Relax si_code check in rt_sigqueueinfo and rt_tgsigqueueinfo

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>
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
[wt: 2.6.27 has no rt_tgsigqueueinfo()]

diff --git a/kernel/signal.c b/kernel/signal.c
index 56d815dea38d0c9622ca324ddab6c6b26f55b573..b1506fb1d74135752978ea3deac2b5b6ad15c123 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2296,7 +2296,7 @@ SYSCALL_DEFINE3(rt_sigqueueinfo, pid_t, pid, int, sig,
        /* 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 */
                WARN_ON_ONCE(info.si_code < 0);
                return -EPERM;