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Subject[PATCH] [226/275] Prevent rt_sigqueueinfo and rt_tgsigqueueinfo from spoofing the signal code
Date
2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Julien Tinnes <jln@google.com>

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@google.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

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

Index: linux-2.6.35.y/kernel/signal.c
===================================================================
--- linux-2.6.35.y.orig/kernel/signal.c 2011-03-29 22:50:25.616602954 -0700
+++ linux-2.6.35.y/kernel/signal.c 2011-03-29 23:03:02.941224912 -0700
@@ -2410,9 +2410,13 @@
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. */
@@ -2426,9 +2430,13 @@
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);

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