qcow2: Fix theoretical corruption in store_bitmap() error path

In order to write the bitmap table to the image file, it is converted to
big endian. If the write fails, it is passed to clear_bitmap_table() to
free all of the clusters it had allocated before. However, if we don't
convert it back to native endianness first, we'll free things at a wrong
offset.

In practical terms, the offsets will be so high that we won't actually
free any allocated clusters, but just run into an error, but in theory
this can cause image corruption.

Cc: qemu-stable@nongnu.org
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Message-Id: <20230112191454.169353-2-kwolf@redhat.com>
Reviewed-by: NHanna Czenczek <hreitz@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/qcow2-bitmap.c

@@ -117,7 +117,7 @@ static int update_header_sync(BlockDriverState *bs)
     return bdrv_flush(bs->file->bs);
 }
 
-static inline void bitmap_table_to_be(uint64_t *bitmap_table, size_t size)
+static inline void bitmap_table_bswap_be(uint64_t *bitmap_table, size_t size)
 {
     size_t i;
 
@@ -1403,9 +1403,10 @@ static int store_bitmap(BlockDriverState *bs, Qcow2Bitmap *bm, Error **errp)
         goto fail;
     }
 
-    bitmap_table_to_be(tb, tb_size);
+    bitmap_table_bswap_be(tb, tb_size);
     ret = bdrv_pwrite(bs->file, tb_offset, tb_size * sizeof(tb[0]), tb, 0);
     if (ret < 0) {
+        bitmap_table_bswap_be(tb, tb_size);
         error_setg_errno(errp, -ret, "Failed to write bitmap '%s' to file",
                          bm_name);
         goto fail;