[PATCH] signal: skip blocked signals in dequeue_synchronous_signal()

[Avi Weiss <thnkslprpt@gmail.com>]

dequeue_synchronous_signal() checks whether an unblocked
synchronous signal is pending, but its queue scan can select a
different blocked entry with a positive si_code. This can deliver
a signal while it is still blocked.

Check the blocked mask for each queued entry. Forced faults
are unblocked when necessary by force_sig_info_to_task(), and the
existing pending bookkeeping is unchanged.

Fixes: 7146db3317c6 ("signal: Better detection of synchronous signals")
Signed-off-by: Avi Weiss <thnkslprpt@gmail.com>
---

Reproduced by blocking SIGSEGV, queuing a positive-code SIGSEGV
with rt_tgsigqueueinfo(), then triggering an unblocked SIGTRAP.
Without the fix, SIGSEGV was delivered while still blocked.

Patched version behaved as expected.

 kernel/signal.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index e433de93b430..4dcc47a7d30d 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -684,12 +684,13 @@ static int dequeue_synchronous_signal(kernel_siginfo_t *info)
 		return 0;
 
 	/*
-	 * Return the first synchronous signal in the queue.
+	 * Return the first unblocked synchronous signal in the queue.
 	 */
 	list_for_each_entry(q, &pending->list, list) {
 		/* Synchronous signals have a positive si_code */
 		if ((q->info.si_code > SI_USER) &&
-		    (sigmask(q->info.si_signo) & SYNCHRONOUS_MASK)) {
+		    (sigmask(q->info.si_signo) & SYNCHRONOUS_MASK) &&
+		    !sigismember(&tsk->blocked, q->info.si_signo)) {
 			sync = q;
 			goto next;
 		}

base-commit: f47d223627f80cb7a1eb14c585fe6cb35de5e984
-- 
2.43.0