qcow2: Don't open images with header.refcount_table_clusters == 0

qcow2_do_open() is checking that header.refcount_table_clusters is not too large, but it doesn't check that it's greater than zero. Apart from the fact that an image like that is obviously corrupted, trying to use it crashes QEMU since we end up with a null s->refcount_table after qcow2_refcount_init(). These images can however be repaired, so allow opening them if the BDRV_O_CHECK flag is set. Signed-off-by: Alberto Garcia <[email protected]> Reviewed-by: Max Reitz <[email protected]> Message-id: f9750f50c80359babba11062e88f5075a47e8e16.1509718618.git.berto@igalia.com Signed-off-by: Max Reitz <[email protected]>
open-power-host-os · Nov 14, 2017 · 951053a · 951053a
1 parent 8aa3483
commit 951053a
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diff --git a/block/qcow2.c b/block/qcow2.c
@@ -1280,6 +1280,12 @@ static int qcow2_do_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
+    if (header.refcount_table_clusters == 0 && !(flags & BDRV_O_CHECK)) {
+        error_setg(errp, "Image does not contain a reference count table");
+        ret = -EINVAL;
+        goto fail;
+    }
+
     ret = validate_table_offset(bs, s->refcount_table_offset,
                                 s->refcount_table_size, sizeof(uint64_t));
     if (ret < 0) {

diff --git a/tests/qemu-iotests/060 b/tests/qemu-iotests/060
@@ -270,6 +270,13 @@ poke_file "$TEST_IMG" "$rb_offset"        "\x00\x00\x00\x00\x00\x00\x00\x00"
 # write will try to allocate a compressed data cluster at offset 0.
 $QEMU_IO -c "write -c 0k 64k" "$TEST_IMG" | _filter_qemu_io
 
+echo
+echo "=== Testing zero refcount table size ==="
+echo
+_make_test_img 64M
+poke_file "$TEST_IMG" "56"                "\x00\x00\x00\x00"
+$QEMU_IO -c "write 0 64k" "$TEST_IMG" 2>&1 | _filter_testdir | _filter_imgfmt
+
 # success, all done
 echo "*** done"
 rm -f $seq.full

diff --git a/tests/qemu-iotests/060.out b/tests/qemu-iotests/060.out
@@ -203,4 +203,9 @@ wrote 65536/65536 bytes at offset 65536
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 qcow2: Marking image as corrupt: Preventing invalid allocation of compressed cluster at offset 0; further corruption events will be suppressed
 write failed: Input/output error
+
+=== Testing zero refcount table size ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864
+can't open device TEST_DIR/t.IMGFMT: Image does not contain a reference count table
 *** done