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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id CD2B5C54EBD for ; Fri, 13 Jan 2023 10:46:33 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pGHZ8-0007K2-Pa; Fri, 13 Jan 2023 05:45:42 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pGHZ5-0007Iw-7z for qemu-devel@nongnu.org; Fri, 13 Jan 2023 05:45:40 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pGHZ2-0001Kz-Kt for qemu-devel@nongnu.org; Fri, 13 Jan 2023 05:45:37 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1673606735; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=QqnfHqBiC7xiFrG3j5JTQoch6P9nMQEhItT+ElF0Ipc=; b=Qfok3b+k+LWWdwDnyUcBEdPT+NCB79fXUesggMJnUw32oqJCyL1ODad62G3aIYoT+ORb48 Nd1x5UP/Z5GESUhzye3+5EKl4kwBXpieQ6JL99PnIc0YQlxV9AoNLLD+/PiUTTI/1fJsc+ 8sgmZc0SiLcpW0hSofn48YR8KpaJDsU= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-554-0mkawJ84PJOj__gVVw8qIw-1; Fri, 13 Jan 2023 05:45:34 -0500 X-MC-Unique: 0mkawJ84PJOj__gVVw8qIw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id ECF8B3815EE6; Fri, 13 Jan 2023 10:45:33 +0000 (UTC) Received: from redhat.com (unknown [10.39.195.6]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D913B2026D76; Fri, 13 Jan 2023 10:45:32 +0000 (UTC) Date: Fri, 13 Jan 2023 11:45:31 +0100 From: Kevin Wolf To: Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Cc: qemu-block@nongnu.org, hreitz@redhat.com, aesteve@redhat.com, nsoffer@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH 1/4] qcow2: Fix theoretical corruption in store_bitmap() error path Message-ID: References: <20230112191454.169353-1-kwolf@redhat.com> <20230112191454.169353-2-kwolf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 13.01.2023 um 08:30 hat Philippe Mathieu-Daudé geschrieben: > On 12/1/23 20:14, Kevin Wolf wrote: > > In order to write the bitmap table to the image file, it is converted to > > big endian. If the write fails, it is passed to clear_bitmap_table() to > > free all of the clusters it had allocated before. However, if we don't > > convert it back to native endianness first, we'll free things at a wrong > > offset. > > > > In practical terms, the offsets will be so high that we won't actually > > free any allocated clusters, but just run into an error, but in theory > > this can cause image corruption. > > > > Cc: qemu-stable@nongnu.org > > Signed-off-by: Kevin Wolf > > --- > > block/qcow2-bitmap.c | 5 +++-- > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c > > index bcad567c0c..3dff99ba06 100644 > > --- a/block/qcow2-bitmap.c > > +++ b/block/qcow2-bitmap.c > > @@ -115,7 +115,7 @@ static int update_header_sync(BlockDriverState *bs) > > return bdrv_flush(bs->file->bs); > > } > > Maybe add a comment here remembering to bswap back to native endianness? > > > -static inline void bitmap_table_to_be(uint64_t *bitmap_table, size_t size) > > +static inline void bitmap_table_bswap_be(uint64_t *bitmap_table, size_t size) > > { > > This function uses cpu_to_be64(), semantically we convert back calling > be64_to_cpu(), but technically both functions end up being the same. Yes, but we don't seem to have any public "neutral" functions, it's always either from or to. > Alternatively: > > for (i = 0; i < size; ++i) { > - bitmap_table[i] = cpu_to_be64(bitmap_table[i]); > + bswap64s(&bitmap_table[i]); > } Doesn't that swap even on big endian hosts, resulting incorrectly in a little endian table? The closest thing we have that I can see is the be_bswap() macro in bswap.h, but it's undefined again at the end of the header. > > @@ -1401,9 +1401,10 @@ static int store_bitmap(BlockDriverState *bs, Qcow2Bitmap *bm, Error **errp) > > goto fail; > > } > > - bitmap_table_to_be(tb, tb_size); > > + bitmap_table_bswap_be(tb, tb_size); > > ret = bdrv_pwrite(bs->file, tb_offset, tb_size * sizeof(tb[0]), tb, 0); > > if (ret < 0) { > > + bitmap_table_bswap_be(tb, tb_size); > > error_setg_errno(errp, -ret, "Failed to write bitmap '%s' to file", > > bm_name); > > goto fail; > > Pre-existing, but consider using g_autofree for 'tb'. > > Reviewed-by: Philippe Mathieu-Daudé Thanks! Kevin