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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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40
security/commoncap.c
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@@ -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)