io_uring: allow AT_FDCWD for non-file openat/openat2/statx

mainline inclusion
from mainline-5.6-rc2
commit 0b5faf6b
category: feature
bugzilla: https://bugzilla.openeuler.org/show_bug.cgi?id=27
CVE: NA
---------------------------

Don't just check for dirfd == -1, we should allow AT_FDCWD as well for
relative lookups.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: Nyangerkun <yangerkun@huawei.com>
Reviewed-by: Nzhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>

fs/io_uring.c

@@ -4479,7 +4479,7 @@ static int io_req_needs_file(struct io_kiocb *req, int fd)
 {
 	if (!io_op_defs[req->opcode].needs_file)
 		return 0;
-	if (fd == -1 && io_op_defs[req->opcode].fd_non_neg)
+	if ((fd == -1 || fd == AT_FDCWD) && io_op_defs[req->opcode].fd_non_neg)
 		return 0;
 	return 1;
 }