io_uring: statx/openat/openat2 don't support fixed files

mainline inclusion
from mainline-5.6-rc2
commit cf3040ca
category: feature
bugzilla: https://bugzilla.openeuler.org/show_bug.cgi?id=27
CVE: NA
---------------------------

All of these opcodes take a directory file descriptor. We can't easily
support fixed files for these operations, and the use case for that
probably isn't all that clear (or sensible) anyway.

Disable IOSQE_FIXED_FILE for these operations.
Reported-by: NStefan Metzmacher <metze@samba.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Conflicts:
	fs/io_uring.c
[skip openat2 for commit cebdb986
 ("io_uring: add support for IORING_OP_OPENAT2") is not applied]
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

@@ -2511,6 +2511,8 @@ static int io_openat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 	if (sqe->ioprio || sqe->buf_index)
 		return -EINVAL;
+	if (sqe->flags & IOSQE_FIXED_FILE)
+		return -EBADF;
 
 	req->open.dfd = READ_ONCE(sqe->fd);
 	req->open.mode = READ_ONCE(sqe->len);
@@ -2688,6 +2690,8 @@ static int io_statx_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 	if (sqe->ioprio || sqe->buf_index)
 		return -EINVAL;
+	if (sqe->flags & IOSQE_FIXED_FILE)
+		return -EBADF;
 
 	req->open.dfd = READ_ONCE(sqe->fd);
 	req->open.mask = READ_ONCE(sqe->len);
@@ -2761,7 +2765,7 @@ static int io_close_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	    sqe->rw_flags || sqe->buf_index)
 		return -EINVAL;
 	if (sqe->flags & IOSQE_FIXED_FILE)
-		return -EINVAL;
+		return -EBADF;
 
 	req->close.fd = READ_ONCE(sqe->fd);
 	if (req->file->f_op == &io_uring_fops ||