io_uring: add IOPOLL and reserved field checks to IORING_OP_UNLINKAT

We can't support IOPOLL with non-pollable request types, and we should
check for unused/reserved fields like we do for other request types.

Fixes: 14a1143b68 ("io_uring: add support for IORING_OP_UNLINKAT")
Cc: stable@vger.kernel.org
Reported-by: Dmitry Kadashev <dkadashev@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -3514,6 +3514,10 @@ static int io_unlinkat_prep(struct io_kiocb *req,
 	struct io_unlink *un = &req->unlink;
 	const char __user *fname;
 
+	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
+	if (sqe->ioprio || sqe->off || sqe->len || sqe->buf_index)
+		return -EINVAL;
 	if (unlikely(req->flags & REQ_F_FIXED_FILE))
 		return -EBADF;