complete_signal: kill always-true "core_state || !SIGNAL_GROUP_EXIT" check

The "(signal->core_state || !(signal->flags & SIGNAL_GROUP_EXIT))" check
in complete_signal() is not obvious at all, and in fact it only adds
unnecessary confusion: this condition is always true.

prepare_signal() does:

	if (signal->flags & SIGNAL_GROUP_EXIT) {
		if (signal->core_state)
			return sig == SIGKILL;
		/*
		 * The process is in the middle of dying, drop the signal.
		 */
		return false;
	}

This means that "!signal->core_state && (signal->flags &
SIGNAL_GROUP_EXIT)" in complete_signal() is never possible.

If SIGNAL_GROUP_EXIT is set, prepare_signal() can only return true if
signal->core_state is not NULL.

Link: https://lkml.kernel.org/r/aZsfkDhnqJ4s1oTs@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc; Deepanshu Kartikey <kartikey406@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/signal.c b/kernel/signal.c
index ca23059a947dcede67b20b6e0cee6b25d2768b46..86aad7badb9a599c3408962bbbbdd26214509163 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1000,9 +1000,7 @@ static void complete_signal(int sig, struct task_struct *p, enum pid_type type)
         * Found a killable thread.  If the signal will be fatal,
         * then start taking the whole group down immediately.
         */
-       if (sig_fatal(p, sig) &&
-           (signal->core_state || !(signal->flags & SIGNAL_GROUP_EXIT)) &&
-           !sigismember(&t->real_blocked, sig) &&
+       if (sig_fatal(p, sig) && !sigismember(&t->real_blocked, sig) &&
            (sig == SIGKILL || !p->ptrace)) {
                /*
                 * This signal will be fatal to the whole group.