Commit b5376771 authored by Serge E. Hallyn's avatar Serge E. Hallyn Committed by Linus Torvalds
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Implement file posix capabilities

Implement file posix capabilities.  This allows programs to be given a
subset of root's powers regardless of who runs them, without having to use
setuid and giving the binary all of root's powers.

This version works with Kaigai Kohei's userspace tools, found at  For more information on how to use this
patch, Chris Friedhoff has posted a nice page at

	Nov 27:
	Incorporate fixes from Andrew Morton
	(security-introduce-file-caps-tweaks and
	Fix Kconfig dependency.
	Fix change signaling behavior when file caps are not compiled in.

	Nov 13:
	Integrate comments from Alexey: Remove CONFIG_ ifdef from
	capability.h, and use %zd for printing a size_t.

	Nov 13:
	Fix endianness warnings by sparse as suggested by Alexey

	Nov 09:
	Address warnings of unused variables at cap_bprm_set_security
	when file capabilities are disabled, and simultaneously clean
	up the code a little, by pulling the new code into a helper

	Nov 08:
	For pointers to required userspace tools and how to use
	them, see


	Nov 07:
	Fix the calculation of the highest bit checked in

	Nov 07:
	Allow file caps to be enabled without CONFIG_SECURITY, since
	capabilities are the default.
	Hook cap_task_setscheduler when !CONFIG_SECURITY.
	Move capable(TASK_KILL) to end of cap_task_kill to reduce
	audit messages.

	Nov 05:
	Add secondary calls in selinux/hooks.c to task_setioprio and
	task_setscheduler so that selinux and capabilities with file
	cap support can be stacked.

	Sep 05:
	As Seth Arnold points out, uid checks are out of place
	for capability code.

	Sep 01:
	Define task_setscheduler, task_setioprio, cap_task_kill, and
	task_setnice to make sure a user cannot affect a process in which
	they called a program with some fscaps.

	One remaining question is the note under task_setscheduler: are we
	ok with CAP_SYS_NICE being sufficient to confine a process to a

	It is a semantic change, as without fsccaps, attach_task doesn't
	allow CAP_SYS_NICE to override the uid equivalence check.  But since
	it uses security_task_setscheduler, which elsewhere is used where
	CAP_SYS_NICE can be used to override the uid equivalence check,
	fixing it might be tough.

		 note: this also controls cpuset:attach_task.  Are we ok with
		     CAP_SYS_NICE being used to confine to a cpuset?
		 sys_setpriority uses this (through set_one_prio) for another
		 process.  Need same checks as setrlimit

	Aug 21:
	Updated secureexec implementation to reflect the fact that
	euid and uid might be the same and nonzero, but the process
	might still have elevated caps.

	Aug 15:
	Handle endianness of xattrs.
	Enforce capability version match between kernel and disk.
	Enforce that no bits beyond the known max capability are
	set, else return -EPERM.
	With this extra processing, it may be worth reconsidering
	doing all the work at bprm_set_security rather than

	Aug 10:
	Always call getxattr at bprm_set_security, rather than
	caching it at d_instantiate.

[ file-caps clean up for linux/capability.h]
[ unexport cap_inode_killpriv]
Signed-off-by: default avatarSerge E. Hallyn <>
Cc: Stephen Smalley <>
Cc: James Morris <>
Cc: Chris Wright <>
Cc: Andrew Morgan <>
Signed-off-by: default avatarAndrew Morgan <>
Signed-off-by: default avatarAdrian Bunk <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 57c521ce
......@@ -116,6 +116,15 @@ int notify_change(struct dentry * dentry, struct iattr * attr)
attr->ia_atime = now;
if (!(ia_valid & ATTR_MTIME_SET))
attr->ia_mtime = now;
if (ia_valid & ATTR_KILL_PRIV) {
attr->ia_valid &= ~ATTR_KILL_PRIV;
ia_valid &= ~ATTR_KILL_PRIV;
error = security_inode_need_killpriv(dentry);
if (error > 0)
error = security_inode_killpriv(dentry);
if (error)
return error;
if (ia_valid & ATTR_KILL_SUID) {
attr->ia_valid &= ~ATTR_KILL_SUID;
if (mode & S_ISUID) {
......@@ -368,7 +368,7 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
/* Revoke setuid/setgid bit on chown/chgrp */
if ((iap->ia_valid & ATTR_UID) && iap->ia_uid != inode->i_uid)
iap->ia_valid |= ATTR_KILL_SUID;
iap->ia_valid |= ATTR_KILL_SUID | ATTR_KILL_PRIV;
if ((iap->ia_valid & ATTR_GID) && iap->ia_gid != inode->i_gid)
iap->ia_valid |= ATTR_KILL_SGID;
......@@ -937,7 +937,7 @@ out:
static void kill_suid(struct dentry *dentry)
struct iattr ia;
notify_change(dentry, &ia);
......@@ -658,7 +658,8 @@ static int chown_common(struct dentry * dentry, uid_t user, gid_t group)
newattrs.ia_gid = group;
if (!S_ISDIR(inode->i_mode))
newattrs.ia_valid |= ATTR_KILL_SUID|ATTR_KILL_SGID;
newattrs.ia_valid |=
error = notify_change(dentry, &newattrs);
......@@ -824,13 +824,18 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
struct address_space *mapping = out->f_mapping;
struct inode *inode = mapping->host;
int killsuid, killpriv;
ssize_t ret;
int err;
int err = 0;
err = should_remove_suid(out->f_path.dentry);
if (unlikely(err)) {
killpriv = security_inode_need_killpriv(out->f_path.dentry);
killsuid = should_remove_suid(out->f_path.dentry);
if (unlikely(killsuid || killpriv)) {
err = __remove_suid(out->f_path.dentry, err);
if (killpriv)
err = security_inode_killpriv(out->f_path.dentry);
if (!err && killsuid)
err = __remove_suid(out->f_path.dentry, killsuid);
if (err)
return err;
......@@ -37,7 +37,8 @@ struct linux_binprm{
int sh_bang;
struct file * file;
int e_uid, e_gid;
kernel_cap_t cap_inheritable, cap_permitted, cap_effective;
kernel_cap_t cap_inheritable, cap_permitted;
bool cap_effective;
void *security;
int argc, envc;
char * filename; /* Name of binary as seen by procps */
* This is <linux/capability.h>
* Andrew G. Morgan <>
* Andrew G. Morgan <>
* Alexander Kjeldaas <>
* with help from Aleph1, Roland Buresund and Andrew Main.
* See here for the libcap library ("POSIX draft" compliance):
......@@ -28,23 +28,41 @@ struct task_struct;
following structure to such a composite is better handled in a user
library since the draft standard requires the use of malloc/free
etc.. */
#define _LINUX_CAPABILITY_VERSION 0x19980330
typedef struct __user_cap_header_struct {
__u32 version;
int pid;
} __user *cap_user_header_t;
typedef struct __user_cap_data_struct {
__u32 effective;
__u32 permitted;
__u32 inheritable;
} __user *cap_user_data_t;
#ifdef __KERNEL__
#include <asm/current.h>
#define XATTR_CAPS_SUFFIX "capability"
#define XATTR_CAPS_SZ (3*sizeof(__le32))
#define VFS_CAP_REVISION_MASK 0xFF000000
#define VFS_CAP_REVISION_1 0x01000000
#define VFS_CAP_FLAGS_EFFECTIVE 0x000001
struct vfs_cap_data {
__u32 magic_etc; /* Little endian */
struct {
__u32 permitted; /* Little endian */
__u32 inheritable; /* Little endian */
} data[1];
#ifdef __KERNEL__
......@@ -59,7 +77,7 @@ typedef struct kernel_cap_struct {
typedef __u32 kernel_cap_t;
#define _USER_CAP_HEADER_SIZE (2*sizeof(__u32))
#define _KERNEL_CAP_T_SIZE (sizeof(kernel_cap_t))
......@@ -67,7 +85,7 @@ typedef __u32 kernel_cap_t;
** POSIX-draft defined capabilities.
** POSIX-draft defined capabilities.
/* In a system with the [_POSIX_CHOWN_RESTRICTED] option defined, this
......@@ -87,7 +105,7 @@ typedef __u32 kernel_cap_t;
defined. Excluding DAC access covered by CAP_LINUX_IMMUTABLE. */
/* Overrides all restrictions about allowed operations on files, where
file owner ID must be equal to the user ID, except where CAP_FSETID
is applicable. It doesn't override MAC and DAC restrictions. */
......@@ -257,7 +275,7 @@ typedef __u32 kernel_cap_t;
/* Override reserved space on ext2 filesystem */
/* Modify data journaling mode on ext3 filesystem (uses journaling
resources) */
/* NOTE: ext2 honors fsuid when checking for resource overrides, so
/* NOTE: ext2 honors fsuid when checking for resource overrides, so
you can override using fsuid too */
/* Override size restrictions on IPC message queues */
/* Allow more than 64hz interrupts from the real-time clock */
......@@ -289,8 +307,10 @@ typedef __u32 kernel_cap_t;
#define CAP_SETFCAP 31
#ifdef __KERNEL__
* Bounding set
extern kernel_cap_t cap_bset;
......@@ -298,7 +318,7 @@ extern kernel_cap_t cap_bset;
* Internal kernel functions only
#define to_cap_t(x) { x }
......@@ -329,6 +329,7 @@ typedef void (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
#define ATTR_KILL_SUID 2048
#define ATTR_KILL_SGID 4096
#define ATTR_FILE 8192
#define ATTR_KILL_PRIV 16384
* This is the Inode Attributes structure, used for notify_change(). It
......@@ -51,8 +51,14 @@ extern void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe);
extern int cap_bprm_secureexec(struct linux_binprm *bprm);
extern int cap_inode_setxattr(struct dentry *dentry, char *name, void *value, size_t size, int flags);
extern int cap_inode_removexattr(struct dentry *dentry, char *name);
extern int cap_inode_need_killpriv(struct dentry *dentry);
extern int cap_inode_killpriv(struct dentry *dentry);
extern int cap_task_post_setuid (uid_t old_ruid, uid_t old_euid, uid_t old_suid, int flags);
extern void cap_task_reparent_to_init (struct task_struct *p);
extern int cap_task_kill(struct task_struct *p, struct siginfo *info, int sig, u32 secid);
extern int cap_task_setscheduler (struct task_struct *p, int policy, struct sched_param *lp);
extern int cap_task_setioprio (struct task_struct *p, int ioprio);
extern int cap_task_setnice (struct task_struct *p, int nice);
extern int cap_syslog (int type);
extern int cap_vm_enough_memory(struct mm_struct *mm, long pages);
......@@ -413,6 +419,18 @@ struct request_sock;
* is specified by @buffer_size. @buffer may be NULL to request
* the size of the buffer required.
* Returns number of bytes used/required on success.
* @inode_need_killpriv:
* Called when an inode has been changed.
* @dentry is the dentry being changed.
* Return <0 on error to abort the inode change operation.
* Return 0 if inode_killpriv does not need to be called.
* Return >0 if inode_killpriv does need to be called.
* @inode_killpriv:
* The setuid bit is being removed. Remove similar security labels.
* Called with the dentry->d_inode->i_mutex held.
* @dentry is the dentry being changed.
* Return 0 on success. If error is returned, then the operation
* causing setuid bit removal is failed.
* Security hooks for file operations
......@@ -1239,6 +1257,8 @@ struct security_operations {
int (*inode_getxattr) (struct dentry *dentry, char *name);
int (*inode_listxattr) (struct dentry *dentry);
int (*inode_removexattr) (struct dentry *dentry, char *name);
int (*inode_need_killpriv) (struct dentry *dentry);
int (*inode_killpriv) (struct dentry *dentry);
const char *(*inode_xattr_getsuffix) (void);
int (*inode_getsecurity)(const struct inode *inode, const char *name, void *buffer, size_t size, int err);
int (*inode_setsecurity)(struct inode *inode, const char *name, const void *value, size_t size, int flags);
......@@ -1496,6 +1516,8 @@ void security_inode_post_setxattr(struct dentry *dentry, char *name,
int security_inode_getxattr(struct dentry *dentry, char *name);
int security_inode_listxattr(struct dentry *dentry);
int security_inode_removexattr(struct dentry *dentry, char *name);
int security_inode_need_killpriv(struct dentry *dentry);
int security_inode_killpriv(struct dentry *dentry);
const char *security_inode_xattr_getsuffix(void);
int security_inode_getsecurity(const struct inode *inode, const char *name, void *buffer, size_t size, int err);
int security_inode_setsecurity(struct inode *inode, const char *name, const void *value, size_t size, int flags);
......@@ -1891,6 +1913,16 @@ static inline int security_inode_removexattr (struct dentry *dentry, char *name)
return cap_inode_removexattr(dentry, name);
static inline int security_inode_need_killpriv(struct dentry *dentry)
return cap_inode_need_killpriv(dentry);
static inline int security_inode_killpriv(struct dentry *dentry)
return cap_inode_killpriv(dentry);
static inline const char *security_inode_xattr_getsuffix (void)
return NULL ;
......@@ -2035,12 +2067,12 @@ static inline int security_task_setgroups (struct group_info *group_info)
static inline int security_task_setnice (struct task_struct *p, int nice)
return 0;
return cap_task_setnice(p, nice);
static inline int security_task_setioprio (struct task_struct *p, int ioprio)
return 0;
return cap_task_setioprio(p, ioprio);
static inline int security_task_getioprio (struct task_struct *p)
......@@ -2058,7 +2090,7 @@ static inline int security_task_setscheduler (struct task_struct *p,
int policy,
struct sched_param *lp)
return 0;
return cap_task_setscheduler(p, policy, lp);
static inline int security_task_getscheduler (struct task_struct *p)
......@@ -2075,7 +2107,7 @@ static inline int security_task_kill (struct task_struct *p,
struct siginfo *info, int sig,
u32 secid)
return 0;
return cap_task_kill(p, info, sig, secid);
static inline int security_task_wait (struct task_struct *p)
......@@ -1627,12 +1627,18 @@ int __remove_suid(struct dentry *dentry, int kill)
int remove_suid(struct dentry *dentry)
int kill = should_remove_suid(dentry);
int killsuid = should_remove_suid(dentry);
int killpriv = security_inode_need_killpriv(dentry);
int error = 0;
if (unlikely(kill))
return __remove_suid(dentry, kill);
if (killpriv < 0)
return killpriv;
if (killpriv)
error = security_inode_killpriv(dentry);
if (!error && killsuid)
error = __remove_suid(dentry, killsuid);
return 0;
return error;
......@@ -80,6 +80,16 @@ config SECURITY_CAPABILITIES
This enables the "default" Linux capabilities functionality.
If you are unsure how to answer this question, answer Y.
bool "File POSIX Capabilities (EXPERIMENTAL)"
default n
This enables filesystem capabilities, allowing you to give
binaries a subset of root's powers without using setuid 0.
If in doubt, answer N.
bool "Root Plug Support"
depends on USB=y && SECURITY
......@@ -37,7 +37,13 @@ static struct security_operations capability_ops = {
.inode_setxattr = cap_inode_setxattr,
.inode_removexattr = cap_inode_removexattr,
.inode_need_killpriv = cap_inode_need_killpriv,
.inode_killpriv = cap_inode_killpriv,
.task_kill = cap_task_kill,
.task_setscheduler = cap_task_setscheduler,
.task_setioprio = cap_task_setioprio,
.task_setnice = cap_task_setnice,
.task_post_setuid = cap_task_post_setuid,
.task_reparent_to_init = cap_task_reparent_to_init,
......@@ -22,6 +22,7 @@
#include <linux/ptrace.h>
#include <linux/xattr.h>
#include <linux/hugetlb.h>
#include <linux/mount.h>
int cap_netlink_send(struct sock *sk, struct sk_buff *skb)
......@@ -108,14 +109,130 @@ void cap_capset_set (struct task_struct *target, kernel_cap_t *effective,
target->cap_permitted = *permitted;
static inline void bprm_clear_caps(struct linux_binprm *bprm)
bprm->cap_effective = false;
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(__le32 *caps, struct linux_binprm *bprm,
int size)
__u32 magic_etc;
if (size != XATTR_CAPS_SZ)
return -EINVAL;
magic_etc = le32_to_cpu(caps[0]);
switch ((magic_etc & VFS_CAP_REVISION_MASK)) {
if (magic_etc & VFS_CAP_FLAGS_EFFECTIVE)
bprm->cap_effective = true;
bprm->cap_effective = false;
bprm->cap_permitted = to_cap_t( le32_to_cpu(caps[1]) );
bprm->cap_inheritable = to_cap_t( le32_to_cpu(caps[2]) );
return 0;
return -EINVAL;
/* Locate any VFS capabilities: */
static int get_file_caps(struct linux_binprm *bprm)
struct dentry *dentry;
int rc = 0;
__le32 v1caps[XATTR_CAPS_SZ];
struct inode *inode;
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, &v1caps,
if (rc == -ENODATA || rc == -EOPNOTSUPP) {
/* no data, that's ok */
rc = 0;
goto out;
if (rc < 0)
goto out;
rc = cap_from_disk(v1caps, bprm, rc);
if (rc)
printk(KERN_NOTICE "%s: cap_from_disk returned %d for %s\n",
__FUNCTION__, rc, bprm->filename);
if (rc)
return rc;
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)
return 0;
int cap_bprm_set_security (struct linux_binprm *bprm)
/* Copied from fs/exec.c:prepare_binprm. */
int ret;
/* We don't have VFS support for capabilities yet */
cap_clear (bprm->cap_inheritable);
cap_clear (bprm->cap_permitted);
cap_clear (bprm->cap_effective);
ret = get_file_caps(bprm);
if (ret)
printk(KERN_NOTICE "%s: get_file_caps returned %d for %s\n",
__FUNCTION__, ret, bprm->filename);
/* To support inheritance of root-permissions and suid-root
* executables under compatibility mode, we raise all three
......@@ -131,9 +248,10 @@ int cap_bprm_set_security (struct linux_binprm *bprm)
cap_set_full (bprm->cap_permitted);
if (bprm->e_uid == 0)
cap_set_full (bprm->cap_effective);
bprm->cap_effective = true;
return 0;
return ret;
void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
......@@ -149,6 +267,7 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
if (bprm->e_uid != current->uid || bprm->e_gid != current->gid ||
!cap_issubset (new_permitted, current->cap_permitted)) {
set_dumpable(current->mm, suid_dumpable);
current->pdeath_signal = 0;
if (unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
if (!capable(CAP_SETUID)) {
......@@ -170,8 +289,8 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
* capability rules */
if (!is_init(current)) {
current->cap_permitted = new_permitted;
current->cap_effective =
cap_intersect (new_permitted, bprm->cap_effective);
current->cap_effective = bprm->cap_effective ?
new_permitted : 0;
/* AUD: Audit candidate if current->cap_effective is set */
......@@ -181,11 +300,15 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
int cap_bprm_secureexec (struct linux_binprm *bprm)
/* If/when this module is enhanced to incorporate capability
bits on files, the test below should be extended to also perform a
test between the old and new capability sets. For now,
it simply preserves the legacy decision algorithm used by
the old userland. */
if (current->uid != 0) {
if (bprm->cap_effective)
return 1;
if (!cap_isclear(bprm->cap_permitted))
return 1;
if (!cap_isclear(bprm->cap_inheritable))
return 1;
return (current->euid != current->uid ||
current->egid != current->gid);
......@@ -193,7 +316,11 @@ int cap_bprm_secureexec (struct linux_binprm *bprm)
int cap_inode_setxattr(struct dentry *dentry, char *name, void *value,
size_t size, int flags)
if (!strncmp(name, XATTR_SECURITY_PREFIX,
if (!strcmp(name, XATTR_NAME_CAPS)) {
if (!capable(CAP_SETFCAP))
return -EPERM;
return 0;
} else if (!strncmp(name, XATTR_SECURITY_PREFIX,
return -EPERM;
......@@ -202,7 +329,11 @@ int cap_inode_setxattr(struct dentry *dentry, char *name, void *value,
int cap_inode_removexattr(struct dentry *dentry, char *name)
if (!strncmp(name, XATTR_SECURITY_PREFIX,
if (!strcmp(name, XATTR_NAME_CAPS)) {
if (!capable(CAP_SETFCAP))
return -EPERM;
return 0;
} else if (!strncmp(name, XATTR_SECURITY_PREFIX,
return -EPERM;
......@@ -299,6 +430,83 @@ int cap_task_post_setuid (uid_t old_ruid, uid_t old_euid, uid_t old_suid,
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 inline int cap_safe_nice(struct task_struct *p)
if (!cap_issubset(p->cap_permitted, current->cap_permitted) &&
!__capable(current, 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);
int cap_task_kill(struct task_struct *p, struct siginfo *info,
int sig, u32 secid)