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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 69CECC49ED7 for ; Tue, 17 Sep 2019 00:50:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4625A20640 for ; Tue, 17 Sep 2019 00:50:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732735AbfIQAuo (ORCPT ); Mon, 16 Sep 2019 20:50:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60312 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732054AbfIQAuo (ORCPT ); Mon, 16 Sep 2019 20:50:44 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0B0893082132; Tue, 17 Sep 2019 00:50:44 +0000 (UTC) Received: from ming.t460p (ovpn-8-18.pek2.redhat.com [10.72.8.18]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 44FA35D6A9; Tue, 17 Sep 2019 00:50:36 +0000 (UTC) Date: Tue, 17 Sep 2019 08:50:32 +0800 From: Ming Lei To: Yufen Yu Cc: axboe@kernel.dk, linux-block@vger.kernel.org, hch@infradead.org, keith.busch@intel.com, tj@kernel.org, zhangxiaoxu5@huawei.com Subject: Re: [PATCH] block: fix null pointer dereference in blk_mq_rq_timed_out() Message-ID: <20190917005030.GD6199@ming.t460p> References: <20190907102450.40291-1-yuyufen@huawei.com> <20190912024618.GE2731@ming.t460p> <20190912041658.GA5020@ming.t460p> <20190912100755.GB9897@ming.t460p> <04b485ad-90e6-7752-b74f-9694de9c22a6@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <04b485ad-90e6-7752-b74f-9694de9c22a6@huawei.com> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Tue, 17 Sep 2019 00:50:44 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, Sep 16, 2019 at 05:27:39PM +0800, Yufen Yu wrote: > > > On 2019/9/12 18:07, Ming Lei wrote: > > On Thu, Sep 12, 2019 at 04:49:15PM +0800, Yufen Yu wrote: > > > > > > On 2019/9/12 12:16, Ming Lei wrote: > > > > On Thu, Sep 12, 2019 at 11:29:18AM +0800, Yufen Yu wrote: > > > > > On 2019/9/12 10:46, Ming Lei wrote: > > > > > > On Sat, Sep 07, 2019 at 06:24:50PM +0800, Yufen Yu wrote: > > > > > > > There is a race condition between timeout check and completion for > > > > > > > flush request as follow: > > > > > > > > > > > > > > timeout_work issue flush issue flush > > > > > > > blk_insert_flush > > > > > > > blk_insert_flush > > > > > > > blk_mq_timeout_work > > > > > > > blk_kick_flush > > > > > > > > > > > > > > blk_mq_queue_tag_busy_iter > > > > > > > blk_mq_check_expired(flush_rq) > > > > > > > > > > > > > > __blk_mq_end_request > > > > > > > flush_end_io > > > > > > > blk_kick_flush > > > > > > > blk_rq_init(flush_rq) > > > > > > > memset(flush_rq, 0) > > > > > > Not see there is memset(flush_rq, 0) in block/blk-flush.c > > > > > Call path as follow: > > > > > > > > > > blk_kick_flush > > > > > blk_rq_init > > > > > memset(rq, 0, sizeof(*rq)); > > > > Looks I miss this one in blk_rq_init(), sorry for that. > > > > > > > > Given there are only two users of blk_rq_init(), one simple fix could be > > > > not clearing queue in blk_rq_init(), something like below? > > > > > > > > diff --git a/block/blk-core.c b/block/blk-core.c > > > > index 77807a5d7f9e..25e6a045c821 100644 > > > > --- a/block/blk-core.c > > > > +++ b/block/blk-core.c > > > > @@ -107,7 +107,9 @@ EXPORT_SYMBOL_GPL(blk_queue_flag_test_and_set); > > > > void blk_rq_init(struct request_queue *q, struct request *rq) > > > > { > > > > - memset(rq, 0, sizeof(*rq)); > > > > + const int offset = offsetof(struct request, q); > > > > + > > > > + memset((void *)rq + offset, 0, sizeof(*rq) - offset); > > > > INIT_LIST_HEAD(&rq->queuelist); > > > > rq->q = q; > > > > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h > > > > index 1ac790178787..382e71b8787d 100644 > > > > --- a/include/linux/blkdev.h > > > > +++ b/include/linux/blkdev.h > > > > @@ -130,7 +130,7 @@ enum mq_rq_state { > > > > * especially blk_mq_rq_ctx_init() to take care of the added fields. > > > > */ > > > > struct request { > > > > - struct request_queue *q; > > > > + struct request_queue *q; /* Must be the 1st field */ > > > > struct blk_mq_ctx *mq_ctx; > > > > struct blk_mq_hw_ctx *mq_hctx; > > > Not set req->q as '0' can just avoid BUG_ON for NULL pointer deference. > > > > > > However, the root problem is that 'flush_rq' have been reused while > > > timeout function handle it currently. That means mq_ops->timeout() may > > > access old values remained by the last flush request and make the wrong > > > decision. > > > > > > Take the race condition in the patch as an example. > > > > > > blk_mq_check_expired > > > blk_mq_rq_timed_out > > > req->q->mq_ops->timeout // Driver timeout handle may read old data > > > refcount_dec_and_test(&rq) > > > __blk_mq_free_request // If rq have been reset has '1' in > > > blk_rq_init(), it will be free here. > > > > > > So, I think we should solve this problem completely. Just like normal > > > request, > > > we can prevent flush request to call end_io when timeout handle the request. > > Seems it isn't specific for 'flush_rq', and it should be one generic issue > > for any request which implements .end_io. > > > > For requests without defining .end_io, rq->ref is applied for protecting > > its lifetime. However, rq->end_io() is still called even if rq->ref doesn't > > drop to zero. > > > > If the above is correct, we need to let rq->ref to cover rq->end_io(). > > We ignore the fact that we may also need to free 'rq' after calling > rq->end_io(), > such as end_clone_request(), mq_flush_data_end_io(). > > If we let 'rq->ref' to cover rq->end_io(), 'rq->ref' have been decreased to > '0' > before calling __blk_mq_free_request(). Then, the function will never be > called. > > So, I think flush request may need to be fixed individually. Thinking of this issue further, given other cases of .end_io() still depends on blk_mq_free_request() for freeing request, it is fine to just fix flush request. Thanks, Ming