[PATCH 2/4] qemu-img: fix offset calculation in bench

[gerben@altlinux.org]

From: Denis Rastyogin <gerben@altlinux.org>

This error was discovered by fuzzing qemu-img.

The current offset calculation leads to an EIO error
in block/block-backend.c: blk_check_byte_request():

 if (offset > len || len - offset < bytes) {
     return -EIO;
 }

This triggers the error message:
"qemu-img: Failed request: Input/output error".

Example of the issue:
 offset: 260076
 len: 260096
 bytes: 4096

This fix ensures that offset remains within a valid range.

Signed-off-by: Denis Rastyogin <gerben@altlinux.org>
---
 qemu-img.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/qemu-img.c b/qemu-img.c
index 2044c22a4c..71c9fe496f 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -4491,7 +4491,7 @@ static void bench_cb(void *opaque, int ret)
         if (b->image_size == 0) {
             b->offset = 0;
         } else {
-            b->offset %= b->image_size;
+            b->offset %= b->image_size - b->bufsize;
         }
         if (b->write) {
             acb = blk_aio_pwritev(b->blk, offset, b->qiov, 0, bench_cb, b);
-- 
2.42.2