From patchwork Wed Mar 4 10:58:19 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Cengiz Can X-Patchwork-Id: 11419881 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id A62AC1580 for ; Wed, 4 Mar 2020 10:59:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 86889217F4 for ; Wed, 4 Mar 2020 10:59:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387801AbgCDK7J (ORCPT ); Wed, 4 Mar 2020 05:59:09 -0500 Received: from relay3-d.mail.gandi.net ([217.70.183.195]:55391 "EHLO relay3-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387805AbgCDK7I (ORCPT ); Wed, 4 Mar 2020 05:59:08 -0500 X-Originating-IP: 176.88.145.204 Received: from localhost.localdomain (unknown [176.88.145.204]) (Authenticated sender: cengiz@kernel.wtf) by relay3-d.mail.gandi.net (Postfix) with ESMTPSA id 9B91560009; Wed, 4 Mar 2020 10:59:03 +0000 (UTC) From: Cengiz Can To: Jens Axboe , Steven Rostedt , Ingo Molnar Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Cengiz Can Subject: [PATCH v2] blktrace: fix dereference after null check Date: Wed, 4 Mar 2020 13:58:19 +0300 Message-Id: <20200304105818.11781-1-cengiz@kernel.wtf> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org There was a recent change in blktrace.c that added a RCU protection to `q->blk_trace` in order to fix a use-after-free issue during access. However the change missed an edge case that can lead to dereferencing of `bt` pointer even when it's NULL: Coverity static analyzer marked this as a FORWARD_NULL issue with CID 1460458. ``` /kernel/trace/blktrace.c: 1904 in sysfs_blk_trace_attr_store() 1898 ret = 0; 1899 if (bt == NULL) 1900 ret = blk_trace_setup_queue(q, bdev); 1901 1902 if (ret == 0) { 1903 if (attr == &dev_attr_act_mask) >>> CID 1460458: Null pointer dereferences (FORWARD_NULL) >>> Dereferencing null pointer "bt". 1904 bt->act_mask = value; 1905 else if (attr == &dev_attr_pid) 1906 bt->pid = value; 1907 else if (attr == &dev_attr_start_lba) 1908 bt->start_lba = value; 1909 else if (attr == &dev_attr_end_lba) ``` Added a reassignment with RCU annotation to fix the issue. Fixes: c780e86dd48 ("blktrace: Protect q->blk_trace with RCU") Signed-off-by: Cengiz Can Reviewed-by: Ming Lei Reviewed-by: Bob Liu Reviewed-by: Steven Rostedt (VMware) --- Patch Changelog * v2: Added RCU annotation to assignment kernel/trace/blktrace.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) -- 2.25.1 diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c index 4560878f0bac..ca39dc3230cb 100644 --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -1896,8 +1896,11 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev, } ret = 0; - if (bt == NULL) + if (bt == NULL) { ret = blk_trace_setup_queue(q, bdev); + bt = rcu_dereference_protected(q->blk_trace, + lockdep_is_held(&q->blk_trace_mutex)); + } if (ret == 0) { if (attr == &dev_attr_act_mask)