man/man9/pfil.9

.\"	$NetBSD: pfil.9,v 1.24 2004/01/01 15:24:35 wiz Exp $
.\"
.\" Copyright (c) 1996 Matthew R. Green
.\" 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 other materials provided with the distribution.
.\" 3. The name of the author may not be used to endorse or promote products
.\"    derived from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd January 16, 2015
.Dt PFIL 9
.Os
.Sh NAME
.Nm pfil ,
.Nm pfil_head_register ,
.Nm pfil_head_unregister ,
.Nm pfil_head_get ,
.Nm pfil_add_hook ,
.Nm pfil_remove_hook ,
.Nm pfil_run_hooks
.Nd packet filter interface
.Sh SYNOPSIS
.In sys/param.h
.In sys/mbuf.h
.In net/if.h
.In net/pfil.h
.Ft typedef int
.Fn (*pfil_func_t) "void *arg" "struct mbuf **mp" "struct ifnet *ifp" "int dir"
.Ft int
.Fn pfil_head_register "struct pfil_head *ph"
.Ft int
.Fn pfil_head_unregister "struct pfil_head *pfh"
.Ft struct pfil_head *
.Fn pfil_head_get "int type" "u_long val"
.Ft int
.Fn pfil_add_hook "pfil_func_t func" "void *arg" "int flags" "struct pfil_head *ph"
.Ft int
.Fn pfil_remove_hook "pfil_func_t func" "void *arg" "int flags" "struct pfil_head *ph"
.Ft int
.Fn pfil_run_hooks "struct pfil_head *ph" "struct mbuf **mp" "struct ifnet *ifp" "int dir"
.Sh DESCRIPTION
The
.Nm
framework allows for a specified function to be invoked for every
incoming or outgoing packet for a particular network I/O stream.
These hooks may be used to implement a firewall or perform packet
transformations.
.Pp
Packet filtering points are registered with
.Fn pfil_head_register .
Filtering points are identified by a key (void *) and a data link type
(int) in the
.Em pfil_head
structure.
Packet filters use the key and data link type to look up the filtering
point with which they register themselves.
The key is unique to the filtering point.
The data link type is a
.Xr bpf 4
DLT constant indicating what kind of header is present on the packet
at the filtering point.
Filtering points may be unregistered with the
.Fn pfil_head_unregister
function.
.Pp
Packet filters register/unregister themselves with a filtering point
with the
.Fn pfil_add_hook
and
.Fn pfil_remove_hook
functions, respectively.
The head is looked up using the
.Fn pfil_head_get
function, which takes the key and data link type that the packet filter
expects.
Filters may provide an argument to be passed to the filter when
invoked on a packet.
.Pp
When a filter is invoked, the packet appears just as if it
.Dq came off the wire .
That is, all protocol fields are in network byte order.
The filter is called with its specified argument, the pointer to the
pointer to the mbuf containing the packet, the pointer to the network
interface that the packet is traversing, and the direction
.Dv ( PFIL_IN
or
.Dv PFIL_OUT ,
see also below) that the packet is traveling.
The filter may change which mbuf the mbuf ** argument references.
The filter returns an
.Va errno
if the packet processing is to stop, or 0 if the processing is to continue.
If the packet processing is to stop, it is the responsibility of the
filter to free the packet.
.Pp
The
.Em flags
parameter, used in the
.Fn pfil_add_hook
and
.Fn pfil_remove_hook
functions, indicates when the filter should be called.
The flags are:
.Bl -tag -offset indent -width ".Dv PFIL_OUT" -compact
.It Dv PFIL_IN
call me on incoming packets
.It Dv PFIL_OUT
call me on outgoing packets
.It Dv PFIL_ALL
call me on all of the above
.El
.Sh SEE ALSO
.Xr bpf 4
.Sh HISTORY
The
.Nm
interface first appeared in
.Nx 1.3 .
The
.Nm
input and output lists were originally implemented as
.In sys/queue.h
.Dv LIST
structures;
however this was changed in
.Nx 1.4
to
.Dv TAILQ
structures.
This change was to allow the input and output filters to be processed in
reverse order, to allow the same path to be taken, in or out of the kernel.
.Pp
The
.Nm
interface was changed in 1.4T to accept a 3rd parameter to both
.Fn pfil_add_hook
and
.Fn pfil_remove_hook ,
introducing the capability of per-protocol filtering.
This was done primarily in order to support filtering of IPv6.
.Pp
In 1.5K, the
.Nm
framework was changed to work with an arbitrary number of filtering points,
as well as be less IP-centric.
.Pp
The
.Nm
interface was imported from
.Nx
into
.Dx 1.0
and was reworked to suit a threaded kernel model in
.Dx 2.1 .
.Sh AUTHORS
.An -nosplit
The
.Nm
interface was designed and implemented by
.An Matthew R. Green ,
with help from
.An Darren Reed ,
.An Jason R. Thorpe
and
.An Charles M. Hannum .
.An Darren Reed
added support for IPv6 in addition to IPv4.
.An Jason R. Thorpe
added support for multiple hooks and other clean up.