linux-kernel - [PATCH v2 4/6] signal: In signal_group_exit remove the group_exit

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Date:   Tue, 23 Jun 2020 16:55:20 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     <linux-kernel@...r.kernel.org>
Cc:     <linux-fsdevel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Bernd Edlinger <bernd.edlinger@...mail.de>
Subject: [PATCH v2 4/6] signal: In signal_group_exit remove the group_exit_task test

There are two places where signal_group_exit are set.  In the
fs/exec.c:de_thread() and in fs/coredump.c:zap_threads().

The coredump usage of group_exit_task was explicitly added[1]
so that signal_group_exit() would return true during a
coredump.

When examining the coredump usage it turns out that SIGNAL_GROUP_COREDUMP
is set in all of the same places as group_exit_task.  So signal_group_exit
can test SIGNAL_GROUP_COREDUMP and achieve the same results with
respect to coredumps as testing group_exit_task.

Similarly the exec code sets and clears SIGNAL_GROUP_DETHREAD in all
of the places where group_exit_task is set and cleared.

So test SIGNAL_GROUP_COREDUMP | SIGNAL_GROUP_DETHREAD instead of
group_exit_task.

Cc: Oleg Nesterov <oleg@...hat.com>
[1] 6cd8f0acae34 ("coredump: ensure that SIGKILL always kills the dumping thread")
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 include/linux/sched/signal.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 5ff8697b21cd..43822e2b63e6 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -268,8 +268,9 @@ static inline void signal_set_stop_flags(struct signal_struct *sig,
 /* If true, all threads except ->group_exit_task have pending SIGKILL */
 static inline int signal_group_exit(const struct signal_struct *sig)
 {
-	return	(sig->flags & SIGNAL_GROUP_EXIT) ||
-		(sig->group_exit_task != NULL);
+	return	(sig->flags & (SIGNAL_GROUP_EXIT |
+			       SIGNAL_GROUP_COREDUMP |
+			       SIGNAL_GROUP_DETHREAD));
 }

 extern void flush_signals(struct task_struct *);
-- 
2.20.1