virtio-blk: Fix use after free in error case

virtio_blk_req_complete frees the request, so we can't access it any more when
calling bdrv_mon_event. Use the pointer that was copied earlier.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>

hw/virtio-blk.c

@@ -65,7 +65,7 @@ static int virtio_blk_handle_rw_error(VirtIOBlockReq *req, int error,
     VirtIOBlock *s = req->dev;
 
     if (action == BLOCK_ERR_IGNORE) {
-        bdrv_mon_event(req->dev->bs, BDRV_ACTION_IGNORE, is_read);
+        bdrv_mon_event(s->bs, BDRV_ACTION_IGNORE, is_read);
         return 0;
     }
 
@@ -73,11 +73,11 @@ static int virtio_blk_handle_rw_error(VirtIOBlockReq *req, int error,
             || action == BLOCK_ERR_STOP_ANY) {
         req->next = s->rq;
         s->rq = req;
-        bdrv_mon_event(req->dev->bs, BDRV_ACTION_STOP, is_read);
+        bdrv_mon_event(s->bs, BDRV_ACTION_STOP, is_read);
         vm_stop(0);
     } else {
         virtio_blk_req_complete(req, VIRTIO_BLK_S_IOERR);
-        bdrv_mon_event(req->dev->bs, BDRV_ACTION_REPORT, is_read);
+        bdrv_mon_event(s->bs, BDRV_ACTION_REPORT, is_read);
     }
 
     return 1;