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Prevent rt_sigqueueinfo and rt_tgsigqueueinfo from spoofing the signal code 

Userland should be able to trust the pid and uid of the sender of a
signal if the si_code is SI_TKILL.

Unfortunately, the kernel has historically allowed sigqueueinfo() to
send any si_code at all (as long as it was negative - to distinguish it
from kernel-generated signals like SIGILL etc), so it could spoof a
SI_TKILL with incorrect siginfo values.

Happily, it looks like glibc has always set si_code to the appropriate
SI_QUEUE, so there are probably no actual user code that ever uses
anything but the appropriate SI_QUEUE flag.

So just tighten the check for si_code (we used to allow any negative
value), and add a (one-time) warning in case there are binaries out
there that might depend on using other si_code values.

Signed-off-by: Julien Tinnes <jln@google.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Julien Tinnes 2011-03-18 15:05:21 -07:00 committed by Linus Torvalds
parent b52307ca14
commit da48524eb2
1 changed files with 12 additions and 4 deletions
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16
kernel/signal.c
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@ -2421,9 +2421,13 @@ SYSCALL_DEFINE3(rt_sigqueueinfo, pid_t, pid, int, sig,
return -EFAULT;
/* Not even root can pretend to send signals from the kernel.
Nor can they impersonate a kill(), which adds source info. */
if (info.si_code >= 0)
* Nor can they impersonate a kill()/tgkill(), which adds source info.
*/
if (info.si_code != SI_QUEUE) {
/* We used to allow any < 0 si_code */
WARN_ON_ONCE(info.si_code < 0);
return -EPERM;
}
info.si_signo = sig;
/* POSIX.1b doesn't mention process groups. */
@ -2437,9 +2441,13 @@ long do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig, siginfo_t *info)
return -EINVAL;
/* Not even root can pretend to send signals from the kernel.
Nor can they impersonate a kill(), which adds source info. */
if (info->si_code >= 0)
* Nor can they impersonate a kill()/tgkill(), which adds source info.
*/
if (info->si_code != SI_QUEUE) {
/* We used to allow any < 0 si_code */
WARN_ON_ONCE(info->si_code < 0);
return -EPERM;
}
info->si_signo = sig;
return do_send_specific(tgid, pid, sig, info);