Fix signalfd interaction with thread-private signals

Don't let signalfd dequeue private signals off other threads (in the
case of things like SIGILL or SIGSEGV, trying to do so would result
in undefined behaviour on who actually gets the signal, since they
are force unblocked).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index fe590e00db8d..f9405609774e 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -363,7 +363,13 @@ static int __dequeue_signal(struct sigpending *pending, sigset_t *mask,
  */
 int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
 {
-        int signr = __dequeue_signal(&tsk->pending, mask, info);
+        int signr = 0;
+
+        /* We only dequeue private signals from ourselves, we don't let
+         * signalfd steal them
+         */
+        if (tsk == current)
+                signr = __dequeue_signal(&tsk->pending, mask, info);
         if (!signr) {
                 signr = __dequeue_signal(&tsk->signal->shared_pending,
                                          mask, info);