It's not safe to treat bdrv_is_allocated error as unallocated: if we
mistake we may rewrite guest data.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
---
block/io.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/block/io.c b/block/io.c
index 2ba603c7bc..dccad64d46 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1193,11 +1193,13 @@ static int coroutine_fn
bdrv_co_do_copy_on_readv(BdrvChild *child,
ret = bdrv_is_allocated(bs, cluster_offset,
MIN(cluster_bytes, max_transfer), &pnum);
if (ret < 0) {
- /* Safe to treat errors in querying allocation as if
- * unallocated; we'll probably fail again soon on the
- * read, but at least that will set a decent errno.
+ /*
+ * We must fail here, and can't treat error as allocated or
+ * unallocated: if we mistake, it will lead to not done
copy-on-read
+ * in first case and to rewriting guest data that is already in top
+ * layer in the second case.
*/
- pnum = MIN(cluster_bytes, max_transfer);
+ goto err;
}
/* Stop at EOF if the image ends in the middle of the cluster */
@@ -1208,7 +1210,7 @@ static int coroutine_fn
bdrv_co_do_copy_on_readv(BdrvChild *child,
assert(skip_bytes < pnum);
- if (ret <= 0) {
+ if (ret == 0) {
/* Must copy-on-read; use the bounce buffer */
pnum = MIN(pnum, MAX_BOUNCE_BUFFER);
qemu_iovec_init_buf(&local_qiov, bounce_buffer, pnum);
--
2.18.0
