[PATCH 104/173] Prevent rt_sigqueueinfo and rt_tgsigqueueinfo from spoofing the signal code

[Willy Tarreau]

2.6.27.59-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Julien Tinnes <jln@xxxxxxxxxx>

commit da48524eb20662618854bb3df2db01fc65f3070c upstream.

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@xxxxxxxxxx>
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
[wt: 2.6.27 does not have do_rt_tgsigqueueinfo()]

---
 kernel/signal.c |   16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

Index: longterm-2.6.27/kernel/signal.c
===================================================================
--- longterm-2.6.27.orig/kernel/signal.c	2011-01-23 10:52:37.000000000 +0100
+++ longterm-2.6.27/kernel/signal.c	2011-04-25 16:06:27.491278774 +0200
@@ -2294,9 +2294,13 @@
 		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.  */


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