io_uring/msg_ring: check file type before putting

If we're invoked with a fixed file, follow the normal rules of not
calling io_fput_file(). Fixed files are permanently registered to the
ring, and do not need putting separately.

Cc: stable@vger.kernel.org
Fixes: aa184e86 ("io_uring: don't attempt to IOPOLL for MSG_RING requests")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/msg_ring.c

@@ -165,7 +165,8 @@ int io_msg_ring(struct io_kiocb *req, unsigned int issue_flags)
 		req_set_fail(req);
 	io_req_set_res(req, ret, 0);
 	/* put file to avoid an attempt to IOPOLL the req */
-	io_put_file(req->file);
+	if (!(req->flags & REQ_F_FIXED_FILE))
+		io_put_file(req->file);
 	req->file = NULL;
 	return IOU_OK;
 }