pfil.9freebsd

Langue: en

Version: 309274 (debian - 07/07/09)

Section: 9 (Appels noyau Linux)


BSD mandoc

NAME

pfil pfil_head_register pfil_head_unregister pfil_head_get pfil_hook_get pfil_add_hook pfil_remove_hook pfil_run_hooks - packet filter interface

SYNOPSIS

In sys/param.h In sys/mbuf.h In net/if.h In net/pfil.h Ft int Fn pfil_head_register struct pfil_head *head Ft int Fn pfil_head_unregister struct pfil_head *head Ft struct pfil_head * Fn pfil_head_get int af u_long dlt Ft struct packet_filter_hook * Fn pfil_hook_get int dir struct pfil_head *head Ft void Fn pfil_add_hook int (*func)() void *arg int flags struct pfil_head * Ft void Fn pfil_remove_hook int (*func)() void *arg int flags struct pfil_head * Ft int Fn (*func) void *arg struct mbuf **mp struct ifnet * int dir struct inpcb * Ft int Fn pfil_run_hooks struct pfil_head *head struct mbuf **mp struct ifnet * int dir struct inpcb *

DESCRIPTION

The framework allows for a specified function to be invoked for every incoming or outgoing packet for a particular network I/O stream. These hooks may be used to implement a firewall or perform packet transformations.

Packet filtering points are registered with Fn pfil_head_register . Filtering points are identified by a key (Vt void * ) and a data link type (Vt int ) in the Vt pfil_head structure. Packet filters use the key and data link type to look up the filtering point with which they register themselves. The key is unique to the filtering point. The data link type is a bpf(4) DLT constant indicating what kind of header is present on the packet at the filtering point. Filtering points may be unregistered with the Fn pfil_head_unregister function.

Packet filters register/unregister themselves with a filtering point with the Fn pfil_add_hook and Fn pfil_remove_hook functions, respectively. The head is looked up using the Fn pfil_head_get function, which takes the key and data link type that the packet filter expects. Filters may provide an argument to be passed to the filter when invoked on a packet.

When a filter is invoked, the packet appears just as if it ``came off the wire'' That is, all protocol fields are in network byte order. The filter is called with its specified argument, the pointer to the pointer to the Vt mbuf containing the packet, the pointer to the network interface that the packet is traversing, and the direction ( PFIL_IN or PFIL_OUT that the packet is traveling. The filter may change which mbuf the Vt mbuf ** argument references. The filter returns an error (errno) if the packet processing is to stop, or 0 if the processing is to continue. If the packet processing is to stop, it is the responsibility of the filter to free the packet.

RETURN VALUES

If successful, Fn pfil_head_get returns the Vt pfil_head structure for the given key/dlt. The Fn pfil_add_hook and Fn pfil_remove_hook functions return 0 if successful. If called with flag PFIL_WAITOK Fn pfil_remove_hook is expected to always succeed.

The Fn pfil_head_unregister function might sleep!

SEE ALSO

bpf(4), if_bridge4

HISTORY

The interface first appeared in Nx 1.3 . The input and output lists were originally implemented as In sys/queue.h LIST structures; however this was changed in Nx 1.4 to TAILQ structures. This change was to allow the input and output filters to be processed in reverse order, to allow the same path to be taken, in or out of the kernel.

The interface was changed in 1.4T to accept a 3rd parameter to both Fn pfil_add_hook and Fn pfil_remove_hook , introducing the capability of per-protocol filtering. This was done primarily in order to support filtering of IPv6.

In 1.5K, the framework was changed to work with an arbitrary number of filtering points, as well as be less IP-centric.

Fine-grained locking was added in Fx 5.2 .

BUGS

The Fn pfil_hook_get function is only safe for internal use.

Fx implements only hooks for AF_INET and AF_INET6 Packets diverted through these hooks have data in host byte order contrary to the above statements.

The if_bridge4 diverts AF_INET and AF_INET6 traffic according to its sysctl settings, but contrary to the above statements, the data is provided in host byte order.

When a Vt pfil_head is being modified, no traffic is diverted (to avoid deadlock). This means that traffic may be dropped unconditionally for a short period of time. Fn pfil_run_hooks will return Er ENOBUFS to indicate this.