From patchwork Fri Sep 7 16:15:15 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kevin Wolf X-Patchwork-Id: 10592331 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 9B16113BB for ; Fri, 7 Sep 2018 16:18:38 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8F0D92B7E6 for ; Fri, 7 Sep 2018 16:18:38 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 836122B7F8; Fri, 7 Sep 2018 16:18:38 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 1A9C42B7E6 for ; Fri, 7 Sep 2018 16:18:38 +0000 (UTC) Received: from localhost ([::1]:39455 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fyJSv-00008E-AF for patchwork-qemu-devel@patchwork.kernel.org; Fri, 07 Sep 2018 12:18:37 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53464) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fyJQg-0006Lz-Qk for qemu-devel@nongnu.org; Fri, 07 Sep 2018 12:16:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fyJQa-0004M8-RC for qemu-devel@nongnu.org; Fri, 07 Sep 2018 12:16:16 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:58564 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fyJQS-0003op-2I; Fri, 07 Sep 2018 12:16:04 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9825B8010FDF; Fri, 7 Sep 2018 16:15:57 +0000 (UTC) Received: from localhost.localdomain.com (ovpn-116-56.ams2.redhat.com [10.36.116.56]) by smtp.corp.redhat.com (Postfix) with ESMTP id 48FD12157F45; Fri, 7 Sep 2018 16:15:56 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Date: Fri, 7 Sep 2018 18:15:15 +0200 Message-Id: <20180907161520.26349-10-kwolf@redhat.com> In-Reply-To: <20180907161520.26349-1-kwolf@redhat.com> References: <20180907161520.26349-1-kwolf@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Fri, 07 Sep 2018 16:15:57 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Fri, 07 Sep 2018 16:15:57 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'kwolf@redhat.com' RCPT:'' X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 66.187.233.73 Subject: [Qemu-devel] [PATCH 09/14] block-backend: Fix potential double blk_delete() X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, famz@redhat.com, slp@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com, pbonzini@redhat.com Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP blk_unref() first decreases the refcount of the BlockBackend and calls blk_delete() if the refcount reaches zero. Requests can still be in flight at this point, they are only drained during blk_delete(): At this point, arbitrary callbacks can run. If any callback takes a temporary BlockBackend reference, it will first increase the refcount to 1 and then decrease it to 0 again, triggering another blk_delete(). This will cause a use-after-free crash in the outer blk_delete(). Fix it by draining the BlockBackend before decreasing to refcount to 0. Assert in blk_ref() that it never takes the first refcount (which would mean that the BlockBackend is already being deleted). Signed-off-by: Kevin Wolf Reviewed-by: Fam Zheng --- block/block-backend.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/block/block-backend.c b/block/block-backend.c index efa8d8011c..1b2d7a6ff5 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -435,6 +435,7 @@ int blk_get_refcnt(BlockBackend *blk) */ void blk_ref(BlockBackend *blk) { + assert(blk->refcnt > 0); blk->refcnt++; } @@ -447,7 +448,11 @@ void blk_unref(BlockBackend *blk) { if (blk) { assert(blk->refcnt > 0); - if (!--blk->refcnt) { + if (blk->refcnt > 1) { + blk->refcnt--; + } else { + blk_drain(blk); + blk->refcnt = 0; blk_delete(blk); } }