io_uring/rw: ensure io->bytes_done is always initialized

If IOSQE_ASYNC is set and we fail importing an iovec for a readv or
writev request, then we leave ->bytes_done uninitialized and hence the
eventual failure CQE posted can potentially have a random res value
rather than the expected -EINVAL.

Setup ->bytes_done before potentially failing, so we have a consistent
value if we fail the request early.

Cc: stable@vger.kernel.org
Reported-by: xingwei lee <xrivendell7@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

io_uring/rw.c

@@ -589,15 +589,19 @@ static inline int io_rw_prep_async(struct io_kiocb *req, int rw)
 	struct iovec *iov;
 	int ret;
 
+	iorw->bytes_done = 0;
+	iorw->free_iovec = NULL;
+
 	/* submission path, ->uring_lock should already be taken */
 	ret = io_import_iovec(rw, req, &iov, &iorw->s, 0);
 	if (unlikely(ret < 0))
 		return ret;
 
-	iorw->bytes_done = 0;
-	iorw->free_iovec = iov;
-	if (iov)
+	if (iov) {
+		iorw->free_iovec = iov;
 		req->flags |= REQ_F_NEED_CLEANUP;
+	}
+
 	return 0;
 }