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Commit da48524e authored by Julien Tinnes's avatar Julien Tinnes Committed by Linus Torvalds
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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: default avatarJulien Tinnes <jln@google.com>
Acked-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b52307ca

kernel/signal.c

+12 −4
Original line number Diff line number Diff line
@@ -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);