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>

diff --git a/block/qcow2.c b/block/qcow2.c
index b9b6e70264fad5f4d24e4c798efd3ef20e664fcc..37a332fee54d6e773c55aa1d88a156d67a3c8d90 100644 (file)
--- 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 6179e0519f01228d67d75cdf9c291a9bdfa606d7..f58ac736b7596f738a2322d560fd1815a52a62c0 100755 (executable)
--- 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 6fef6d989279f6981bbbf4e06de238a37c61e194..f919b58d839efce3614e9552a9c37e8053fddc3c 100644 (file)
--- 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