io_uring/net: don't update msg_name if not provided

io_sendmsg_copy_hdr() may clear msg->msg_name if the userspace didn't
provide it, we should retain NULL in this case.

Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/97d49f61b5ec76d0900df658cfde3aa59ff22121.1664486545.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/net.c

@@ -164,6 +164,7 @@ static int io_setup_async_msg(struct io_kiocb *req,
 	}
 	req->flags |= REQ_F_NEED_CLEANUP;
 	memcpy(async_msg, kmsg, sizeof(*kmsg));
+	if (async_msg->msg.msg_name)
 		async_msg->msg.msg_name = &async_msg->addr;
 	/* if were using fast_iov, set it to the new one */
 	if (!kmsg->free_iov) {