signal: Restore the stop PTRACE_EVENT_EXIT

ebiederm · ebiederm · commit cf43a757fd49 · 2019-02-13T08:31:41.000-06:00
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: 35634ff ("signal: Always notice exiting tasks") Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/kernel/signal.c b/kernel/signal.c
@@ -2436,9 +2436,12 @@ bool get_signal(struct ksignal *ksig)
 	}
 
 	/* 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;
