qcow2: Check L1/L2/reftable entries for alignment

Offsets taken from the L1, L2 and refcount tables are generally assumed
to be correctly aligned. However, this cannot be guaranteed if the image
has been written to by something different than qemu, thus check all
offsets taken from these tables for correct cluster alignment.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1409926039-29044-5-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 40 insertions, 3 deletions

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 735f687b06..f7dd8c0985 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -486,6 +486,13 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
         goto out;
     }
 
+    if (offset_into_cluster(s, l2_offset)) {
+        qcow2_signal_corruption(bs, true, -1, -1, "L2 table offset %#" PRIx64
+                                " unaligned (L1 index: %#" PRIx64 ")",
+                                l2_offset, l1_index);
+        return -EIO;
+    }
+
     /* load the l2 table in memory */
 
     ret = l2_load(bs, l2_offset, &l2_table);
@@ -508,8 +515,11 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
         break;
     case QCOW2_CLUSTER_ZERO:
         if (s->qcow_version < 3) {
-            qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);
-            return -EIO;
+            qcow2_signal_corruption(bs, true, -1, -1, "Zero cluster entry found"
+                                    " in pre-v3 image (L2 offset: %#" PRIx64
+                                    ", L2 index: %#x)", l2_offset, l2_index);
+            ret = -EIO;
+            goto fail;
         }
         c = count_contiguous_clusters(nb_clusters, s->cluster_size,
                 &l2_table[l2_index], QCOW_OFLAG_ZERO);
@@ -525,6 +535,14 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
         c = count_contiguous_clusters(nb_clusters, s->cluster_size,
                 &l2_table[l2_index], QCOW_OFLAG_ZERO);
         *cluster_offset &= L2E_OFFSET_MASK;
+        if (offset_into_cluster(s, *cluster_offset)) {
+            qcow2_signal_corruption(bs, true, -1, -1, "Data cluster offset %#"
+                                    PRIx64 " unaligned (L2 offset: %#" PRIx64
+                                    ", L2 index: %#x)", *cluster_offset,
+                                    l2_offset, l2_index);
+            ret = -EIO;
+            goto fail;
+        }
         break;
     default:
         abort();
@@ -541,6 +559,10 @@ out:
     *num = nb_available - index_in_cluster;
 
     return ret;
+
+fail:
+    qcow2_cache_put(bs, s->l2_table_cache, (void **)&l2_table);
+    return ret;
 }
 
 /*
@@ -576,6 +598,12 @@ static int get_cluster_table(BlockDriverState *bs, uint64_t offset,
 
     assert(l1_index < s->l1_size);
     l2_offset = s->l1_table[l1_index] & L1E_OFFSET_MASK;
+    if (offset_into_cluster(s, l2_offset)) {
+        qcow2_signal_corruption(bs, true, -1, -1, "L2 table offset %#" PRIx64
+                                " unaligned (L1 index: %#" PRIx64 ")",
+                                l2_offset, l1_index);
+        return -EIO;
+    }
 
     /* seek the l2 table of the given l2 offset */
 
@@ -948,6 +976,15 @@ static int handle_copied(BlockDriverState *bs, uint64_t guest_offset,
         bool offset_matches =
             (cluster_offset & L2E_OFFSET_MASK) == *host_offset;
 
+        if (offset_into_cluster(s, cluster_offset & L2E_OFFSET_MASK)) {
+            qcow2_signal_corruption(bs, true, -1, -1, "Data cluster offset "
+                                    "%#llx unaligned (guest offset: %#" PRIx64
+                                    ")", cluster_offset & L2E_OFFSET_MASK,
+                                    guest_offset);
+            ret = -EIO;
+            goto out;
+        }
+
         if (*host_offset != 0 && !offset_matches) {
             *bytes = 0;
             ret = 0;
@@ -979,7 +1016,7 @@ out:
 
     /* Only return a host offset if we actually made progress. Otherwise we
      * would make requirements for handle_alloc() that it can't fulfill */
-    if (ret) {
+    if (ret > 0) {
         *host_offset = (cluster_offset & L2E_OFFSET_MASK)
                      + offset_into_cluster(s, guest_offset);
     }