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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 AF443C433E0 for ; Mon, 18 May 2020 18:31:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8E70A20657 for ; Mon, 18 May 2020 18:31:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589826719; bh=bqL8njQcBWcAVj8w3cU6kdLpwiCsrDRbVhJNWo/25T8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=dG1zXzlaxkVHQ4vnwf7HSpqaAJLH3Y9S5ty22kLG+fXJC3Mbe5BFvpj7aAQrp0i9n g8z+sEYRdQ5YZG4oRhGcAxUkH/gw1EYx95JCPY47AtNf7bhGfLIq68toTKnvKPa8f5 AbMyTuRaLzfSfPTtqKvnTDdKbgeVVk+cmtZ2kluk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728760AbgERSb7 (ORCPT ); Mon, 18 May 2020 14:31:59 -0400 Received: from mail.kernel.org ([198.145.29.99]:33622 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728703AbgERRjK (ORCPT ); Mon, 18 May 2020 13:39:10 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 29E1C20829; Mon, 18 May 2020 17:39:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589823548; bh=bqL8njQcBWcAVj8w3cU6kdLpwiCsrDRbVhJNWo/25T8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1G3XIITz1a2uxmuvGdco+Iqio23WUS0MfrflPj0stHCFSGYXzPo7f+Srnw7hTLjPK F3T+sVW+zBJ9gPLMQeZHecVPcBcs8IDvS+0G5WnCxACNZJRVmd1/jf+93eSzLK13p5 DmDOu7U2MKfOI88raN8ffaxeOAMI/oG5yDoiPJqg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ming Lei , Bob Liu , "Steven Rostedt (VMware)" , Cengiz Can , Jens Axboe , Ben Hutchings Subject: [PATCH 4.4 27/86] blktrace: fix dereference after null check Date: Mon, 18 May 2020 19:35:58 +0200 Message-Id: <20200518173455.995560766@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200518173450.254571947@linuxfoundation.org> References: <20200518173450.254571947@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Cengiz Can commit 153031a301bb07194e9c37466cfce8eacb977621 upstream. 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") Reviewed-by: Ming Lei Reviewed-by: Bob Liu Reviewed-by: Steven Rostedt (VMware) Signed-off-by: Cengiz Can Signed-off-by: Jens Axboe Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- kernel/trace/blktrace.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -1822,8 +1822,11 @@ static ssize_t sysfs_blk_trace_attr_stor } 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)