signal: don't remove SIGNAL_UNKILLABLE for traced tasks.

When forcing a signal, SIGNAL_UNKILLABLE is removed to prevent recursive faults, but this is undesirable when tracing. For example, debugging an init process (whether global or namespace), hitting a breakpoint and SIGTRAP will force SIGTRAP and then remove SIGNAL_UNKILLABLE. Everything continues fine, but then once debugging has finished, the init process is left killable which is unlikely what the user expects, resulting in either an accidentally killed init or an init that stops reaping zombies. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Jamie Iles <[email protected]> Acked-by: Oleg Nesterov <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
kyagi · Aug 18, 2017 · eb61b59 · eb61b59
1 parent 6b31d59
commit eb61b59
Showing 1 changed file with 5 additions and 1 deletion.
diff --git a/kernel/signal.c b/kernel/signal.c
@@ -1194,7 +1194,11 @@ force_sig_info(int sig, struct siginfo *info, struct task_struct *t)
 			recalc_sigpending_and_wake(t);
 		}
 	}
-	if (action->sa.sa_handler == SIG_DFL)
+	/*
+	 * Don't clear SIGNAL_UNKILLABLE for traced tasks, users won't expect
+	 * debugging to leave init killable.
+	 */
+	if (action->sa.sa_handler == SIG_DFL && !t->ptrace)
 		t->signal->flags &= ~SIGNAL_UNKILLABLE;
 	ret = specific_send_sig_info(sig, info, t);
 	spin_unlock_irqrestore(&t->sighand->siglock, flags);