Copyright (c) 2008 David Malone All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or othe...
NAMEaccf_dns - buffer incoming DNS requests until the whole first request is present
DESCRIPTIONThis is a filter to be placed on a socket that will be using Fn accept to receive incoming connections.
It prevents the application from receiving the connected descriptor via Fn accept until a whole DNS request is available on the socket. It does this by reading the first two bytes of the request, to determine its size, and waiting until the required amount of data is available to be read.
The Fa ACCEPT_FILTER_DNS kernel option is also a module that can be enabled at runtime via kldload(8) if the INET option has been compiled into the kernel.
EXAMPLESIf the sysctl Cm net.inet.tcp.syncookies module is available in the kernel, the following code will enable the DNS accept filter on a socket Fa sok .
struct accept_filter_arg afa; bzero(&afa, sizeof(afa)); strcpy(afa.af_name, "dnsready"); setsockopt(sok, SOL_SOCKET, SO_ACCEPTFILTER, &afa, sizeof(afa));