1.\" $NetBSD: pfil.9,v 1.24 2004/01/01 15:24:35 wiz Exp $ 2.\" 3.\" Copyright (c) 1996 Matthew R. Green 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. The name of the author may not be used to endorse or promote products 15.\" derived from this software without specific prior written permission. 16.\" 17.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 18.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 21.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 22.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 23.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 24.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 25.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27.\" SUCH DAMAGE. 28.\" 29.Dd January 16, 2015 30.Dt PFIL 9 31.Os 32.Sh NAME 33.Nm pfil , 34.Nm pfil_head_register , 35.Nm pfil_head_unregister , 36.Nm pfil_head_get , 37.Nm pfil_add_hook , 38.Nm pfil_remove_hook , 39.Nm pfil_run_hooks 40.Nd packet filter interface 41.Sh SYNOPSIS 42.In sys/param.h 43.In sys/mbuf.h 44.In net/if.h 45.In net/pfil.h 46.Ft typedef int 47.Fn (*pfil_func_t) "void *arg" "struct mbuf **mp" "struct ifnet *ifp" "int dir" 48.Ft int 49.Fn pfil_head_register "struct pfil_head *ph" 50.Ft int 51.Fn pfil_head_unregister "struct pfil_head *pfh" 52.Ft struct pfil_head * 53.Fn pfil_head_get "int type" "u_long val" 54.Ft int 55.Fn pfil_add_hook "pfil_func_t func" "void *arg" "int flags" "struct pfil_head *ph" 56.Ft int 57.Fn pfil_remove_hook "pfil_func_t func" "void *arg" "int flags" "struct pfil_head *ph" 58.Ft int 59.Fn pfil_run_hooks "struct pfil_head *ph" "struct mbuf **mp" "struct ifnet *ifp" "int dir" 60.Sh DESCRIPTION 61The 62.Nm 63framework allows for a specified function to be invoked for every 64incoming or outgoing packet for a particular network I/O stream. 65These hooks may be used to implement a firewall or perform packet 66transformations. 67.Pp 68Packet filtering points are registered with 69.Fn pfil_head_register . 70Filtering points are identified by a key (void *) and a data link type 71(int) in the 72.Em pfil_head 73structure. 74Packet filters use the key and data link type to look up the filtering 75point with which they register themselves. 76The key is unique to the filtering point. 77The data link type is a 78.Xr bpf 4 79DLT constant indicating what kind of header is present on the packet 80at the filtering point. 81Filtering points may be unregistered with the 82.Fn pfil_head_unregister 83function. 84.Pp 85Packet filters register/unregister themselves with a filtering point 86with the 87.Fn pfil_add_hook 88and 89.Fn pfil_remove_hook 90functions, respectively. 91The head is looked up using the 92.Fn pfil_head_get 93function, which takes the key and data link type that the packet filter 94expects. 95Filters may provide an argument to be passed to the filter when 96invoked on a packet. 97.Pp 98When a filter is invoked, the packet appears just as if it 99.Dq came off the wire . 100That is, all protocol fields are in network byte order. 101The filter is called with its specified argument, the pointer to the 102pointer to the mbuf containing the packet, the pointer to the network 103interface that the packet is traversing, and the direction 104.Dv ( PFIL_IN 105or 106.Dv PFIL_OUT , 107see also below) that the packet is traveling. 108The filter may change which mbuf the mbuf ** argument references. 109The filter returns an 110.Va errno 111if the packet processing is to stop, or 0 if the processing is to continue. 112If the packet processing is to stop, it is the responsibility of the 113filter to free the packet. 114.Pp 115The 116.Em flags 117parameter, used in the 118.Fn pfil_add_hook 119and 120.Fn pfil_remove_hook 121functions, indicates when the filter should be called. 122The flags are: 123.Bl -tag -offset indent -width ".Dv PFIL_OUT" -compact 124.It Dv PFIL_IN 125call me on incoming packets 126.It Dv PFIL_OUT 127call me on outgoing packets 128.It Dv PFIL_ALL 129call me on all of the above 130.El 131.Sh SEE ALSO 132.Xr bpf 4 133.Sh HISTORY 134The 135.Nm 136interface first appeared in 137.Nx 1.3 . 138The 139.Nm 140input and output lists were originally implemented as 141.In sys/queue.h 142.Dv LIST 143structures; 144however this was changed in 145.Nx 1.4 146to 147.Dv TAILQ 148structures. 149This change was to allow the input and output filters to be processed in 150reverse order, to allow the same path to be taken, in or out of the kernel. 151.Pp 152The 153.Nm 154interface was changed in 1.4T to accept a 3rd parameter to both 155.Fn pfil_add_hook 156and 157.Fn pfil_remove_hook , 158introducing the capability of per-protocol filtering. 159This was done primarily in order to support filtering of IPv6. 160.Pp 161In 1.5K, the 162.Nm 163framework was changed to work with an arbitrary number of filtering points, 164as well as be less IP-centric. 165.Pp 166The 167.Nm 168interface was imported from 169.Nx 170into 171.Dx 1.0 172and was reworked to suit a threaded kernel model in 173.Dx 2.1 . 174.Sh AUTHORS 175The 176.Nm 177interface was designed and implemented by Matthew R. Green, with help 178from Darren Reed, Jason R. Thorpe and Charles M. Hannum. 179Darren Reed added support for IPv6 in addition to IPv4. 180Jason R. Thorpe added support for multiple hooks and other clean up. 181