1.\" $NetBSD: pfil.9,v 1.24 2004/01/01 15:24:35 wiz Exp $ 2.\" $DragonFly: src/share/man/man9/pfil.9,v 1.9 2008/09/20 06:08:13 sephe 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 15, 2008 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_add_hook , 39.Nm pfil_remove_hook , 40.Nm pfil_run_hooks 41.Nd packet filter interface 42.Sh SYNOPSIS 43.In sys/param.h 44.In sys/mbuf.h 45.In net/if.h 46.In net/pfil.h 47.Ft typedef int 48.Fn (*pfil_func_t) "void *arg" "struct mbuf **mp" "struct ifnet *ifp" "int dir" 49.Ft int 50.Fn pfil_head_register "struct pfil_head *ph" 51.Ft int 52.Fn pfil_head_unregister "struct pfil_head *pfh" 53.Ft struct pfil_head * 54.Fn pfil_head_get "int type" "u_long val" 55.Ft void 56.Fn pfil_add_hook "pfil_func_t func" "void *arg" "int flags" "struct pfil_head *ph" 57.Ft void 58.Fn pfil_remove_hook "pfil_func_t func" "void *arg" "int flags" "struct pfil_head *ph" 59.Ft int 60.Fn pfil_run_hooks "struct pfil_head *ph" "struct mbuf **mp" "struct ifnet *ifp" "int dir" 61.Sh DESCRIPTION 62The 63.Nm 64framework allows for a specified function to be invoked for every 65incoming or outgoing packet for a particular network I/O stream. 66These hooks may be used to implement a firewall or perform packet 67transformations. 68.Pp 69Packet filtering points are registered with 70.Fn pfil_head_register . 71Filtering points are identified by a key (void *) and a data link type 72(int) in the 73.Em pfil_head 74structure. 75Packet filters use the key and data link type to look up the filtering 76point with which they register themselves. 77The key is unique to the filtering point. 78The data link type is a 79.Xr bpf 4 80DLT constant indicating what kind of header is present on the packet 81at the filtering point. 82Filtering points may be unregistered with the 83.Fn pfil_head_unregister 84function. 85.Pp 86Packet filters register/unregister themselves with a filtering point 87with the 88.Fn pfil_add_hook 89and 90.Fn pfil_remove_hook 91functions, respectively. 92The head is looked up using the 93.Fn pfil_head_get 94function, which takes the key and data link type that the packet filter 95expects. 96Filters may provide an argument to be passed to the filter when 97invoked on a packet. 98.Pp 99When a filter is invoked, the packet appears just as if it 100.Dq came off the wire . 101That is, all protocol fields are in network byte order. 102The filter is called with its specified argument, the pointer to the 103pointer to the mbuf containing the packet, the pointer to the network 104interface that the packet is traversing, and the direction 105.Dv ( PFIL_IN 106or 107.Dv PFIL_OUT , 108see also below) that the packet is traveling. 109The filter may change which mbuf the mbuf ** argument references. 110The filter returns an 111.Va errno 112if the packet processing is to stop, or 0 if the processing is to continue. 113If the packet processing is to stop, it is the responsibility of the 114filter to free the packet. 115.Pp 116The 117.Em flags 118parameter, used in the 119.Fn pfil_add_hook 120and 121.Fn pfil_remove_hook 122functions, indicates when the filter should be called. 123The flags are: 124.Bl -tag -offset indent -width ".Dv PFIL_MPSAFE" -compact 125.It Dv PFIL_IN 126call me on incoming packets 127.It Dv PFIL_OUT 128call me on outgoing packets 129.It Dv PFIL_ALL 130call me on all of the above 131.It Dv PFIL_MPSAFE 132call me without BGL 133.El 134.Sh SEE ALSO 135.Xr bpf 4 136.Sh HISTORY 137The 138.Nm 139interface first appeared in 140.Nx 1.3 . 141The 142.Nm 143input and output lists were originally implemented as 144.In sys/queue.h 145.Dv LIST 146structures; 147however this was changed in 148.Nx 1.4 149to 150.Dv TAILQ 151structures. 152This change was to allow the input and output filters to be processed in 153reverse order, to allow the same path to be taken, in or out of the kernel. 154.Pp 155The 156.Nm 157interface was changed in 1.4T to accept a 3rd parameter to both 158.Fn pfil_add_hook 159and 160.Fn pfil_remove_hook , 161introducing the capability of per-protocol filtering. 162This was done primarily in order to support filtering of IPv6. 163.Pp 164In 1.5K, the 165.Nm 166framework was changed to work with an arbitrary number of filtering points, 167as well as be less IP-centric. 168.Pp 169The 170.Nm 171interface was imported from 172.Nx 173into 174.Dx 1.0 175and was reworked to suit a threaded kernel model in 176.Dx 2.1 . 177.Sh AUTHORS 178The 179.Nm 180interface was designed and implemented by Matthew R. Green, with help 181from Darren Reed, Jason R. Thorpe and Charles M. Hannum. 182Darren Reed added support for IPv6 in addition to IPv4. 183Jason R. Thorpe added support for multiple hooks and other clean up. 184