linux-kernel - [PATCH 1/3] signals: fix sigqueue_free() vs __exit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20080517151418.GA9487@tv-sign.ru>
Date:	Sat, 17 May 2008 19:14:18 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Roland McGrath <roland@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] signals: fix sigqueue_free() vs __exit_signal() race

__exit_signal() does flush_sigqueue(tsk->pending) outside of ->siglock.
This can race with another thread doing sigqueue_free(), we can free
the same SIGQUEUE_PREALLOC sigqueue twice or corrupt the pending->list.

Note that even sys_exit_group() can trigger this race, not only
sys_timer_delete().

Move the callsite of flush_sigqueue(tsk->pending) under ->siglock.

This patch doesn't touch flush_sigqueue(->shared_pending) below, it is
called when there are no other threads which can play with signals,
and sigqueue_free() can't be used outside of our thread group.

Signed-off-by: Oleg Nesterov <oleg@...sign.ru>
Acked-by: Roland McGrath <roland@...hat.com>

--- 25/kernel/exit.c~1_SQFREE_EXIT_RACE	2008-05-17 16:03:29.000000000 +0400
+++ 25/kernel/exit.c	2008-05-17 16:22:07.000000000 +0400
@@ -125,6 +125,12 @@ static void __exit_signal(struct task_st
 
 	__unhash_process(tsk);
 
+	/*
+	 * Do this under ->siglock, we can race with another thread
+	 * doing sigqueue_free() if we have SIGQUEUE_PREALLOC signals.
+	 */
+	flush_sigqueue(&tsk->pending);
+
 	tsk->signal = NULL;
 	tsk->sighand = NULL;
 	spin_unlock(&sighand->siglock);
@@ -132,7 +138,6 @@ static void __exit_signal(struct task_st
 
 	__cleanup_sighand(sighand);
 	clear_tsk_thread_flag(tsk,TIF_SIGPENDING);
-	flush_sigqueue(&tsk->pending);
 	if (sig) {
 		flush_sigqueue(&sig->shared_pending);
 		taskstats_tgid_free(sig);
--- 25/kernel/signal.c~1_SQFREE_EXIT_RACE	2008-05-17 16:03:29.000000000 +0400
+++ 25/kernel/signal.c	2008-05-17 16:22:07.000000000 +0400
@@ -1242,7 +1242,8 @@ void sigqueue_free(struct sigqueue *q)
 	/*
 	 * If the signal is still pending remove it from the
 	 * pending queue. We must hold ->siglock while testing
-	 * q->list to serialize with collect_signal().
+	 * q->list to serialize with collect_signal() or with
+	 * __exit_signal()->flush_sigqueue().
 	 */
 	spin_lock_irqsave(lock, flags);
 	if (!list_empty(&q->list))

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/