[Qemu-devel] [PATCH 11/12] qcow2/overlaps: Protect inactive L2 tables

[Max Reitz <mreitz@redhat.com>]

Keep track of the inactive L2 tables in the metadata list to protect
them against accidental modifications.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2-refcount.c | 20 ++++++++++++++++++++
 block/qcow2-snapshot.c | 41 +++++++++++++++++++++++++++++++++++++++--
 2 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 6cf73e9..0c203d3 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1045,8 +1045,28 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
                         s->cluster_bits, addend, QCOW2_DISCARD_SNAPSHOT);
                 if (addend < 0) {
                     if (l1_allocated) {
+                        /* This is easy */
                         qcow2_metadata_list_remove(bs, l2_offset, 1,
                                                    QCOW2_OL_ACTIVE_L2);
+                    } else {
+                        /* If refcount == 0, this is, too. If refcount > 1, we
+                         * know that there must be some other inactive L2
+                         * reference; and for refcount == 1, if this is an
+                         * active L2 table, this was the last inactive L2
+                         * reference. */
+                        bool remove;
+                        if (refcount == 0) {
+                            remove = true;
+                        } else if (refcount == 1) {
+                            remove = qcow2_check_metadata_overlap(bs,
+                                ~QCOW2_OL_ACTIVE_L2, l2_offset,s->cluster_size);
+                        } else {
+                            remove = false;
+                        }
+                        if (remove) {
+                            qcow2_metadata_list_remove(bs, l2_offset, 1,
+                                                       QCOW2_OL_INACTIVE_L2);
+                        }
                     }
                 }
             } else {
diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index b3122d8..800c7d3 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -46,9 +46,10 @@ int qcow2_read_snapshots(BlockDriverState *bs)
     QCowSnapshotHeader h;
     QCowSnapshotExtraData extra;
     QCowSnapshot *sn;
-    int i, id_str_size, name_size;
+    int i, j, id_str_size, name_size;
     int64_t offset;
     uint32_t extra_data_size;
+    uint64_t *l1_table;
     int ret;
 
     if (!s->nb_snapshots) {
@@ -122,7 +123,8 @@ int qcow2_read_snapshots(BlockDriverState *bs)
             goto fail;
         }
 
-        if (!(s->overlap_check & QCOW2_OL_INACTIVE_L1)) {
+        if (!(s->overlap_check & (QCOW2_OL_INACTIVE_L1 | QCOW2_OL_INACTIVE_L2)))
+        {
             continue;
         }
 
@@ -136,6 +138,34 @@ int qcow2_read_snapshots(BlockDriverState *bs)
                                   size_to_clusters(s, sn->l1_size *
                                                       sizeof(uint64_t)),
                                   QCOW2_OL_INACTIVE_L1);
+
+        if (!(s->overlap_check & QCOW2_OL_INACTIVE_L2)) {
+            continue;
+        }
+
+        l1_table = qemu_try_blockalign(bs->file,
+                                       sn->l1_size * sizeof(uint64_t));
+        if (!l1_table) {
+            /* Do not fail opening the image just because a snapshot's L2 tables
+             * cannot be covered by the overlap checks */
+            continue;
+        }
+
+        ret = bdrv_pread(bs->file, sn->l1_table_offset, l1_table,
+                         sn->l1_size * sizeof(uint64_t));
+        if (ret < 0) {
+            qemu_vfree(l1_table);
+            continue;
+        }
+        for (j = 0; j < sn->l1_size; j++) {
+            uint64_t l2_offset = be64_to_cpu(l1_table[j]) & L1E_OFFSET_MASK;
+            if (l2_offset) {
+                qcow2_metadata_list_enter(bs, l2_offset, 1,
+                                          QCOW2_OL_INACTIVE_L2);
+            }
+        }
+
+        qemu_vfree(l1_table);
     }
 
     assert(offset - s->snapshots_offset <= INT_MAX);
@@ -436,6 +466,13 @@ int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
                                                   sizeof(uint64_t)),
                               QCOW2_OL_INACTIVE_L1);
 
+    for (i = 0; i < s->l1_size; i++) {
+        uint64_t l2_offset = s->l1_table[i] & L1E_OFFSET_MASK;
+        if (l2_offset) {
+            qcow2_metadata_list_enter(bs, l2_offset, 1, QCOW2_OL_INACTIVE_L2);
+        }
+    }
+
     /*
      * Increase the refcounts of all clusters and make sure everything is
      * stable on disk before updating the snapshot table to contain a pointer
-- 
1.9.3