[PATCH 5.15 050/262] signal: In get_signal test for signal_group_exit every time through the loop

[Greg Kroah-Hartman]

From: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>

[ Upstream commit e7f7c99ba911f56bc338845c1cd72954ba591707 ]

Recently while investigating a problem with rr and signals I noticed
that siglock is dropped in ptrace_signal and get_signal does not jump
to relock.

Looking farther to see if the problem is anywhere else I see that
do_signal_stop also returns if signal_group_exit is true.  I believe
that test can now never be true, but it is a bit hard to trace
through and be certain.

Testing signal_group_exit is not expensive, so move the test for
signal_group_exit into the for loop inside of get_signal to ensure
the test is never skipped improperly.

This has been a potential problem since I added the test for
signal_group_exit was added.

Fixes: 35634ffa1751 ("signal: Always notice exiting tasks")
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/875yssekcd.fsf_-_@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/signal.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index aea93d6a5520a..6e3dbb3d12170 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2710,19 +2710,19 @@ bool get_signal(struct ksignal *ksig)
 		goto relock;
 	}
 
-	/* Has this task already been marked for death? */
-	if (signal_group_exit(signal)) {
-		ksig->info.si_signo = signr = SIGKILL;
-		sigdelset(&current->pending.signal, SIGKILL);
-		trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO,
-				&sighand->action[SIGKILL - 1]);
-		recalc_sigpending();
-		goto fatal;
-	}
-
 	for (;;) {
 		struct k_sigaction *ka;
 
+		/* Has this task already been marked for death? */
+		if (signal_group_exit(signal)) {
+			ksig->info.si_signo = signr = SIGKILL;
+			sigdelset(&current->pending.signal, SIGKILL);
+			trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO,
+				&sighand->action[SIGKILL - 1]);
+			recalc_sigpending();
+			goto fatal;
+		}
+
 		if (unlikely(current->jobctl & JOBCTL_STOP_PENDING) &&
 		    do_signal_stop(0))
 			goto relock;
-- 
2.34.1