1.\" $NetBSD: pfil.9,v 1.24 2004/01/01 15:24:35 wiz Exp $ 2.\" $DragonFly: src/share/man/man9/pfil.9,v 1.1 2005/12/21 19:50:54 swildner Exp $ 3.\" 4.\" Copyright (c) 1996 Matthew R. Green 5.\" All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. The name of the author may not be used to endorse or promote products 16.\" derived from this software without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 19.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 20.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 21.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 22.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 23.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 24.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 25.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 26.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.Dd September 26, 2005 31.Dt PFIL 9 32.Os 33.Sh NAME 34.Nm pfil , 35.Nm pfil_head_register , 36.Nm pfil_head_unregister , 37.Nm pfil_head_get , 38.Nm pfil_hook_get , 39.Nm pfil_add_hook , 40.Nm pfil_remove_hook , 41.Nm pfil_run_hooks 42.Nd packet filter interface 43.Sh SYNOPSIS 44.In sys/param.h 45.In sys/mbuf.h 46.In net/if.h 47.In net/pfil.h 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 struct packet_filter_hook * 55.Fn pfil_hook_get "int dir" "struct pfil_head *ph" 56.Ft void 57.Fn pfil_add_hook "int (*func)()" "void *arg" "int flags" "struct pfil_head *ph" 58.Ft void 59.Fn pfil_remove_hook "int (*func)()" "void *arg" "int flags" "struct pfil_head *ph" 60.Ft int 61.Fn (*func) "void *arg" "struct mbuf **mp" "struct ifnet *" "int dir" 62.Ft int 63.Fn pfil_run_hooks "struct pfil_head *ph" "struct mbuf **mp" "struct ifnet *ifp" "int dir" 64.Sh DESCRIPTION 65The 66.Nm 67framework allows for a specified function to be invoked for every 68incoming or outgoing packet for a particular network I/O stream. 69These hooks may be used to implement a firewall or perform packet 70transformations. 71.Pp 72Packet filtering points are registered with 73.Fn pfil_head_register . 74Filtering points are identified by a key (void *) and a data link type 75(int) in the 76.Em pfil_head 77structure. 78Packet filters use the key and data link type to look up the filtering 79point with which they register themselves. 80The key is unique to the filtering point. 81The data link type is a 82.Xr bpf 4 83DLT constant indicating what kind of header is present on the packet 84at the filtering point. 85Filtering points may be unregistered with the 86.Fn pfil_head_unregister 87function. 88.Pp 89Packet filters register/unregister themselves with a filtering point 90with the 91.Fn pfil_add_hook 92and 93.Fn pfil_remove_hook 94functions, respectively. 95The head is looked up using the 96.Fn pfil_head_get 97function, which takes the key and data link type that the packet filter 98expects. 99Filters may provide an argument to be passed to the filter when 100invoked on a packet. 101.Pp 102When a filter is invoked, the packet appears just as if it 103.Dq came off the wire . 104That is, all protocol fields are in network byte order. 105The filter is called with its specified argument, the pointer to the 106pointer to the mbuf containing the packet, the pointer to the network 107interface that the packet is traversing, and the direction 108.Dv ( PFIL_IN 109or 110.Dv PFIL_OUT , 111see also below) that the packet is traveling. 112The filter may change which mbuf the mbuf ** argument references. 113The filter returns an errno if the packet processing is to stop, or 0 114if the processing is to continue. 115If the packet processing is to stop, it is the responsibility of the 116filter to free the packet. 117.Pp 118The 119.Em flags 120parameter, used in the 121.Fn pfil_add_hook 122and 123.Fn pfil_remove_hook 124functions, indicates when the filter should be called. 125The flags are: 126.Bl -tag -offset indent -width PFIL_WAITOK -compact 127.It PFIL_IN 128call me on incoming packets 129.It PFIL_OUT 130call me on outgoing packets 131.It PFIL_ALL 132call me on all of the above 133.It PFIL_WAITOK 134OK to call malloc with M_WAITOK. 135.El 136.Pp 137The 138.Nm 139interface is enabled in the kernel via the 140.Sy PFIL_HOOKS 141option. 142.Sh SEE ALSO 143.Xr bpf 4 144.Sh HISTORY 145The 146.Nm 147interface first appeared in 148.Nx 1.3 . 149The 150.Nm 151input and output lists were originally implemented as 152.Aq Pa sys/queue.h 153.Dv LIST 154structures; 155however this was changed in 156.Nx 1.4 157to 158.Dv TAILQ 159structures. 160This change was to allow the input and output filters to be processed in 161reverse order, to allow the same path to be taken, in or out of the kernel. 162.Pp 163The 164.Nm 165interface was changed in 1.4T to accept a 3rd parameter to both 166.Fn pfil_add_hook 167and 168.Fn pfil_remove_hook , 169introducing the capability of per-protocol filtering. 170This was done primarily in order to support filtering of IPv6. 171.Pp 172In 1.5K, the 173.Nm 174framework was changed to work with an arbitrary number of filtering points, 175as well as be less IP-centric. 176.Pp 177The 178.Nm 179interface was imported from 180.Nx 181into 182.Dx 1.0 . 183.Sh AUTHORS 184The 185.Nm 186interface was designed and implemented by Matthew R. Green, with help 187from Darren Reed, Jason R. Thorpe and Charles M. Hannum. 188Darren Reed added support for IPv6 in addition to IPv4. 189Jason R. Thorpe added support for multiple hooks and other clean up. 190.Sh BUGS 191The current 192.Nm 193implementation will need changes to suit a threaded kernel model. 194