b252313f0b
The KPI have been reviewed and cleansed of features that were planned back 20 years ago and never implemented. The pfil(9) internals have been made opaque to protocols with only returned types and function declarations exposed. The KPI is made more strict, but at the same time more extensible, as kernel uses same command structures that userland ioctl uses. In nutshell [KA]PI is about declaring filtering points, declaring filters and linking and unlinking them together. New [KA]PI makes it possible to reconfigure pfil(9) configuration: change order of hooks, rehook filter from one filtering point to a different one, disconnect a hook on output leaving it on input only, prepend/append a filter to existing list of filters. Now it possible for a single packet filter to provide multiple rulesets that may be linked to different points. Think of per-interface ACLs in Cisco or Juniper. None of existing packet filters yet support that, however limited usage is already possible, e.g. default ruleset can be moved to single interface, as soon as interface would pride their filtering points. Another future feature is possiblity to create pfil heads, that provide not an mbuf pointer but just a memory pointer with length. That would allow filtering at very early stages of a packet lifecycle, e.g. when packet has just been received by a NIC and no mbuf was yet allocated. Differential Revision: https://reviews.freebsd.org/D18951
165 lines
4.6 KiB
Groff
165 lines
4.6 KiB
Groff
.\" $NetBSD: pfil.9,v 1.22 2003/07/01 13:04:06 wiz Exp $
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.\"
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.\" Copyright (c) 2019 Gleb Smirnoff <glebius@FreeBSD.org>
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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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.\" $FreeBSD$
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.\"
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.Dd January 28, 2019
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.Dt PFIL 9
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.Os
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.Sh NAME
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.Nm pfil ,
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.Nm pfil_head_register ,
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.Nm pfil_head_unregister ,
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.Nm pfil_link ,
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.Nm pfil_run_hooks
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.Nd packet filter interface
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/mbuf.h
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.In net/pfil.h
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.Ft pfil_head_t
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.Fn pfil_head_register "struct pfil_head_args *args"
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.Ft void
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.Fn pfil_head_unregister "struct pfil_head_t *head"
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.Ft pfil_hook_t
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.Fn pfil_add_hook "struct pfil_hook_args *"
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.Ft void
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.Fn pfil_remove_hook "pfil_hook_t"
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.Ft int
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.Fn pfil_link "struct pfil_link_args *args"
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.Ft int
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.Fn pfil_run_hooks "phil_head_t *" "pfil_packet_t" "struct ifnet *" "int" "struct inpcb *"
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.Sh DESCRIPTION
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The
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.Nm
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framework allows for a specified function or a list of functions
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to be invoked for every incoming or outgoing packet for a particular
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network I/O stream.
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These hooks may be used to implement a firewall or perform packet
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transformations.
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.Pp
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Packet filtering points, for historical reasons named
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.Em heads ,
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are registered with
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.Fn pfil_head_register .
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The function is supplied with special versioned
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.Vt struct pfil_head_args
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structure that specifies type and features of the head as well as
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human readable name.
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If the filtering point to be ever destroyed, the subsystem that
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created it must unregister it with call to
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.Fn pfil_head_unregister .
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.Pp
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Packet filtering systems may register arbitrary number of filters,
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for historical reasons named
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.Em hooks .
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To register a new hook
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.Fn pfil_add_hook
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with special versioned
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.Vt struct pfil_hook_args
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structure is called.
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The structure specifies type and features of the hook, pointer to
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the actual filtering function and user readable name of the filtering
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module and ruleset name.
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Later hooks can be removed with
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.Fn pfil_remove_hook
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functions.
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.Pp
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To connect existing
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.Em hook
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to an existing
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.Em head
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function
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.Fn pfil_link
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shall be used.
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The function is supplied with versioned
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.Vt struct pfil_link_args
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structure that specifies either literal names of hook and head or
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pointers to them.
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Typically
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.Fn pfil_link
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is called by filtering modules to autoregister their default ruleset
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and default filtering points.
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It also serves on the kernel side of
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.Xr ioctl 2
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when user changes
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.Nm
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configuration with help of
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.Xr pfilctl 8
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utility.
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.Pp
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For every packet traveling through a
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.Em head
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the latter shall invoke
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.Fn pfil_run_hooks .
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The function can accept either
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.Vt struct mbuf *
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pointer or a
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.Vt void *
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pointer and length.
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In case if a hooked filtering module cannot understand
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.Vt void *
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pointer
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.Nm
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will provide it with a fake one.
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All calls to
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.Fn pfil_run_hooks
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are performed in network
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.Xr epoch 9 .
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.Sh HEADS (filtering points)
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By default kernel creates the following heads:
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.Bl -tag -width "ethernet"
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.It inet
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IPv4 packets.
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.It inet6
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IPv6 packets.
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.It ethernet
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Link-layer packets.
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.El
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.Pp
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Default rulesets are automatically linked to these heads to preserve
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historical behavavior.
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.Sh SEE ALSO
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.Xr ipfilter 4 ,
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.Xr ipfw 4 ,
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.Xr pf 4 ,
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.Xr pfilctl 8
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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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interface was imported into
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.Fx 5.2 .
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In
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.Fx 13.0
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the interface was significantly rewritten.
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