qcow1: Stricter backing file length check

Like qcow2 since commit 6d33e8e, error out on invalid lengths instead
of silently truncating them to 1023.

Also don't rely on bdrv_pread() catching integer overflows that make len
negative, but use unsigned variables in the first place.

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
(cherry picked from commit d66e5ce)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

block/qcow.c

@@ -97,7 +97,8 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
                      Error **errp)
 {
     BDRVQcowState *s = bs->opaque;
-    int len, i, shift, ret;
+    unsigned int len, i, shift;
+    int ret;
     QCowHeader header;
 
     ret = bdrv_pread(bs->file, 0, &header, sizeof(header));
@@ -199,7 +200,9 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
     if (header.backing_file_offset != 0) {
         len = header.backing_file_size;
         if (len > 1023) {
-            len = 1023;
+            error_setg(errp, "Backing file name too long");
+            ret = -EINVAL;
+            goto fail;
         }
         ret = bdrv_pread(bs->file, header.backing_file_offset,
                    bs->backing_file, len);

tests/qemu-iotests/092

@@ -43,6 +43,8 @@ _supported_fmt qcow
 _supported_proto generic
 _supported_os Linux
 
+offset_backing_file_offset=8
+offset_backing_file_size=16
 offset_size=24
 offset_cluster_bits=32
 offset_l2_bits=33
@@ -81,6 +83,15 @@ poke_file "$TEST_IMG" "$offset_size" "\xee\xee\xee\xee\xee\xee\xee\xee"
 poke_file "$TEST_IMG" "$offset_size" "\x7f\xff\xff\xff\xff\xff\xff\xff"
 { $QEMU_IO -c "write 0 64M" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
 
+echo
+echo "== Invalid backing file length =="
+_make_test_img 64M
+poke_file "$TEST_IMG" "$offset_backing_file_offset" "\x00\x00\x00\xff"
+poke_file "$TEST_IMG" "$offset_backing_file_size" "\xff\xff\xff\xff"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+poke_file "$TEST_IMG" "$offset_backing_file_size" "\x7f\xff\xff\xff"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+
 # success, all done
 echo "*** done"
 rm -f $seq.full

tests/qemu-iotests/092.out

@@ -28,4 +28,11 @@ qemu-io: can't open device TEST_DIR/t.qcow: Image too large
 no file open, try 'help open'
 qemu-io: can't open device TEST_DIR/t.qcow: Image too large
 no file open, try 'help open'
+
+== Invalid backing file length ==
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
+qemu-io: can't open device TEST_DIR/t.qcow: Backing file name too long
+no file open, try 'help open'
+qemu-io: can't open device TEST_DIR/t.qcow: Backing file name too long
+no file open, try 'help open'
 *** done