signal: Always ignore SIGKILL and SIGSTOP sent to the global init

[ Upstream commit 86989c4 ] If the first process started (aka /sbin/init) receives a SIGKILL it will panic the system if it is delivered. Making the system unusable and undebugable. It isn't much better if the first process started receives SIGSTOP. So always ignore SIGSTOP and SIGKILL sent to init. This is done in a separate clause in sig_task_ignored as force_sig_info can clear SIG_UNKILLABLE and this protection should work even then. Reviewed-by: Thomas Gleixner <[email protected]> Signed-off-by: "Eric W. Biederman" <[email protected]> Signed-off-by: Sasha Levin <[email protected]>
crdroidandroid · Nov 20, 2019 · 0935780 · 0935780
1 parent ee01347
commit 0935780
Showing 1 changed file with 4 additions and 0 deletions.
diff --git a/kernel/signal.c b/kernel/signal.c
@@ -77,6 +77,10 @@ static int sig_task_ignored(struct task_struct *t, int sig, bool force)
 
 	handler = sig_handler(t, sig);
 
+	/* SIGKILL and SIGSTOP may not be sent to the global init */
+	if (unlikely(is_global_init(t) && sig_kernel_only(sig)))
+		return true;
+
 	if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) &&
 	    handler == SIG_DFL && !(force && sig_kernel_only(sig)))
 		return 1;