From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: [PATCH] Fix a use-after-free triggered by device removal Date: Thu, 06 Sep 2012 19:58:54 +0200 Message-ID: <5048E45E.1070302@acm.org> References: <5044BAD2.7060901@acm.org> <91D94272-CA62-4E68-87D7-CE77DE776CC9@cs.wisc.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Received: from georges.telenet-ops.be ([195.130.137.68]:54932 "EHLO georges.telenet-ops.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932609Ab2IFR65 (ORCPT ); Thu, 6 Sep 2012 13:58:57 -0400 In-Reply-To: <91D94272-CA62-4E68-87D7-CE77DE776CC9@cs.wisc.edu> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Michael Christie Cc: linux-scsi , James Bottomley , Jens Axboe , Tejun Heo , Chanho Min _suOn 09/06/12 18:27, Michael Christie wrote: > On Sep 3, 2012, at 9:12 AM, Bart Van Assche wrote: >> If the put_device() call in scsi_request_fn() drops the sdev refcount >> to zero then the spin_lock() call after the put_device() call triggers >> a use-after-free. Avoid that by making sure that blk_cleanup_queue() >> can only finish after all active scsi_request_fn() calls have returned. > > If we have this patch http://marc.info/?l=linux-scsi&m=134453905402413&w=2 > it seems we have all the scsi layer callers of the request_fn/ > *blk_run_queue holding a reference to the device when they make the call. > Right, or are there some other places missing? > > What are the other places we can call the request_fn without already > holding a reference to the device? Is it the block layer? Is that why we > need this patch? Hello Mike, The purpose of this patch is indeed to make *blk_run_queue() calls from the block layer safe. There are several direct or indirect *blk_run_queue() calls in the block layer where a reference on the queue is held but not on the sdev, e.g. in the md, dm and bsg drivers. Bart.