Relax si_code check in rt_sigqueueinfo and rt_tgsigqueueinfoHEADmaster

commit 243b422af9ea9af4ead07a8ad54c90d4f9b6081a upstream

Commit da48524eb206 ("Prevent rt_sigqueueinfo and rt_tgsigqueueinfo
from spoofing the signal code") made the check on si_code too strict.
There are several legitimate places where glibc wants to queue a
negative si_code different from SI_QUEUE:

 - This was first noticed with glibc's aio implementation, which wants
   to queue a signal with si_code SI_ASYNCIO; the current kernel
   causes glibc's tst-aio4 test to fail because rt_sigqueueinfo()
   fails with EPERM.

 - Further examination of the glibc source shows that getaddrinfo_a()
   wants to use SI_ASYNCNL (which the kernel does not even define).
   The timer_create() fallback code wants to queue signals with SI_TIMER.

As suggested by Oleg Nesterov <oleg@redhat.com>, loosen the check to
forbid only the problematic SI_TKILL case.

Reported-by: Klaus Dittrich <kladit@arcor.de>
Acked-by: Julien Tinnes <jln@google.com>
Cc: <stable@kernel.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Tested-by: Krzysztof Mazur <krzysiek@podlesie.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>

1 files changed, 1 insertions, 1 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index b368505a7b22fc..461885de3ff24d 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1076,7 +1076,7 @@ sys_rt_sigqueueinfo(int pid, int sig, siginfo_t *uinfo)
 	/* Not even root can pretend to send signals from the kernel.
 	 * Nor can they impersonate a kill()/tgkill(), which adds source info.
 	 */
-	if (info.si_code != SI_QUEUE) {
+	if (info.si_code >= 0 || info.si_code == SI_TKILL) {
 		/* We used to allow any < 0 si_code */
 		return -EPERM;
 	}