From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0DF9CC433E1 for ; Thu, 13 Aug 2020 01:46:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DCFB92184D for ; Thu, 13 Aug 2020 01:46:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726723AbgHMBqV (ORCPT ); Wed, 12 Aug 2020 21:46:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:33046 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726078AbgHMBp5 (ORCPT ); Wed, 12 Aug 2020 21:45:57 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 75C4F20756; Thu, 13 Aug 2020 01:45:56 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.94) (envelope-from ) id 1k62JX-0074zW-Go; Wed, 12 Aug 2020 21:45:55 -0400 Message-ID: <20200813014555.384329363@goodmis.org> User-Agent: quilt/0.66 Date: Wed, 12 Aug 2020 21:45:35 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org, linux-rt-users Cc: Thomas Gleixner , Carsten Emde , Sebastian Andrzej Siewior , John Kacur , Daniel Wagner , Tom Zanussi , "Srivatsa S. Bhat" , Matt Fleming Subject: [PATCH RT 1/6] signal: Prevent double-free of user struct References: <20200813014534.833107526@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org 5.4.54-rt33-rc1 stable review patch. If anyone has any objections, please let me know. ------------------ From: Matt Fleming The way user struct reference counting works changed significantly with, fda31c50292a ("signal: avoid double atomic counter increments for user accounting") Now user structs are only freed once the last pending signal is dequeued. Make sigqueue_free_current() follow this new convention to avoid freeing the user struct multiple times and triggering this warning: refcount_t: underflow; use-after-free. WARNING: CPU: 0 PID: 6794 at lib/refcount.c:288 refcount_dec_not_one+0x45/0x50 Call Trace: refcount_dec_and_lock_irqsave+0x16/0x60 free_uid+0x31/0xa0 __dequeue_signal+0x17c/0x190 dequeue_signal+0x5a/0x1b0 do_sigtimedwait+0x208/0x250 __x64_sys_rt_sigtimedwait+0x6f/0xd0 do_syscall_64+0x72/0x200 entry_SYSCALL_64_after_hwframe+0x49/0xbe Signed-off-by: Matt Fleming Reported-by: Daniel Wagner Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Steven Rostedt (VMware) --- kernel/signal.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/signal.c b/kernel/signal.c index def2e8e37f1f..aa924f0141cf 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -494,8 +494,8 @@ static void sigqueue_free_current(struct sigqueue *q) up = q->user; if (rt_prio(current->normal_prio) && !put_task_cache(current, q)) { - atomic_dec(&up->sigpending); - free_uid(up); + if (atomic_dec_and_test(&up->sigpending)) + free_uid(up); } else __sigqueue_free(q); } -- 2.28.0