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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 43549C07E96 for ; Tue, 6 Jul 2021 13:44:08 +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 D18CA619D4 for ; Tue, 6 Jul 2021 13:44:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D18CA619D4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:54926 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1m0lMs-0007On-Tk for qemu-devel@archiver.kernel.org; Tue, 06 Jul 2021 09:44:06 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44006) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m0lM2-0006ae-9t for qemu-devel@nongnu.org; Tue, 06 Jul 2021 09:43:14 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:42488) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m0lLz-0003F3-AP for qemu-devel@nongnu.org; Tue, 06 Jul 2021 09:43:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1625578990; 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: in-reply-to:in-reply-to:references:references; bh=3HUnIPUu5ZAm72271XjwUtAOAl7HP+jYQNp54LkyphI=; b=VXECx+FivTspm1aYbxNRxCmTrOOkhVpb9dNFri0oArmz4abdwP8uxwQS0G8/yCwl4wBglq aD3PZ3KvniWkQ+qFBE31QQahyv1At/t/wXgyjfacusAa7djMugJW9nLLooYeHvr9Wlkv8F QoD94jVyYfvEn5ml09sY0g1CtShfjtw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-328-135aehr9PLaJt4ZJrk1vUA-1; Tue, 06 Jul 2021 09:43:07 -0400 X-MC-Unique: 135aehr9PLaJt4ZJrk1vUA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 01E641084F58; Tue, 6 Jul 2021 13:43:06 +0000 (UTC) Received: from redhat.com (ovpn-113-253.ams2.redhat.com [10.36.113.253]) by smtp.corp.redhat.com (Postfix) with ESMTPS id AF8AB60CC9; Tue, 6 Jul 2021 13:43:04 +0000 (UTC) Date: Tue, 6 Jul 2021 15:43:03 +0200 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH v5 1/6] qcow2: Fix dangling pointer after reopen for 'file' Message-ID: References: <20210706112340.223334-1-kwolf@redhat.com> <20210706112340.223334-2-kwolf@redhat.com> <9b8d2ae9-d4fe-8643-b384-5de2e8bea5ce@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <9b8d2ae9-d4fe-8643-b384-5de2e8bea5ce@virtuozzo.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.442, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: berto@igalia.com, qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 06.07.2021 um 15:12 hat Vladimir Sementsov-Ogievskiy geschrieben: > 06.07.2021 14:23, Kevin Wolf wrote: > > Without an external data file, s->data_file is a second pointer with the > > same value as bs->file. When changing bs->file to a different BdrvChild > > and freeing the old BdrvChild, s->data_file must also be updated, > > otherwise it points to freed memory and causes crashes. > > > > This problem was caught by iotests case 245. > > > > Fixes: df2b7086f169239ebad5d150efa29c9bb6d4f820 > > Signed-off-by: Kevin Wolf > > Reviewed-by: Vladimir Sementsov-Ogievskiy > > Still, some ideas below: > > > --- > > block/qcow2.c | 14 ++++++++++++++ > > 1 file changed, 14 insertions(+) > > > > diff --git a/block/qcow2.c b/block/qcow2.c > > index ee4530cdbd..cb459ef6a6 100644 > > --- a/block/qcow2.c > > +++ b/block/qcow2.c > > @@ -962,6 +962,7 @@ static bool read_cache_sizes(BlockDriverState *bs, QemuOpts *opts, > > } > > typedef struct Qcow2ReopenState { > > + bool had_data_file; > > Qcow2Cache *l2_table_cache; > > Qcow2Cache *refcount_block_cache; > > int l2_slice_size; /* Number of entries in a slice of the L2 table */ > > @@ -1932,6 +1933,8 @@ static int qcow2_reopen_prepare(BDRVReopenState *state, > > r = g_new0(Qcow2ReopenState, 1); > > state->opaque = r; > > + r->had_data_file = has_data_file(state->bs); > > + > > So, during reopen, at some moment s->data_file become invalid. So, we > shouldn't rely on it.. > > Maybe we need > > s->data_file = NULL; > > here.. "need" is a strong word, but I guess we shouldn't access it between prepare and commit, so I agree setting it to NULL would make bugs in this area very visible. In fact, we wouldn't even need r->had_data_file then because commit could just set s->data_file = state->bs->file if it's NULL. > > ret = qcow2_update_options_prepare(state->bs, r, state->options, > > state->flags, errp); > > if (ret < 0) { > > @@ -1966,7 +1969,18 @@ fail: > > static void qcow2_reopen_commit(BDRVReopenState *state) > > { > > + BDRVQcow2State *s = state->bs->opaque; > > + Qcow2ReopenState *r = state->opaque; > > + > > qcow2_update_options_commit(state->bs, state->opaque); > > Worth doing > > assert(r->had_data_file == has_data_file(state->bs)); > > here, to be double sure? This would be wrong because at the time that this runs, state->bs->file is already updated and this is what has_data_file() checks against. So you can't use has_data_file() any more until it's synced again with the code below. In fact, this is why I even added r->had_data_file. At first I directly used has_data_file(state->bs) here and watched it break. > > + if (!r->had_data_file && s->data_file != state->bs->file) { > > + /* > > + * If s->data_file is just a second pointer to bs->file (which is the > > + * case without an external data file), it may need to be updated. > > + */ > > + s->data_file = state->bs->file; > > + assert(!has_data_file(state->bs)); > > + } > > g_free(state->opaque); > > } Kevin