Bug: Example code does not check connection array size

[jonashoechst]

Thank you for the great QUIC implementation! We might have found a bug, though it's only affecting the echo example. The server code crashed in the case if more than 256 connections are handled.

Details: The conns array holds active connections for the instance and is defined by a fixed length:

quicly/examples/echo.c

Line 195 in a9498b4

quicly_conn_t *conns[256] = {client}; /* a null-terminated list of connections; proper app should use a hashmap or something */

In process_msg new connections are accepted and added to the respective list, but the length of this list is not checked:

quicly/examples/echo.c

Lines 176 to 179 in a9498b4

	} else if (!is_client) {
	/* assume that the packet is a new connection */
	quicly_accept(conns + i, &ctx, NULL, msg->msg_name, &decoded, NULL, &next_cid, NULL);
	}