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=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham 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 32F56C433E1 for ; Fri, 21 Aug 2020 19:47:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0414C208DB for ; Fri, 21 Aug 2020 19:47:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598039237; bh=f3yVDNBJvnGh5Iokm9/PFcobvsO5ALwAD6QUltmqU44=; h=From:To:Cc:Subject:Date:In-Reply-To:References:In-Reply-To: References:List-ID:From; b=2G/z9Xstqz46glEvcvpjmNrgLzx4Tlhj9WLTIgGnK6kJMr4RFYunQDIGJGfPlieLU UepxC80MJTYeehkxdVAqtSPPsKgZixU2ZbrCkv14jQiZ/c9hScoT3iM2+oFWVFrKjw sI7nJbtGOJKfa8P1PxoRd4JpTfIcDQOZiSJYGohw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727087AbgHUTrM (ORCPT ); Fri, 21 Aug 2020 15:47:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:40876 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726431AbgHUTrH (ORCPT ); Fri, 21 Aug 2020 15:47:07 -0400 Received: from localhost.localdomain (c-73-211-240-131.hsd1.il.comcast.net [73.211.240.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 751F9207CD; Fri, 21 Aug 2020 19:47:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598039227; bh=f3yVDNBJvnGh5Iokm9/PFcobvsO5ALwAD6QUltmqU44=; h=From:To:Cc:Subject:Date:In-Reply-To:References:In-Reply-To: References:From; b=ROw4/dA9/I7gR7iBcQaILUsDT3BjeLbI0NaqMjjSuJ6Hp1tnzfH43aW232ggfONWu klj1gm3NJFLaEepo/RXDEUtf9ERdfs/InGgqpGDxRsv4bjgQUVxLSxkSsIv6oArWuh 8Zzr/3p8R7ywfPqL57iwZyHzya1i2lHYrbZRhIDE= From: zanussi@kernel.org To: LKML , linux-rt-users , Steven Rostedt , Thomas Gleixner , Carsten Emde , John Kacur , Sebastian Andrzej Siewior , Daniel Wagner , Clark Williams , Pavel Machek , Tom Zanussi Cc: Matt Fleming Subject: [PATCH RT 1/5] signal: Prevent double-free of user struct Date: Fri, 21 Aug 2020 14:47:00 -0500 Message-Id: <544fad9036a21c60dc68278fa302cc5cdf477098.1598039186.git.zanussi@kernel.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Matt Fleming v4.19.135-rt61-rc1 stable review patch. If anyone has any objections, please let me know. ----------- [ Upsteam commit 9567db2ebe566a93485e1a27d8759969d0002d7a ] 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: Tom Zanussi --- kernel/signal.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/signal.c b/kernel/signal.c index 45748993f777..05c9b5a6b3ae 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -488,8 +488,8 @@ 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); } -- 2.17.1