2008-07-18 14:46:01 +00:00
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.\"
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.\" Copyright (c) 2008 David Malone
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.\"
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\" "
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.Dd July 16, 2008
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.Dt ACCF_DNS 9
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2010-04-14 19:08:06 +00:00
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.Os
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2008-07-18 14:46:01 +00:00
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.Sh NAME
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.Nm accf_dns
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.Nd buffer incoming DNS requests until the whole first request is present
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.Sh SYNOPSIS
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.Nm options INET
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.Nm options ACCEPT_FILTER_DNS
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.Nm kldload accf_dns
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.Sh DESCRIPTION
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This is a filter to be placed on a socket that will be using
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.Fn accept
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to receive incoming connections.
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.Pp
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It prevents the application from receiving the connected descriptor via
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.Fn accept
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until a whole DNS request is available on the socket.
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It does this by reading the first two bytes of the request,
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to determine its size,
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and waiting until the required amount of data is available to be read.
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.Pp
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The
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.Fa ACCEPT_FILTER_DNS
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kernel option is also a module that can be enabled at runtime via
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.Xr kldload 8
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if the INET option has been compiled into the kernel.
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.Sh EXAMPLES
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If the
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.Nm
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module is available in the kernel,
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the following code will enable the DNS accept filter
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on a socket
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.Fa sok .
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.Bd -literal -offset 0i
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struct accept_filter_arg afa;
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bzero(&afa, sizeof(afa));
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strcpy(afa.af_name, "dnsready");
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setsockopt(sok, SOL_SOCKET, SO_ACCEPTFILTER, &afa, sizeof(afa));
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.Ed
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.Sh SEE ALSO
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.Xr setsockopt 2 ,
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.Xr accept_filter 9 ,
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.Xr accf_http 9
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.Xr accf_data 9
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.Sh HISTORY
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The accept filter mechanism was introduced in
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.Fx 4.0 .
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.Sh AUTHORS
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This manual page and the filter were written by
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.An David Malone .
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