From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48544) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dmUCh-0001YY-Qp for qemu-devel@nongnu.org; Mon, 28 Aug 2017 20:16:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dmUCe-0005oz-5j for qemu-devel@nongnu.org; Mon, 28 Aug 2017 20:16:27 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:42402 helo=mx0a-001b2d01.pphosted.com) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dmUCd-0005nj-Vf for qemu-devel@nongnu.org; Mon, 28 Aug 2017 20:16:24 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v7T0EBJ8019642 for ; Mon, 28 Aug 2017 20:16:23 -0400 Received: from e35.co.us.ibm.com (e35.co.us.ibm.com [32.97.110.153]) by mx0b-001b2d01.pphosted.com with ESMTP id 2cmsfn2wme-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 28 Aug 2017 20:16:23 -0400 Received: from localhost by e35.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 28 Aug 2017 18:16:22 -0600 From: Michael Roth Date: Mon, 28 Aug 2017 19:14:32 -0500 In-Reply-To: <1503965694-10794-1-git-send-email-mdroth@linux.vnet.ibm.com> References: <1503965694-10794-1-git-send-email-mdroth@linux.vnet.ibm.com> Message-Id: <1503965694-10794-58-git-send-email-mdroth@linux.vnet.ibm.com> Subject: [Qemu-devel] [PATCH 57/79] commit: Fix use after free in completion List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Kevin Wolf From: Kevin Wolf The final bdrv_set_backing_hd() could be working on already freed nodes because the commit job drops its references (through BlockBackends) to both overlay_bs and top already a bit earlier. One way to trigger the bug is hot unplugging a disk for which blockdev_mark_auto_del() cancels the block job. Fix this by taking BDS-level references while we're still using the nodes. Cc: qemu-stable@nongnu.org Signed-off-by: Kevin Wolf Reviewed-by: John Snow (cherry picked from commit 19ebd13ed45ad5d5f277f5914d55b83f13eb09eb) Signed-off-by: Michael Roth --- block/commit.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/block/commit.c b/block/commit.c index 76a0d98..3bae46e 100644 --- a/block/commit.c +++ b/block/commit.c @@ -89,6 +89,10 @@ static void commit_complete(BlockJob *job, void *opaque) int ret = data->ret; bool remove_commit_top_bs = false; + /* Make sure overlay_bs and top stay around until bdrv_set_backing_hd() */ + bdrv_ref(top); + bdrv_ref(overlay_bs); + /* Remove base node parent that still uses BLK_PERM_WRITE/RESIZE before * the normal backing chain can be restored. */ blk_unref(s->base); @@ -124,6 +128,9 @@ static void commit_complete(BlockJob *job, void *opaque) if (remove_commit_top_bs) { bdrv_set_backing_hd(overlay_bs, top, &error_abort); } + + bdrv_unref(overlay_bs); + bdrv_unref(top); } static void coroutine_fn commit_run(void *opaque) -- 2.7.4