From patchwork Mon Nov 23 15:49:29 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Maxim Levitsky X-Patchwork-Id: 1404900 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: ozlabs.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=M2Myrqgk; dkim-atps=neutral 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 ozlabs.org (Postfix) with ESMTPS id 4Cfs7P3Vdmz9sRK for ; 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auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mlevitsk@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=216.205.24.124; envelope-from=mlevitsk@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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: Kevin Wolf , vsementsov@virtuozzo.com, Alberto Garcia , qemu-block@nongnu.org, zhang_youjia@126.com, Max Reitz , andrey.shinkevich@virtuozzo.com, Maxim Levitsky Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" Commit 205fa50750 ("qcow2: Add subcluster support to zero_in_l2_slice()") introduced a subtle change to code in zero_in_l2_slice: It swapped the order of 1. qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice); 2. set_l2_entry(s, l2_slice, l2_index + i, QCOW_OFLAG_ZERO); 3. qcow2_free_any_clusters(bs, old_offset, 1, QCOW2_DISCARD_REQUEST); To 1. qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice); 2. qcow2_free_any_clusters(bs, old_offset, 1, QCOW2_DISCARD_REQUEST); 3. set_l2_entry(s, l2_slice, l2_index + i, QCOW_OFLAG_ZERO); It seems harmless, however the call to qcow2_free_any_clusters can trigger a cache flush which can mark the L2 table as clean, and assuming that this was the last write to it, a stale version of it will remain on the disk. Now we have a valid L2 entry pointing to a freed cluster. Oops. Fixes: 205fa50750 ("qcow2: Add subcluster support to zero_in_l2_slice()") Signed-off-by: Maxim Levitsky --- block/qcow2-cluster.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 485b4cb92e..267b46a4ca 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -2010,11 +2010,11 @@ static int zero_in_l2_slice(BlockDriverState *bs, uint64_t offset, continue; } - qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice); if (unmap) { qcow2_free_any_cluster(bs, old_l2_entry, QCOW2_DISCARD_REQUEST); } set_l2_entry(s, l2_slice, l2_index + i, new_l2_entry); + qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice); if (has_subclusters(s)) { set_l2_bitmap(s, l2_slice, l2_index + i, new_l2_bitmap); }