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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 7CE15C2BA19 for ; Wed, 15 Apr 2020 16:46:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 554622076A for ; Wed, 15 Apr 2020 16:46:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1416216AbgDOQqd (ORCPT ); Wed, 15 Apr 2020 12:46:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60290 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1416207AbgDOQqb (ORCPT ); Wed, 15 Apr 2020 12:46:31 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C6DF7C061A0C for ; Wed, 15 Apr 2020 09:46:30 -0700 (PDT) Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1jOlBE-0006ny-Gl; Wed, 15 Apr 2020 18:46:28 +0200 Date: Wed, 15 Apr 2020 18:46:28 +0200 From: Sebastian Andrzej Siewior To: Matt Fleming Cc: linux-rt@vger.kernel.org, linux-kernel@vger.kernel.org, Daniel Wagner Subject: Re: [PATCH RT] signal: Prevent double-free of user struct Message-ID: <20200415164628.2dgrj4ghvtev45sy@linutronix.de> References: <20200407095413.30039-1-matt@codeblueprint.co.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200407095413.30039-1-matt@codeblueprint.co.uk> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-04-07 10:54:13 [+0100], Matt Fleming wrote: > 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 > ? schedule_hrtimeout_range_clock+0x104/0x110 > __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 While all this sounds reasonable, may I ask what did you do to trigger this? This is v5.6 only, correct? Sebastian