From patchwork Tue Mar 3 07:33:59 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Cengiz Can X-Patchwork-Id: 11417327 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 49D48924 for ; Tue, 3 Mar 2020 07:37:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 24C2F20842 for ; Tue, 3 Mar 2020 07:37:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725765AbgCCHhE (ORCPT ); Tue, 3 Mar 2020 02:37:04 -0500 Received: from relay9-d.mail.gandi.net ([217.70.183.199]:40497 "EHLO relay9-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725440AbgCCHhE (ORCPT ); Tue, 3 Mar 2020 02:37:04 -0500 X-Originating-IP: 84.44.14.226 Received: from nexussix.ar.arcelik (unknown [84.44.14.226]) (Authenticated sender: cengiz@kernel.wtf) by relay9-d.mail.gandi.net (Postfix) with ESMTPSA id 99C28FF805; Tue, 3 Mar 2020 07:37:00 +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] blktrace: fix dereference after null check Date: Tue, 3 Mar 2020 10:33:59 +0300 Message-Id: <20200303073358.57799-1-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: ``` bt->act_mask = value; // bt can still be NULL here ``` Added a reassignment into the NULL check block to fix the issue. Fixes: c780e86dd48 ("blktrace: Protect q->blk_trace with RCU") Signed-off-by: Cengiz Can Reviewed-by: Bob Liu --- Huge thanks goes to Steven Rostedt for his assistance. kernel/trace/blktrace.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) -- 2.25.1 diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c index 4560878f0bac..29ea88f10b87 100644 --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -1896,8 +1896,10 @@ 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 = q->blk_trace; + } if (ret == 0) { if (attr == &dev_attr_act_mask)