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bh=kSzzwRz99E9b98BSBSDMrjfyRmdFrqX2049eUPiwmWA=; b=RMvxcqbReSLUvTMuhwq6xSuVUlpW3LCUs4bARVzEmYrEgxrKhUB6IsaywapeEjGRWY1LWZ wc8bL4hsYzqa+ZlxF8Cn4U0okBs6mLWBhZ6QMkDvuJ/Ji3/mP1ghBNyDPtHVF8oIIgZl7M FAKPI3Pch8Pzzq+2RnIyw4dL/NuQrFs= X-MC-Unique: rOZkeXANNuOIQ2u7D-e8ww-1 From: Kevin Wolf To: qemu-block@nongnu.org Subject: [PULL 1/1] qcow2: Fix corruption on write_zeroes with MAY_UNMAP Date: Tue, 24 Nov 2020 15:24:59 +0100 Message-Id: <20201124142459.298166-2-kwolf@redhat.com> In-Reply-To: <20201124142459.298166-1-kwolf@redhat.com> References: <20201124142459.298166-1-kwolf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=216.205.24.124; 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_H3=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: kwolf@redhat.com, peter.maydell@linaro.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: pass (identity @redhat.com) Content-Type: text/plain; charset="utf-8" From: Maxim Levitsky 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 [ kwolf: Fixed to restore the correct original order from before 205fa50750; added comments like in discard_in_l2_slice(). ] Signed-off-by: Kevin Wolf Message-Id: <20201124092815.39056-1-kwolf@redhat.com> Reviewed-by: Alberto Garcia Signed-off-by: Kevin Wolf --- block/qcow2-cluster.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 485b4cb92e..bd0597842f 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -2010,14 +2010,17 @@ static int zero_in_l2_slice(BlockDriverState *bs, u= int64_t offset, continue; } =20 + /* First update L2 entries */ 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); if (has_subclusters(s)) { set_l2_bitmap(s, l2_slice, l2_index + i, new_l2_bitmap); } + + /* Then decrease the refcount */ + if (unmap) { + qcow2_free_any_cluster(bs, old_l2_entry, QCOW2_DISCARD_REQUEST= ); + } } =20 qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice); --=20 2.28.0