1 .\" $NetBSD: pfil.9,v 1.22 2003/07/01 13:04:06 wiz Exp $
3 .\" Copyright (c) 1996 Matthew R. Green
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36 .Nm pfil_head_register ,
37 .Nm pfil_head_unregister ,
40 .Nm pfil_add_hook_flags ,
41 .Nm pfil_remove_hook ,
42 .Nm pfil_remove_hook_flags ,
48 .Nd packet filter interface
55 typedef int (*pfil_func_t)(void *arg, struct mbuf **mp, struct ifnet *, int dir, struct inpcb);
57 typedef int (*pfil_func_flags_t)(void *arg, struct mbuf **mp, struct ifnet *, int dir, int flags, struct inpcb);
59 .Fn pfil_head_register "struct pfil_head *head"
61 .Fn pfil_head_unregister "struct pfil_head *head"
62 .Ft "struct pfil_head *"
63 .Fn pfil_head_get "int af" "u_long dlt"
65 .Fn pfil_add_hook "pfil_func_t" "void *arg" "struct pfil_head *"
67 .Fn pfil_add_hook_flags "pfil_func_flags_t" "void *arg" "int flags" "struct pfil_head *"
69 .Fn pfil_remove_hook "pfil_func_t" "void *arg" "struct pfil_head *"
71 .Fn pfil_remove_hook_flags "pfil_func_flags_t" "void *arg" "int flags" "struct pfil_head *"
73 .Fn pfil_run_hooks "struct pfil_head *head" "struct mbuf **mp" "struct ifnet *" "int dir" "int flags" "struct inpcb *"
75 .Fn pfil_rlock "struct pfil_head *" "struct rm_priotracker *"
77 .Fn pfil_runlock "struct pfil_head *" "struct rm_priotracker *"
79 .Fn pfil_wlock "struct pfil_head *"
81 .Fn pfil_wunlock "struct pfil_head *"
86 framework allows for a specified function to be invoked for every
87 incoming or outgoing packet for a particular network I/O stream.
88 These hooks may be used to implement a firewall or perform packet
91 Packet filtering points are registered with
92 .Fn pfil_head_register .
93 Filtering points are identified by a key
100 Packet filters use the key and data link type to look up the filtering
101 point with which they register themselves.
102 The key is unique to the filtering point.
103 The data link type is a
105 DLT constant indicating what kind of header is present on the packet
106 at the filtering point.
107 Each filtering point uses common per-VNET rmlock by default.
108 This can be changed by specifying
109 .Vt PFIL_FLAG_PRIVATE_LOCK
115 Note that specifying private lock can break filters sharing the same
116 ruleset and/or state between different data link types.
117 Filtering points may be unregistered with the
118 .Fn pfil_head_unregister
121 Packet filters register/unregister themselves with a filtering point
126 functions, respectively.
128 The head is looked up using the
130 function, which takes the key and data link type that the packet filter
132 Filters may provide an argument to be passed to the filter when
135 When a filter is invoked, the packet appears just as if it
136 .Dq came off the wire .
137 That is, all protocol fields are in network byte order.
138 The filter is called with its specified argument, the pointer to the
141 containing the packet, the pointer to the network
142 interface that the packet is traversing, and the direction
146 that the packet is traveling.
149 argument will indicate if an outgoing packet is simply being forwarded with the
151 The filter may change which mbuf the
154 The filter returns an error (errno) if the packet processing is to stop, or 0
155 if the processing is to continue.
156 If the packet processing is to stop, it is the responsibility of the
157 filter to free the packet.
159 Every filter hook is called with
162 All heads uses the same lock within the same VNET instance.
163 Packet filter can use this lock instead of own locking model to
173 .Va struct rm_priotracker
174 to be passed as argument.
175 Filter can acquire and release writer lock via
184 Currently, filtering points are implemented for the following link types:
186 .Bl -tag -width "AF_INET6" -offset XXX -compact
199 structure for the given key/dlt.
205 return 0 if successful.
209 is expected to always succeed.
212 .Fn pfil_head_unregister
222 interface first appeared in
226 input and output lists were originally implemented as
230 however this was changed in
235 This change was to allow the input and output filters to be processed in
236 reverse order, to allow the same path to be taken, in or out of the kernel.
240 interface was changed in 1.4T to accept a 3rd parameter to both
243 .Fn pfil_remove_hook ,
244 introducing the capability of per-protocol filtering.
245 This was done primarily in order to support filtering of IPv6.
249 framework was changed to work with an arbitrary number of filtering points,
250 as well as be less IP-centric.
252 Fine-grained locking was added in
255 lock export was added in
260 is being modified, no traffic is diverted
262 This means that traffic may be dropped unconditionally for a short period