45159fa631
change pfil_add_hook to put output filters at the tail of the queue, while continuing to place input filters at the head of the queue. update the two users of these functions, and document these changes. fixes PR#4593.
124 lines
3.9 KiB
Groff
124 lines
3.9 KiB
Groff
.\" $NetBSD: pfil.9,v 1.8 1998/03/19 15:47:25 mrg Exp $
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.\"
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.\" Copyright (c) 1996 Matthew R. Green
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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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.\" 3. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Dd August 4, 1996
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.Dt PFIL 9
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.Os NetBSD
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.Sh NAME
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.Nm pfil ,
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.Nm pfil_hook_get ,
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.Nm pfil_add_hook ,
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.Nm pfil_remove_hook
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.Nd packet filter interface
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.Sh SYNOPSIS
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.Fd #include <sys/param.h>
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.Fd #include <netinet/ip.h>
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.Ft struct packet_filter_hook *
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.Fn pfil_hook_get int
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.Ft void
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.Fn pfil_add_hook "int (*func)()" "int flags"
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.Ft void
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.Fn pfil_remove_hook "int (*func)()" "int flags"
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.\"(void *, int, struct ifnet *, int, struct mbuf **)
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.Sh DESCRIPTION
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The
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.Nm
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interface allows a function to be called on every incoming or outgoing
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packets. The hooks for these are embedded in the
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.Fn ip_input
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and
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.Fn ip_output
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routines. The
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.Fn pfil_hook_get
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function returns the first member of a particular hook, either the in or out
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list. The
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.Fn pfil_add_hook
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function takes a function of the form below as it's first argument, and the
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flags for which lists to add the function to. The possible values for these
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flags are some combination of PFIL_IN and PFIL_OUT. The
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.Fn pfil_remove_hook
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removes a hook from the specified lists.
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.Pp
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The
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.Va func
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argument is a function with the following prototype.
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.Pp
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.Fn func "void *data" "int hlen" "struct ifnet *net" "int dir" "struct mbuf **m"
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.Pp
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The
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.Va data
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describes the packet. Currently, this may only be a pointer to a ip structure. The
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.Va net
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and
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.Va m
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arguments describe the network interface and the mbuf holding data for this
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packet. The
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.Va dir
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is the direction; 0 for incoming packets and 1 for outgoing packets. if the function
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returns non-zero, this signals an error and no further processing of this packet is
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performed. The function should set errno to indicate the nature of the error.
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It is the hook's responsibiliy to free the chain if the packet is being dropped.
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.Pp
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The
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.Nm
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interface is enabled in the kernel via the
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.Sy PFIL_HOOKS
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option.
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.Sh RETURN VALUES
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If successful
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.Fn pfil_hook_get
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returns the first member of the packet filter list,
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.Fn pfil_add_hook
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and
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.Fn pfil_remove_hook
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are expected to always succeed.
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.Sh HISTORY
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The
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.Nm
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interface first appeared in
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.Nx 1.3
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The
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.Nm
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input and output lists were originally implemented as
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.Fd <sys/queue.h>
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.Dv LIST
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structures;
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however this was changed in
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.Nx 1.4
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to
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.Dv TAILQ
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structures. This change was to allow the input and output filters to be
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processed in reverse order, to allow the same path to be taken, in or out
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of the kernel.
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.Sh BUGS
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The current
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.Nm
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implementation will need changes to suit a threaded kernel model.
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.Sh SEE ALSO
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.Xr bpf 4 .
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