kernel-ark/security/commoncap.c
Eric Paris 7d8b6c6375 CAPABILITIES: remove undefined caps from all processes
This is effectively a revert of 7b9a7ec565
plus fixing it a different way...

We found, when trying to run an application from an application which
had dropped privs that the kernel does security checks on undefined
capability bits.  This was ESPECIALLY difficult to debug as those
undefined bits are hidden from /proc/$PID/status.

Consider a root application which drops all capabilities from ALL 4
capability sets.  We assume, since the application is going to set
eff/perm/inh from an array that it will clear not only the defined caps
less than CAP_LAST_CAP, but also the higher 28ish bits which are
undefined future capabilities.

The BSET gets cleared differently.  Instead it is cleared one bit at a
time.  The problem here is that in security/commoncap.c::cap_task_prctl()
we actually check the validity of a capability being read.  So any task
which attempts to 'read all things set in bset' followed by 'unset all
things set in bset' will not even attempt to unset the undefined bits
higher than CAP_LAST_CAP.

So the 'parent' will look something like:
CapInh:	0000000000000000
CapPrm:	0000000000000000
CapEff:	0000000000000000
CapBnd:	ffffffc000000000

All of this 'should' be fine.  Given that these are undefined bits that
aren't supposed to have anything to do with permissions.  But they do...

So lets now consider a task which cleared the eff/perm/inh completely
and cleared all of the valid caps in the bset (but not the invalid caps
it couldn't read out of the kernel).  We know that this is exactly what
the libcap-ng library does and what the go capabilities library does.
They both leave you in that above situation if you try to clear all of
you capapabilities from all 4 sets.  If that root task calls execve()
the child task will pick up all caps not blocked by the bset.  The bset
however does not block bits higher than CAP_LAST_CAP.  So now the child
task has bits in eff which are not in the parent.  These are
'meaningless' undefined bits, but still bits which the parent doesn't
have.

The problem is now in cred_cap_issubset() (or any operation which does a
subset test) as the child, while a subset for valid cap bits, is not a
subset for invalid cap bits!  So now we set durring commit creds that
the child is not dumpable.  Given it is 'more priv' than its parent.  It
also means the parent cannot ptrace the child and other stupidity.

The solution here:
1) stop hiding capability bits in status
	This makes debugging easier!

2) stop giving any task undefined capability bits.  it's simple, it you
don't put those invalid bits in CAP_FULL_SET you won't get them in init
and you won't get them in any other task either.
	This fixes the cap_issubset() tests and resulting fallout (which
	made the init task in a docker container untraceable among other
	things)

3) mask out undefined bits when sys_capset() is called as it might use
~0, ~0 to denote 'all capabilities' for backward/forward compatibility.
	This lets 'capsh --caps="all=eip" -- -c /bin/bash' run.

4) mask out undefined bit when we read a file capability off of disk as
again likely all bits are set in the xattr for forward/backward
compatibility.
	This lets 'setcap all+pe /bin/bash; /bin/bash' run

Signed-off-by: Eric Paris <eparis@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Andrew Vagin <avagin@openvz.org>
Cc: Andrew G. Morgan <morgan@kernel.org>
Cc: Serge E. Hallyn <serge.hallyn@canonical.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Steve Grubb <sgrubb@redhat.com>
Cc: Dan Walsh <dwalsh@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: James Morris <james.l.morris@oracle.com>
2014-07-24 21:53:47 +10:00

988 lines
28 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/security.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;
}
}
int cap_netlink_send(struct sock *sk, struct sk_buff *skb)
{
return 0;
}
/**
* 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;
/* Have we tried all of the parent namespaces? */
if (ns == &init_user_ns)
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 timespec *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;
rcu_read_lock();
cred = current_cred();
child_cred = __task_cred(child);
if (cred->user_ns == child_cred->user_ns &&
cap_issubset(child_cred->cap_permitted, cred->cap_permitted))
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;
return 0;
}
/*
* Clear proposed capability sets for execve().
*/
static inline void bprm_clear_caps(struct linux_binprm *bprm)
{
cap_clear(bprm->cred->cap_permitted);
bprm->cap_effective = false;
}
/**
* 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 = dentry->d_inode;
int error;
if (!inode->i_op->getxattr)
return 0;
error = inode->i_op->getxattr(dentry, XATTR_NAME_CAPS, NULL, 0);
if (error <= 0)
return 0;
return 1;
}
/**
* 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)
{
struct inode *inode = dentry->d_inode;
if (!inode->i_op->removexattr)
return 0;
return inode->i_op->removexattr(dentry, XATTR_NAME_CAPS);
}
/*
* 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)
*/
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 = dentry->d_inode;
__u32 magic_etc;
unsigned tocopy, i;
int size;
struct vfs_cap_data caps;
memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data));
if (!inode || !inode->i_op->getxattr)
return -ENODATA;
size = inode->i_op->getxattr((struct dentry *)dentry, XATTR_NAME_CAPS, &caps,
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);
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;
default:
return -EINVAL;
}
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)
{
struct dentry *dentry;
int rc = 0;
struct cpu_vfs_cap_data vcaps;
bprm_clear_caps(bprm);
if (!file_caps_enabled)
return 0;
if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
return 0;
dentry = dget(bprm->file->f_dentry);
rc = get_vfs_caps_from_disk(dentry, &vcaps);
if (rc < 0) {
if (rc == -EINVAL)
printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n",
__func__, rc, 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:
dput(dentry);
if (rc)
bprm_clear_caps(bprm);
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;
int ret;
kuid_t root_uid;
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.
*/
if ((!uid_eq(new->euid, old->uid) ||
!gid_eq(new->egid, old->gid) ||
!cap_issubset(new->cap_permitted, old->cap_permitted)) &&
bprm->unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
/* downgrade; they get no more than they had, and maybe less */
if (!capable(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;
if (effective)
new->cap_effective = new->cap_permitted;
else
cap_clear(new->cap_effective);
bprm->cap_effective = effective;
/*
* 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_isclear(new->cap_effective)) {
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);
return 0;
}
/**
* cap_bprm_secureexec - Determine whether a secure execution is required
* @bprm: The execution parameters
*
* Determine whether a secure execution is required, return 1 if it is, and 0
* if it is not.
*
* The credentials have been committed by this point, and so are no longer
* available through @bprm->cred.
*/
int cap_bprm_secureexec(struct linux_binprm *bprm)
{
const struct cred *cred = current_cred();
kuid_t root_uid = make_kuid(cred->user_ns, 0);
if (!uid_eq(cred->uid, root_uid)) {
if (bprm->cap_effective)
return 1;
if (!cap_isclear(cred->cap_permitted))
return 1;
}
return (!uid_eq(cred->euid, cred->uid) ||
!gid_eq(cred->egid, cred->gid));
}
/**
* 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)
{
if (!strcmp(name, XATTR_NAME_CAPS)) {
if (!capable(CAP_SETFCAP))
return -EPERM;
return 0;
}
if (!strncmp(name, XATTR_SECURITY_PREFIX,
sizeof(XATTR_SECURITY_PREFIX) - 1) &&
!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)
{
if (!strcmp(name, XATTR_NAME_CAPS)) {
if (!capable(CAP_SETFCAP))
return -EPERM;
return 0;
}
if (!strncmp(name, XATTR_SECURITY_PREFIX,
sizeof(XATTR_SECURITY_PREFIX) - 1) &&
!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)) &&
!issecure(SECURE_KEEP_CAPS)) {
cap_clear(new->cap_permitted);
cap_clear(new->cap_effective);
}
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);
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 0 if permission is granted, -ve 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 __vm_enough_memory(mm, pages, 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;
}