io_uring/net: fix zc fixed buf lifetime

Notifications usually outlive requests, so we need to pin buffers with
it by assigning a rsrc to it instead of the request.

Fixed: b48c312 ("io_uring/net: simplify zerocopy send user API")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/dd6406ff8a90887f2b36ed6205dac9fda17c1f35.1663366886.git.asml.silence@gmail.com
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

io_uring/net.c

@@ -905,22 +905,22 @@ int io_sendzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	if (zc->flags & ~(IORING_RECVSEND_POLL_FIRST |
 			  IORING_RECVSEND_FIXED_BUF))
 		return -EINVAL;
+	notif = zc->notif = io_alloc_notif(ctx);
+	if (!notif)
+		return -ENOMEM;
+	notif->cqe.user_data = req->cqe.user_data;
+	notif->cqe.res = 0;
+	notif->cqe.flags = IORING_CQE_F_NOTIF;
+	req->flags |= REQ_F_NEED_CLEANUP;
 	if (zc->flags & IORING_RECVSEND_FIXED_BUF) {
 		unsigned idx = READ_ONCE(sqe->buf_index);
 
 		if (unlikely(idx >= ctx->nr_user_bufs))
 			return -EFAULT;
 		idx = array_index_nospec(idx, ctx->nr_user_bufs);
 		req->imu = READ_ONCE(ctx->user_bufs[idx]);
-		io_req_set_rsrc_node(req, ctx, 0);
+		io_req_set_rsrc_node(notif, ctx, 0);
 	}
-	notif = zc->notif = io_alloc_notif(ctx);
-	if (!notif)
-		return -ENOMEM;
-	notif->cqe.user_data = req->cqe.user_data;
-	notif->cqe.res = 0;
-	notif->cqe.flags = IORING_CQE_F_NOTIF;
-	req->flags |= REQ_F_NEED_CLEANUP;
 
 	zc->buf = u64_to_user_ptr(READ_ONCE(sqe->addr));
 	zc->len = READ_ONCE(sqe->len);