linux/security/commoncap.c
Serge E. Hallyn 1f29fae297 file capabilities: add no_file_caps switch (v4)
Add a no_file_caps boot option when file capabilities are
compiled into the kernel (CONFIG_SECURITY_FILE_CAPABILITIES=y).

This allows distributions to ship a kernel with file capabilities
compiled in, without forcing users to use (and understand and
trust) them.

When no_file_caps is specified at boot, then when a process executes
a file, any file capabilities stored with that file will not be
used in the calculation of the process' new capability sets.

This means that booting with the no_file_caps boot option will
not be the same as booting a kernel with file capabilities
compiled out - in particular a task with  CAP_SETPCAP will not
have any chance of passing capabilities to another task (which
isn't "really" possible anyway, and which may soon by killed
altogether by David Howells in any case), and it will instead
be able to put new capabilities in its pI.  However since fI
will always be empty and pI is masked with fI, it gains the
task nothing.

We also support the extra prctl options, setting securebits and
dropping capabilities from the per-process bounding set.

The other remaining difference is that killpriv, task_setscheduler,
setioprio, and setnice will continue to be hooked.  That will
be noticable in the case where a root task changed its uid
while keeping some caps, and another task owned by the new uid
tries to change settings for the more privileged task.

Changelog:
	Nov 05 2008: (v4) trivial port on top of always-start-\
		with-clear-caps patch
	Sep 23 2008: nixed file_caps_enabled when file caps are
		not compiled in as it isn't used.
		Document no_file_caps in kernel-parameters.txt.

Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Andrew G. Morgan <morgan@kernel.org>
Signed-off-by: James Morris <jmorris@namei.org>
2008-11-06 07:14:51 +08:00

715 lines
18 KiB
C

/* Common capabilities, needed by capability.o and root_plug.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/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>
int cap_netlink_send(struct sock *sk, struct sk_buff *skb)
{
NETLINK_CB(skb).eff_cap = current->cap_effective;
return 0;
}
int cap_netlink_recv(struct sk_buff *skb, int cap)
{
if (!cap_raised(NETLINK_CB(skb).eff_cap, cap))
return -EPERM;
return 0;
}
EXPORT_SYMBOL(cap_netlink_recv);
/*
* NOTE WELL: cap_capable() cannot be used like the kernel's capable()
* function. That is, it has the reverse semantics: cap_capable()
* returns 0 when a task has a capability, but the kernel's capable()
* returns 1 for this case.
*/
int cap_capable (struct task_struct *tsk, int cap)
{
/* Derived from include/linux/sched.h:capable. */
if (cap_raised(tsk->cap_effective, cap))
return 0;
return -EPERM;
}
int cap_settime(struct timespec *ts, struct timezone *tz)
{
if (!capable(CAP_SYS_TIME))
return -EPERM;
return 0;
}
int cap_ptrace_may_access(struct task_struct *child, unsigned int mode)
{
/* Derived from arch/i386/kernel/ptrace.c:sys_ptrace. */
if (cap_issubset(child->cap_permitted, current->cap_permitted))
return 0;
if (capable(CAP_SYS_PTRACE))
return 0;
return -EPERM;
}
int cap_ptrace_traceme(struct task_struct *parent)
{
/* Derived from arch/i386/kernel/ptrace.c:sys_ptrace. */
if (cap_issubset(current->cap_permitted, parent->cap_permitted))
return 0;
if (has_capability(parent, CAP_SYS_PTRACE))
return 0;
return -EPERM;
}
int cap_capget (struct task_struct *target, kernel_cap_t *effective,
kernel_cap_t *inheritable, kernel_cap_t *permitted)
{
/* Derived from kernel/capability.c:sys_capget. */
*effective = target->cap_effective;
*inheritable = target->cap_inheritable;
*permitted = target->cap_permitted;
return 0;
}
#ifdef CONFIG_SECURITY_FILE_CAPABILITIES
static inline int cap_block_setpcap(struct task_struct *target)
{
/*
* No support for remote process capability manipulation with
* filesystem capability support.
*/
return (target != current);
}
static inline int cap_inh_is_capped(void)
{
/*
* Return 1 if changes to the inheritable set are limited
* to the old permitted set. That is, if the current task
* does *not* possess the CAP_SETPCAP capability.
*/
return (cap_capable(current, CAP_SETPCAP) != 0);
}
static inline int cap_limit_ptraced_target(void) { return 1; }
#else /* ie., ndef CONFIG_SECURITY_FILE_CAPABILITIES */
static inline int cap_block_setpcap(struct task_struct *t) { return 0; }
static inline int cap_inh_is_capped(void) { return 1; }
static inline int cap_limit_ptraced_target(void)
{
return !capable(CAP_SETPCAP);
}
#endif /* def CONFIG_SECURITY_FILE_CAPABILITIES */
int cap_capset_check (struct task_struct *target, kernel_cap_t *effective,
kernel_cap_t *inheritable, kernel_cap_t *permitted)
{
if (cap_block_setpcap(target)) {
return -EPERM;
}
if (cap_inh_is_capped()
&& !cap_issubset(*inheritable,
cap_combine(target->cap_inheritable,
current->cap_permitted))) {
/* incapable of using this inheritable set */
return -EPERM;
}
if (!cap_issubset(*inheritable,
cap_combine(target->cap_inheritable,
current->cap_bset))) {
/* no new pI capabilities outside bounding set */
return -EPERM;
}
/* verify restrictions on target's new Permitted set */
if (!cap_issubset (*permitted,
cap_combine (target->cap_permitted,
current->cap_permitted))) {
return -EPERM;
}
/* verify the _new_Effective_ is a subset of the _new_Permitted_ */
if (!cap_issubset (*effective, *permitted)) {
return -EPERM;
}
return 0;
}
void cap_capset_set (struct task_struct *target, kernel_cap_t *effective,
kernel_cap_t *inheritable, kernel_cap_t *permitted)
{
target->cap_effective = *effective;
target->cap_inheritable = *inheritable;
target->cap_permitted = *permitted;
}
static inline void bprm_clear_caps(struct linux_binprm *bprm)
{
cap_clear(bprm->cap_post_exec_permitted);
bprm->cap_effective = false;
}
#ifdef CONFIG_SECURITY_FILE_CAPABILITIES
int cap_inode_need_killpriv(struct dentry *dentry)
{
struct inode *inode = dentry->d_inode;
int error;
if (!inode->i_op || !inode->i_op->getxattr)
return 0;
error = inode->i_op->getxattr(dentry, XATTR_NAME_CAPS, NULL, 0);
if (error <= 0)
return 0;
return 1;
}
int cap_inode_killpriv(struct dentry *dentry)
{
struct inode *inode = dentry->d_inode;
if (!inode->i_op || !inode->i_op->removexattr)
return 0;
return inode->i_op->removexattr(dentry, XATTR_NAME_CAPS);
}
static inline int cap_from_disk(struct vfs_cap_data *caps,
struct linux_binprm *bprm, unsigned size)
{
__u32 magic_etc;
unsigned tocopy, i;
int ret;
if (size < sizeof(magic_etc))
return -EINVAL;
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;
}
if (magic_etc & VFS_CAP_FLAGS_EFFECTIVE) {
bprm->cap_effective = true;
} else {
bprm->cap_effective = false;
}
ret = 0;
CAP_FOR_EACH_U32(i) {
__u32 value_cpu;
if (i >= tocopy) {
/*
* Legacy capability sets have no upper bits
*/
bprm->cap_post_exec_permitted.cap[i] = 0;
continue;
}
/*
* pP' = (X & fP) | (pI & fI)
*/
value_cpu = le32_to_cpu(caps->data[i].permitted);
bprm->cap_post_exec_permitted.cap[i] =
(current->cap_bset.cap[i] & value_cpu) |
(current->cap_inheritable.cap[i] &
le32_to_cpu(caps->data[i].inheritable));
if (value_cpu & ~bprm->cap_post_exec_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 bprm->cap_effective ? ret : 0;
}
/* Locate any VFS capabilities: */
static int get_file_caps(struct linux_binprm *bprm)
{
struct dentry *dentry;
int rc = 0;
struct vfs_cap_data vcaps;
struct inode *inode;
bprm_clear_caps(bprm);
if (!file_caps_enabled)
return 0;
if (bprm->file->f_vfsmnt->mnt_flags & MNT_NOSUID)
return 0;
dentry = dget(bprm->file->f_dentry);
inode = dentry->d_inode;
if (!inode->i_op || !inode->i_op->getxattr)
goto out;
rc = inode->i_op->getxattr(dentry, XATTR_NAME_CAPS, &vcaps,
XATTR_CAPS_SZ);
if (rc == -ENODATA || rc == -EOPNOTSUPP) {
/* no data, that's ok */
rc = 0;
goto out;
}
if (rc < 0)
goto out;
rc = cap_from_disk(&vcaps, bprm, rc);
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;
}
#else
int cap_inode_need_killpriv(struct dentry *dentry)
{
return 0;
}
int cap_inode_killpriv(struct dentry *dentry)
{
return 0;
}
static inline int get_file_caps(struct linux_binprm *bprm)
{
bprm_clear_caps(bprm);
return 0;
}
#endif
int cap_bprm_set_security (struct linux_binprm *bprm)
{
int ret;
ret = get_file_caps(bprm);
if (!issecure(SECURE_NOROOT)) {
/*
* 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 (bprm->e_uid == 0 || current->uid == 0) {
/* pP' = (cap_bset & ~0) | (pI & ~0) */
bprm->cap_post_exec_permitted = cap_combine(
current->cap_bset, current->cap_inheritable
);
bprm->cap_effective = (bprm->e_uid == 0);
ret = 0;
}
}
return ret;
}
void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
{
if (bprm->e_uid != current->uid || bprm->e_gid != current->gid ||
!cap_issubset(bprm->cap_post_exec_permitted,
current->cap_permitted)) {
set_dumpable(current->mm, suid_dumpable);
current->pdeath_signal = 0;
if (unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
if (!capable(CAP_SETUID)) {
bprm->e_uid = current->uid;
bprm->e_gid = current->gid;
}
if (cap_limit_ptraced_target()) {
bprm->cap_post_exec_permitted = cap_intersect(
bprm->cap_post_exec_permitted,
current->cap_permitted);
}
}
}
current->suid = current->euid = current->fsuid = bprm->e_uid;
current->sgid = current->egid = current->fsgid = bprm->e_gid;
/* For init, we want to retain the capabilities set
* in the init_task struct. Thus we skip the usual
* capability rules */
if (!is_global_init(current)) {
current->cap_permitted = bprm->cap_post_exec_permitted;
if (bprm->cap_effective)
current->cap_effective = bprm->cap_post_exec_permitted;
else
cap_clear(current->cap_effective);
}
/* AUD: Audit candidate if current->cap_effective is set */
current->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
}
int cap_bprm_secureexec (struct linux_binprm *bprm)
{
if (current->uid != 0) {
if (bprm->cap_effective)
return 1;
if (!cap_isclear(bprm->cap_post_exec_permitted))
return 1;
}
return (current->euid != current->uid ||
current->egid != current->gid);
}
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;
} else if (!strncmp(name, XATTR_SECURITY_PREFIX,
sizeof(XATTR_SECURITY_PREFIX) - 1) &&
!capable(CAP_SYS_ADMIN))
return -EPERM;
return 0;
}
int cap_inode_removexattr(struct dentry *dentry, const char *name)
{
if (!strcmp(name, XATTR_NAME_CAPS)) {
if (!capable(CAP_SETFCAP))
return -EPERM;
return 0;
} else if (!strncmp(name, XATTR_SECURITY_PREFIX,
sizeof(XATTR_SECURITY_PREFIX) - 1) &&
!capable(CAP_SYS_ADMIN))
return -EPERM;
return 0;
}
/* moved from kernel/sys.c. */
/*
* 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 (int old_ruid, int old_euid,
int old_suid)
{
if ((old_ruid == 0 || old_euid == 0 || old_suid == 0) &&
(current->uid != 0 && current->euid != 0 && current->suid != 0) &&
!issecure(SECURE_KEEP_CAPS)) {
cap_clear (current->cap_permitted);
cap_clear (current->cap_effective);
}
if (old_euid == 0 && current->euid != 0) {
cap_clear (current->cap_effective);
}
if (old_euid != 0 && current->euid == 0) {
current->cap_effective = current->cap_permitted;
}
}
int cap_task_post_setuid (uid_t old_ruid, uid_t old_euid, uid_t old_suid,
int flags)
{
switch (flags) {
case LSM_SETID_RE:
case LSM_SETID_ID:
case LSM_SETID_RES:
/* Copied from kernel/sys.c:setreuid/setuid/setresuid. */
if (!issecure (SECURE_NO_SETUID_FIXUP)) {
cap_emulate_setxuid (old_ruid, old_euid, old_suid);
}
break;
case LSM_SETID_FS:
{
uid_t old_fsuid = old_ruid;
/* Copied from kernel/sys.c:setfsuid. */
/*
* 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)) {
if (old_fsuid == 0 && current->fsuid != 0) {
current->cap_effective =
cap_drop_fs_set(
current->cap_effective);
}
if (old_fsuid != 0 && current->fsuid == 0) {
current->cap_effective =
cap_raise_fs_set(
current->cap_effective,
current->cap_permitted);
}
}
break;
}
default:
return -EINVAL;
}
return 0;
}
#ifdef CONFIG_SECURITY_FILE_CAPABILITIES
/*
* 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)
{
if (!cap_issubset(p->cap_permitted, current->cap_permitted) &&
!capable(CAP_SYS_NICE))
return -EPERM;
return 0;
}
int cap_task_setscheduler (struct task_struct *p, int policy,
struct sched_param *lp)
{
return cap_safe_nice(p);
}
int cap_task_setioprio (struct task_struct *p, int ioprio)
{
return cap_safe_nice(p);
}
int cap_task_setnice (struct task_struct *p, int nice)
{
return cap_safe_nice(p);
}
/*
* called from kernel/sys.c for prctl(PR_CABSET_DROP)
* done without task_capability_lock() because it introduces
* no new races - i.e. only another task doing capget() on
* this task could get inconsistent info. There can be no
* racing writer bc a task can only change its own caps.
*/
static long cap_prctl_drop(unsigned long cap)
{
if (!capable(CAP_SETPCAP))
return -EPERM;
if (!cap_valid(cap))
return -EINVAL;
cap_lower(current->cap_bset, cap);
return 0;
}
#else
int cap_task_setscheduler (struct task_struct *p, int policy,
struct sched_param *lp)
{
return 0;
}
int cap_task_setioprio (struct task_struct *p, int ioprio)
{
return 0;
}
int cap_task_setnice (struct task_struct *p, int nice)
{
return 0;
}
#endif
int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
unsigned long arg4, unsigned long arg5, long *rc_p)
{
long error = 0;
switch (option) {
case PR_CAPBSET_READ:
if (!cap_valid(arg2))
error = -EINVAL;
else
error = !!cap_raised(current->cap_bset, arg2);
break;
#ifdef CONFIG_SECURITY_FILE_CAPABILITIES
case PR_CAPBSET_DROP:
error = cap_prctl_drop(arg2);
break;
/*
* 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 ((((current->securebits & SECURE_ALL_LOCKS) >> 1)
& (current->securebits ^ arg2)) /*[1]*/
|| ((current->securebits & SECURE_ALL_LOCKS
& ~arg2)) /*[2]*/
|| (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/
|| (cap_capable(current, CAP_SETPCAP) != 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")
*/
error = -EPERM; /* cannot change a locked bit */
} else {
current->securebits = arg2;
}
break;
case PR_GET_SECUREBITS:
error = current->securebits;
break;
#endif /* def CONFIG_SECURITY_FILE_CAPABILITIES */
case PR_GET_KEEPCAPS:
if (issecure(SECURE_KEEP_CAPS))
error = 1;
break;
case PR_SET_KEEPCAPS:
if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */
error = -EINVAL;
else if (issecure(SECURE_KEEP_CAPS_LOCKED))
error = -EPERM;
else if (arg2)
current->securebits |= issecure_mask(SECURE_KEEP_CAPS);
else
current->securebits &=
~issecure_mask(SECURE_KEEP_CAPS);
break;
default:
/* No functionality available - continue with default */
return 0;
}
/* Functionality provided */
*rc_p = error;
return 1;
}
void cap_task_reparent_to_init (struct task_struct *p)
{
cap_set_init_eff(p->cap_effective);
cap_clear(p->cap_inheritable);
cap_set_full(p->cap_permitted);
p->securebits = SECUREBITS_DEFAULT;
return;
}
int cap_syslog (int type)
{
if ((type != 3 && type != 10) && !capable(CAP_SYS_ADMIN))
return -EPERM;
return 0;
}
int cap_vm_enough_memory(struct mm_struct *mm, long pages)
{
int cap_sys_admin = 0;
if (cap_capable(current, CAP_SYS_ADMIN) == 0)
cap_sys_admin = 1;
return __vm_enough_memory(mm, pages, cap_sys_admin);
}