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=-9.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 380F3C33CAC for ; Thu, 6 Feb 2020 16:43:59 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0D31720720 for ; Thu, 6 Feb 2020 16:43:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0D31720720 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=virtuozzo.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:42238 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1izkFy-0002Fd-7N for qemu-devel@archiver.kernel.org; Thu, 06 Feb 2020 11:43:58 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:54038) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1izkF7-0001Vj-L3 for qemu-devel@nongnu.org; Thu, 06 Feb 2020 11:43:06 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1izkF6-0002Vr-DW for qemu-devel@nongnu.org; Thu, 06 Feb 2020 11:43:05 -0500 Received: from relay.sw.ru ([185.231.240.75]:49378) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1izkF3-0002JN-Gi; Thu, 06 Feb 2020 11:43:01 -0500 Received: from vovaso.qa.sw.ru ([10.94.3.0] helo=kvm.qa.sw.ru) by relay.sw.ru with esmtp (Exim 4.92.3) (envelope-from ) id 1izkEr-00007c-HR; Thu, 06 Feb 2020 19:42:49 +0300 From: Vladimir Sementsov-Ogievskiy To: qemu-block@nongnu.org Subject: [PATCH] block: fix crash on zero-length unaligned write and read Date: Thu, 6 Feb 2020 19:42:45 +0300 Message-Id: <20200206164245.17781-1-vsementsov@virtuozzo.com> X-Mailer: git-send-email 2.21.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [fuzzy] X-Received-From: 185.231.240.75 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, fam@euphon.net, vsementsov@virtuozzo.com, qemu-stable@nongnu.org, qemu-devel@nongnu.org, mreitz@redhat.com, stefanha@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Commit 7a3f542fbd "block/io: refactor padding" occasionally dropped aligning for zero-length request: bdrv_init_padding() blindly return false if bytes == 0, like there is nothing to align. This leads the following command to crash: ./qemu-io --image-opts -c 'write 1 0' \ driver=blkdebug,align=512,image.driver=null-co,image.size=512 >> qemu-io: block/io.c:1955: bdrv_aligned_pwritev: Assertion `(offset & (align - 1)) == 0' failed. >> Aborted (core dumped) Prior to 7a3f542fbd we does aligning of such zero requests. Instead of recovering this behavior let's just do nothing on such requests as it is useless. Note that driver may have special meaning of zero-length reqeusts, like qcow2_co_pwritev_compressed_part, so we can't skip any zero-length operation. But for unaligned ones, we can't pass it to driver anyway. This commit also fixes crash in iotest 80 running with -nocache: ./check -nocache -qcow2 80 which crashes on same assertion due to trying to read empty extra data in qcow2_do_read_snapshots(). Cc: qemu-stable@nongnu.org # v4.2 Fixes: 7a3f542fbd Signed-off-by: Vladimir Sementsov-Ogievskiy --- block/io.c | 28 +++++++++++++++++++++++++++- 1 file changed, 27 insertions(+), 1 deletion(-) diff --git a/block/io.c b/block/io.c index 1eb2b2bddc..7e4cb74cf4 100644 --- a/block/io.c +++ b/block/io.c @@ -1565,10 +1565,12 @@ static bool bdrv_init_padding(BlockDriverState *bs, pad->tail = align - pad->tail; } - if ((!pad->head && !pad->tail) || !bytes) { + if (!pad->head && !pad->tail) { return false; } + assert(bytes); /* Nothing good in aligning zero-length requests */ + sum = pad->head + bytes + pad->tail; pad->buf_len = (sum > align && pad->head && pad->tail) ? 2 * align : align; pad->buf = qemu_blockalign(bs, pad->buf_len); @@ -1706,6 +1708,18 @@ int coroutine_fn bdrv_co_preadv_part(BdrvChild *child, return ret; } + if (bytes == 0 && !QEMU_IS_ALIGNED(offset, bs->bl.request_alignment)) { + /* + * Aligning zero request is nonsense. Even if driver has special meaning + * of zero-length (like qcow2_co_pwritev_compressed_part), we can't pass + * it to driver due to request_alignment. + * + * Still, no reason to return an error if someone do unaligned + * zero-length read occasionally. + */ + return 0; + } + bdrv_inc_in_flight(bs); /* Don't do copy-on-read if we read data before write operation */ @@ -2116,6 +2130,18 @@ int coroutine_fn bdrv_co_pwritev_part(BdrvChild *child, return -ENOTSUP; } + if (bytes == 0 && !QEMU_IS_ALIGNED(offset, bs->bl.request_alignment)) { + /* + * Aligning zero request is nonsense. Even if driver has special meaning + * of zero-length (like qcow2_co_pwritev_compressed_part), we can't pass + * it to driver due to request_alignment. + * + * Still, no reason to return an error if someone do unaligned + * zero-length write occasionally. + */ + return 0; + } + bdrv_inc_in_flight(bs); /* * Align write if necessary by performing a read-modify-write cycle. -- 2.21.0