name, XATTR_NAME_CAPS) == 0) {
/* security.capability gets namespaced */
struct inode *inode = d_backing_inode(dentry);
if (!inode)
return -EINVAL;
if (!capable_wrt_inode_uidgid(inode, CAP_SETFCAP))
return -EPERM;
return 0;
}
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
return 0;
}
/*
* cap_emulate_setxuid() fixes the effective / permitted capabilities of
* a process after a call to setuid, setreuid, or setresuid.
*
* 1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of
* {r,e,s}uid != 0, the permitted and effective capabilities are
* cleared.
*
* 2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective
* capabilities of the process are cleared.
*
* 3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective
* capabilities are set to the permitted capabilities.
*
* fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should
* never happen.
*
* -astor
*
* cevans - New behaviour, Oct '99
* A process may, via prctl(), elect to keep its capabilities when it
* calls setuid() and switches away from uid==0. Both permitted and
* effective sets will be retained.
* Without this change, it was impossible for a daemon to drop only some
* of its privilege. The call to setuid(!=0) would drop all privileges!
* Keeping uid 0 is not an option because uid 0 owns too many vital
* files..
* Thanks to Olaf Kirch and Peter Benie for spotting this.
*/
static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old)
{
kuid_t root_uid = make_kuid(old->user_ns, 0);
if ((uid_eq(old->uid, root_uid) ||
uid_eq(old->euid, root_uid) ||
uid_eq(old->suid, root_uid)) &&
(!uid_eq(new->uid, root_uid) &&
!uid_eq(new->euid, root_uid) &&
!uid_eq(new->suid, root_uid))) {
if (!issecure(SECURE_KEEP_CAPS)) {
cap_clear(new->cap_permitted);
cap_clear(new->cap_effective);
}
/*
* Pre-ambient programs expect setresuid to nonroot followed
* by exec to drop capabilities. We should make sure that
* this remains the case.
*/
cap_clear(new->cap_ambient);
}
if (uid_eq(old->euid, root_uid) && !uid_eq(new->euid, root_uid))
cap_clear(new->cap_effective);
if (!uid_eq(old->euid, root_uid) && uid_eq(new->euid, root_uid))
new->cap_effective = new->cap_permitted;
}
/**
* cap_task_fix_setuid - Fix up the results of setuid() call
* @new: The proposed credentials
* @old: The current task's current credentials
* @flags: Indications of what has changed
*
* Fix up the results of setuid() call before the credential changes are
* actually applied, returning 0 to grant the changes, -ve to deny them.
*/
int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags)
{
switch (flags) {
case LSM_SETID_RE:
case LSM_SETID_ID:
case LSM_SETID_RES:
/* juggle the capabilities to follow [RES]UID changes unless
* otherwise suppressed */
if (!issecure(SECURE_NO_SETUID_FIXUP))
cap_emulate_setxuid(new, old);
break;
case LSM_SETID_FS:
/* juggle the capabilties to follow FSUID changes, unless
* otherwise suppressed
*
* FIXME - is fsuser used for all CAP_FS_MASK capabilities?
* if not, we might be a bit too harsh here.
*/
if (!issecure(SECURE_NO_SETUID_FIXUP)) {
kuid_t root_uid = make_kuid(old->user_ns, 0);
if (uid_eq(old->fsuid, root_uid) && !uid_eq(new->fsuid, root_uid))
new->cap_effective =
cap_drop_fs_set(new->cap_effective);
if (!uid_eq(old->fsuid, root_uid) && uid_eq(new->fsuid, root_uid))
new->cap_effective =
cap_raise_fs_set(new->cap_effective,
new->cap_permitted);
}
break;
default:
return -EINVAL;
}
return 0;
}
/*
* Rationale: code calling task_setscheduler, task_setioprio, and
* task_setnice, assumes that
* . if capable(cap_sys_nice), then those actions should be allowed
* . if not capable(cap_sys_nice), but acting on your own processes,
* then those actions should be allowed
* This is insufficient now since you can call code without suid, but
* yet with increased caps.
* So we check for increased caps on the target process.
*/
static int cap_safe_nice(struct task_struct *p)
{
int is_subset, ret = 0;
rcu_read_lock();
is_subset = cap_issubset(__task_cred(p)->cap_permitted,
current_cred()->cap_permitted);
if (!is_subset && !ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE))
ret = -EPERM;
rcu_read_unlock();
return ret;
}
/**
* cap_task_setscheduler - Detemine if scheduler policy change is permitted
* @p: The task to affect
*
* Detemine if the requested scheduler policy change is permitted for the
* specified task, returning 0 if permission is granted, -ve if denied.
*/
int cap_task_setscheduler(struct task_struct *p)
{
return cap_safe_nice(p);
}
/**
* cap_task_ioprio - Detemine if I/O priority change is permitted
* @p: The task to affect
* @ioprio: The I/O priority to set
*
* Detemine if the requested I/O priority change is permitted for the specified
* task, returning 0 if permission is granted, -ve if denied.
*/
int cap_task_setioprio(struct task_struct *p, int ioprio)
{
return cap_safe_nice(p);
}
/**
* cap_task_ioprio - Detemine if task priority change is permitted
* @p: The task to affect
* @nice: The nice value to set
*
* Detemine if the requested task priority change is permitted for the
* specified task, returning 0 if permission is granted, -ve if denied.
*/
int cap_task_setnice(struct task_struct *p, int nice)
{
return cap_safe_nice(p);
}
/*
* Implement PR_CAPBSET_DROP. Attempt to remove the specified capability from
* the current task's bounding set. Returns 0 on success, -ve on error.
*/
static int cap_prctl_drop(unsigned long cap)
{
struct cred *new;
if (!ns_capable(current_user_ns(), CAP_SETPCAP))
return -EPERM;
if (!cap_valid(cap))
return -EINVAL;
new = prepare_creds();
if (!new)
return -ENOMEM;
cap_lower(new->cap_bset, cap);
return commit_creds(new);
}
/**
* cap_task_prctl - Implement process control functions for this security module
* @option: The process control function requested
* @arg2, @arg3, @arg4, @arg5: The argument data for this function
*
* Allow process control functions (sys_prctl()) to alter capabilities; may
* also deny access to other functions not otherwise implemented here.
*
* Returns 0 or +ve on success, -ENOSYS if this function is not implemented
* here, other -ve on error. If -ENOSYS is returned, sys_prctl() and other LSM
* modules will consider performing the function.
*/
int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
unsigned long arg4, unsigned long arg5)
{
const struct cred *old = current_cred();
struct cred *new;
switch (option) {
case PR_CAPBSET_READ:
if (!cap_valid(arg2))
return -EINVAL;
return !!cap_raised(old->cap_bset, arg2);
case PR_CAPBSET_DROP:
return cap_prctl_drop(arg2);
/*
* The next four prctl's remain to assist with transitioning a
* system from legacy UID=0 based privilege (when filesystem
* capabilities are not in use) to a system using filesystem
* capabilities only - as the POSIX.1e draft intended.
*
* Note:
*
* PR_SET_SECUREBITS =
* issecure_mask(SECURE_KEEP_CAPS_LOCKED)
* | issecure_mask(SECURE_NOROOT)
* | issecure_mask(SECURE_NOROOT_LOCKED)
* | issecure_mask(SECURE_NO_SETUID_FIXUP)
* | issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED)
*
* will ensure that the current process and all of its
* children will be locked into a pure
* capability-based-privilege environment.
*/
case PR_SET_SECUREBITS:
if ((((old->securebits & SECURE_ALL_LOCKS) >> 1)
& (old->securebits ^ arg2)) /*[1]*/
|| ((old->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/
|| (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/
|| (cap_capable(current_cred(),
current_cred()->user_ns, CAP_SETPCAP,
SECURITY_CAP_AUDIT) != 0) /*[4]*/
/*
* [1] no changing of bits that are locked
* [2] no unlocking of locks
* [3] no setting of unsupported bits
* [4] doing anything requires privilege (go read about
* the "sendmail capabilities bug")
*/
)
/* cannot change a locked bit */
return -EPERM;
new = prepare_creds();
if (!new)
return -ENOMEM;
new->securebits = arg2;
return commit_creds(new);
case PR_GET_SECUREBITS:
return old->securebits;
case PR_GET_KEEPCAPS:
return !!issecure(SECURE_KEEP_CAPS);
case PR_SET_KEEPCAPS:
if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */
return -EINVAL;
if (issecure(SECURE_KEEP_CAPS_LOCKED))
return -EPERM;
new = prepare_creds();
if (!new)
return -ENOMEM;
if (arg2)
new->securebits |= issecure_mask(SECURE_KEEP_CAPS);
else
new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
return commit_creds(new);
case PR_CAP_AMBIENT:
if (arg2 == PR_CAP_AMBIENT_CLEAR_ALL) {
if (arg3 | arg4 | arg5)
return -EINVAL;
new = prepare_creds();
if (!new)
return -ENOMEM;
cap_clear(new->cap_ambient);
return commit_creds(new);
}
if (((!cap_valid(arg3)) | arg4 | arg5))
return -EINVAL;
if (arg2 == PR_CAP_AMBIENT_IS_SET) {
return !!cap_raised(current_cred()->cap_ambient, arg3);
} else if (arg2 != PR_CAP_AMBIENT_RAISE &&
arg2 != PR_CAP_AMBIENT_LOWER) {
return -EINVAL;
} else {
if (arg2 == PR_CAP_AMBIENT_RAISE &&
(!cap_raised(current_cred()->cap_permitted, arg3) ||
!cap_raised(current_cred()->cap_inheritable,
arg3) ||
issecure(SECURE_NO_CAP_AMBIENT_RAISE)))
return -EPERM;
new = prepare_creds();
if (!new)
return -ENOMEM;
if (arg2 == PR_CAP_AMBIENT_RAISE)
cap_raise(new->cap_ambient, arg3);
else
cap_lower(new->cap_ambient, arg3);
return commit_creds(new);
}
default:
/* No functionality available - continue with default */
return -ENOSYS;
}
}
/**
* cap_vm_enough_memory - Determine whether a new virtual mapping is permitted
* @mm: The VM space in which the new mapping is to be made
* @pages: The size of the mapping
*
* Determine whether the allocation of a new virtual mapping by the current
* task is permitted, returning 1 if permission is granted, 0 if not.
*/
int cap_vm_enough_memory(struct mm_struct *mm, long pages)
{
int cap_sys_admin = 0;
if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN,
SECURITY_CAP_NOAUDIT) == 0)
cap_sys_admin = 1;
return cap_sys_admin;
}
/*
* cap_mmap_addr - check if able to map given addr
* @addr: address attempting to be mapped
*
* If the process is attempting to map memory below dac_mmap_min_addr they need
* CAP_SYS_RAWIO. The other parameters to this function are unused by the
* capability security module. Returns 0 if this mapping should be allowed
* -EPERM if not.
*/
int cap_mmap_addr(unsigned long addr)
{
int ret = 0;
if (addr < dac_mmap_min_addr) {
ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO,
SECURITY_CAP_AUDIT);
/* set PF_SUPERPRIV if it turns out we allow the low mmap */
if (ret == 0)
current->flags |= PF_SUPERPRIV;
}
return ret;
}
int cap_mmap_file(struct file *file, unsigned long reqprot,
unsigned long prot, unsigned long flags)
{
return 0;
}
#ifdef CONFIG_SECURITY
struct security_hook_list capability_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(capable, cap_capable),
LSM_HOOK_INIT(settime, cap_settime),
LSM_HOOK_INIT(ptrace_access_check, cap_ptrace_access_check),
LSM_HOOK_INIT(ptrace_traceme, cap_ptrace_traceme),
LSM_HOOK_INIT(capget, cap_capget),
LSM_HOOK_INIT(capset, cap_capset),
LSM_HOOK_INIT(bprm_set_creds, cap_bprm_set_creds),
LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv),
LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv),
LSM_HOOK_INIT(inode_getsecurity, cap_inode_getsecurity),
LSM_HOOK_INIT(mmap_addr, cap_mmap_addr),
LSM_HOOK_INIT(mmap_file, cap_mmap_file),
LSM_HOOK_INIT(task_fix_setuid, cap_task_fix_setuid),
LSM_HOOK_INIT(task_prctl, cap_task_prctl),
LSM_HOOK_INIT(task_setscheduler, cap_task_setscheduler),
LSM_HOOK_INIT(task_setioprio, cap_task_setioprio),
LSM_HOOK_INIT(task_setnice, cap_task_setnice),
LSM_HOOK_INIT(vm_enough_memory, cap_vm_enough_memory),
};
void __init capability_add_hooks(void)
{
security_add_hooks(capability_hooks, ARRAY_SIZE(capability_hooks),
"capability");
}
#endif /* CONFIG_SECURITY */