io_uring/sync: validate passed in offset

Check if the passed in offset is negative once cast to sync->off. This
ensures that -EINVAL is returned for that case, like it would be for
sync_file_range(2).

Fixes: c992fe2925 ("io_uring: add fsync support")
Signed-off-by: Jens Axboe <[email protected]>

io_uring/sync.c

@@ -62,6 +62,8 @@ int io_fsync_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		return -EINVAL;
 
 	sync->off = READ_ONCE(sqe->off);
+	if (sync->off < 0)
+		return -EINVAL;
 	sync->len = READ_ONCE(sqe->len);
 	req->flags |= REQ_F_FORCE_ASYNC;
 	return 0;