signal: Restore the stop PTRACE_EVENT_EXIT

BugLink: https://bugs.launchpad.net/bugs/1837813
commit cf43a757fd49442bc38f76088b70c2299eed2c2f upstream.

In the middle of do_exit() there is there is a call
"ptrace_event(PTRACE_EVENT_EXIT, code);" That call places the process
in TACKED_TRACED aka "(TASK_WAKEKILL | __TASK_TRACED)" and waits for
for the debugger to release the task or SIGKILL to be delivered.

Skipping past dequeue_signal when we know a fatal signal has already
been delivered resulted in SIGKILL remaining pending and
TIF_SIGPENDING remaining set.  This in turn caused the
scheduler to not sleep in PTACE_EVENT_EXIT as it figured
a fatal signal was pending.  This also caused ptrace_freeze_traced
in ptrace_check_attach to fail because it left a per thread
SIGKILL pending which is what fatal_signal_pending tests for.

This difference in signal state caused strace to report
strace: Exit of unknown pid NNNNN ignored

Therefore update the signal handling state like dequeue_signal
would when removing a per thread SIGKILL, by removing SIGKILL
from the per thread signal mask and clearing TIF_SIGPENDING.

Acked-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Ivan Delalande <colona@arista.com>
Cc: stable@vger.kernel.org
Fixes: 35634ffa1751 ("signal: Always notice exiting tasks")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/kernel/signal.c b/kernel/signal.c
index 70b936c064ba3538d26ff5c0a705bcbd79755ea8..eab385c966fa5cd016db0475ded55ec058cc07a8 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2268,9 +2268,12 @@ relock:
        }
 
        /* Has this task already been marked for death? */
-       ksig->info.si_signo = signr = SIGKILL;
-       if (signal_group_exit(signal))
+       if (signal_group_exit(signal)) {
+               ksig->info.si_signo = signr = SIGKILL;
+               sigdelset(&current->pending.signal, SIGKILL);
+               recalc_sigpending();
                goto fatal;
+       }
 
        for (;;) {
                struct k_sigaction *ka;