1.\" $NetBSD: pfil.9,v 1.22 2003/07/01 13:04:06 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.\" $FreeBSD$ 30.Dd September 8, 2003 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 *head" 50.Ft int 51.Fn pfil_head_unregister "struct pfil_head *head" 52.Ft struct pfil_head * 53.Fn pfil_head_get "int af" "u_long dlt" 54.Ft struct packet_filter_hook * 55.Fn pfil_hook_get "int dir" "struct pfil_head *head" 56.Ft void 57.Fn pfil_add_hook "int (*func)()" "void *arg" "int flags" "struct pfil_head *" 58.Ft void 59.Fn pfil_remove_hook "int (*func)()" "void *arg" "int flags" "struct pfil_head *" 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 *head" "struct mbuf **mp" "struct ifnet *" "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 (PFIL_IN 108or PFIL_OUT) that the packet is traveling. 109The filter may change which mbuf the mbuf ** argument references. 110The filter returns an errno if the packet processing is to stop, or 0 111if 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.Nm 117interface is enabled in the kernel via the 118.Sy PFIL_HOOKS 119option. 120.Sh RETURN VALUES 121If successful, 122.Fn pfil_head_get 123returns the pfil_head structure for the given key/dlt. 124.Fn pfil_add_hook 125and 126.Fn pfil_remove_hook 127return 0 if successful. If called with flag PFIL_WAITOK, 128.Fn pfil_remove_hook 129is expected to always succeed. 130.Pp 131.Fn pfil_head_unregister 132might sleep! 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.Fd \*[Lt]sys/queue.h\*[Gt] 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 166Fine-grained locking was added in 167.Fx 5.2 . 168.Sh BUGS 169.Fn pfil_hook_get 170is only safe for internal use. 171.Pp 172FreeBSD implements only hooks for AF_INET and AF_INET6. 173Packets diverted through these hooks have data in 174host byte order contrary to the above statements. 175.Pp 176The 177.Xr bridge 4 178diverts inbound AF_INET traffic, but contrary to the above 179statements, the data is provided in host byte order. 180.Pp 181When a pfil_head is being modified no traffic is diverted 182(to avoid deadlock). 183This means that unwanted traffic may flow for a short period 184of time. 185.Sh SEE ALSO 186.Xr bpf 4 , 187.Xr bridge 4 188