qcow2: Validate refcount table offset

The end of the refcount table must not exceed INT64_MAX so that integer
overflows are avoided.

Also check for misaligned refcount table. Such images are invalid and
probably the result of data corruption. Error out to avoid further
corruption.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

3 files changed, 56 insertions, 0 deletions

diff --git a/block/qcow2.c b/block/qcow2.c
index b9b6e70264..37a332fee5 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -329,6 +329,32 @@ static int qcow2_check(BlockDriverState *bs, BdrvCheckResult *result,
     return ret;
 }
 
+static int validate_table_offset(BlockDriverState *bs, uint64_t offset,
+                                 uint64_t entries, size_t entry_len)
+{
+    BDRVQcowState *s = bs->opaque;
+    uint64_t size;
+
+    /* Use signed INT64_MAX as the maximum even for uint64_t header fields,
+     * because values will be passed to qemu functions taking int64_t. */
+    if (entries > INT64_MAX / entry_len) {
+        return -EINVAL;
+    }
+
+    size = entries * entry_len;
+
+    if (INT64_MAX - size < offset) {
+        return -EINVAL;
+    }
+
+    /* Tables must be cluster aligned */
+    if (offset & (s->cluster_size - 1)) {
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
 static QemuOptsList qcow2_runtime_opts = {
     .name = "qcow2",
     .head = QTAILQ_HEAD_INITIALIZER(qcow2_runtime_opts.head),
@@ -590,6 +616,13 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
+    ret = validate_table_offset(bs, s->refcount_table_offset,
+                                s->refcount_table_size, sizeof(uint64_t));
+    if (ret < 0) {
+        error_setg(errp, "Invalid reference count table offset");
+        goto fail;
+    }
+
     s->snapshots_offset = header.snapshots_offset;
     s->nb_snapshots = header.nb_snapshots;
 
diff --git a/tests/qemu-iotests/080 b/tests/qemu-iotests/080
index 6179e0519f..f58ac736b7 100755
--- a/tests/qemu-iotests/080
+++ b/tests/qemu-iotests/080
@@ -45,6 +45,7 @@ _supported_os Linux
 header_size=104
 
 offset_backing_file_offset=8
+offset_refcount_table_offset=48
 offset_refcount_table_clusters=56
 offset_header_size=100
 offset_ext_magic=$header_size
@@ -76,6 +77,18 @@ poke_file "$TEST_IMG" "$offset_refcount_table_clusters" "\xff\xff\xff\xff"
 poke_file "$TEST_IMG" "$offset_refcount_table_clusters" "\x00\x02\x00\x01"
 { $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
 
+echo
+echo "== Misaligned refcount table =="
+_make_test_img 64M
+poke_file "$TEST_IMG" "$offset_refcount_table_offset" "\x12\x34\x56\x78\x90\xab\xcd\xef"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+
+echo
+echo "== Huge refcount offset =="
+_make_test_img 64M
+poke_file "$TEST_IMG" "$offset_refcount_table_offset" "\xff\xff\xff\xff\xff\xff\x00\x00"
+poke_file "$TEST_IMG" "$offset_refcount_table_clusters" "\x00\x00\x00\x7f"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
 
 # success, all done
 echo "*** done"
diff --git a/tests/qemu-iotests/080.out b/tests/qemu-iotests/080.out
index 6fef6d9892..f919b58d83 100644
--- a/tests/qemu-iotests/080.out
+++ b/tests/qemu-iotests/080.out
@@ -20,4 +20,14 @@ qemu-io: can't open device TEST_DIR/t.qcow2: Reference count table too large
 no file open, try 'help open'
 qemu-io: can't open device TEST_DIR/t.qcow2: Reference count table too large
 no file open, try 'help open'
+
+== Misaligned refcount table ==
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
+qemu-io: can't open device TEST_DIR/t.qcow2: Invalid reference count table offset
+no file open, try 'help open'
+
+== Huge refcount offset ==
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
+qemu-io: can't open device TEST_DIR/t.qcow2: Invalid reference count table offset
+no file open, try 'help open'
 *** done