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file capabilities: remove cap_task_kill()

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The original justification for cap_task_kill() was as follows:

	check_kill_permission() does appropriate uid equivalence checks.
	However with file capabilities it becomes possible for an
	unprivileged user to execute a file with file capabilities
	resulting in a more privileged task with the same uid.

However now that cap_task_kill() always returns 0 (permission
granted) when p->uid==current->uid, the whole hook is worthless,
and only likely to create more subtle problems in the corner cases
where it might still be called but return -EPERM.  Those cases
are basically when uids are different but euid/suid is equivalent
as per the check in check_kill_permission().

One example of a still-broken application is 'at' for non-root users.

This patch removes cap_task_kill().

Signed-off-by: Serge Hallyn <serge@hallyn.com>
Acked-by: Andrew G. Morgan <morgan@kernel.org>
Earlier-version-tested-by: Luiz Fernando N. Capitulino <lcapitulino@mandriva.com.br>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Serge Hallyn 2008-02-29 15:14:57 +00:00 committed by Linus Torvalds
parent 457fb60583
commit aedb60a67c
4 changed files with 1 additions and 48 deletions
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3
include/linux/security.h
View file

@ -57,7 +57,6 @@ 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);
@ -2187,7 +2186,7 @@ static inline int security_task_kill (struct task_struct *p,
struct siginfo *info, int sig,
u32 secid)
{
return cap_task_kill(p, info, sig, secid);
return 0;
}
static inline int security_task_wait (struct task_struct *p)

1
security/capability.c
View file

@ -40,7 +40,6 @@ static struct security_operations capability_ops = {
.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,

40
security/commoncap.c
View file

@ -540,41 +540,6 @@ 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)
{
if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info)))
return 0;
/*
* Running a setuid root program raises your capabilities.
* Killing your own setuid root processes was previously
* allowed.
* We must preserve legacy signal behavior in this case.
*/
if (p->uid == current->uid)
return 0;
/* sigcont is permitted within same session */
if (sig == SIGCONT && (task_session_nr(current) == task_session_nr(p)))
return 0;
if (secid)
/*
* Signal sent as a particular user.
* Capabilities are ignored. May be wrong, but it's the
* only thing we can do at the moment.
* Used only by usb drivers?
*/
return 0;
if (cap_issubset(p->cap_permitted, current->cap_permitted))
return 0;
if (capable(CAP_KILL))
return 0;
return -EPERM;
}
/*
* called from kernel/sys.c for prctl(PR_CABSET_DROP)
* done without task_capability_lock() because it introduces
@ -605,11 +570,6 @@ int cap_task_setnice (struct task_struct *p, int nice)
{
return 0;
}
int cap_task_kill(struct task_struct *p, struct siginfo *info,
int sig, u32 secid)
{
return 0;
}
#endif
void cap_task_reparent_to_init (struct task_struct *p)

5
security/smack/smack_lsm.c
View file

@ -1117,11 +1117,6 @@ static int smack_task_movememory(struct task_struct *p)
static int smack_task_kill(struct task_struct *p, struct siginfo *info,
int sig, u32 secid)
{
int rc;
rc = cap_task_kill(p, info, sig, secid);
if (rc != 0)
return rc;
/*
* Special cases where signals really ought to go through
* in spite of policy. Stephen Smalley suggests it may