pfil(9)
- NetBSD Manual Pages
PFIL(9) NetBSD Kernel Developer's Manual PFIL(9)
NAME
pfil, pfil_head_register, pfil_head_unregister, pfil_head_get,
pfil_hook_get, pfil_add_hook, pfil_remove_hook, pfil_run_hooks,
pfil_add_ihook, pfil_remove_ihook, pfil_run_addrhooks, pfil_run_ifhooks
-- packet filter interface
SYNOPSIS
#include <sys/param.h>
#include <sys/mbuf.h>
#include <net/if.h>
#include <net/pfil.h>
int
pfil_head_register(struct pfil_head *ph);
int
pfil_head_unregister(struct pfil_head *ph);
struct pfil_head *
pfil_head_get(int af, u_long dlt);
struct packet_filter_hook *
pfil_hook_get(int dir, struct pfil_head *ph);
int
pfil_add_hook(int (*func)(), void *arg, int flags, struct pfil_head *ph);
int
pfil_remove_hook(int (*func)(), void *arg, int flags,
struct pfil_head *ph);
int
(*func)(void *arg, struct mbuf **mp, struct ifnet *, int dir);
int
pfil_run_hooks(struct pfil_head *ph, struct mbuf **mp, struct ifnet *ifp,
int dir);
int
pfil_add_ihook(void (*ifunc)(), void *arg, int flags,
struct pfil_head *ph);
int
pfil_remove_ihook(void (*ifunc)(), void *arg, int flags,
struct pfil_head *ph);
void
(*ifunc)(void *arg, unsigned long cmd, void *ptr);
void
pfil_run_addrhooks(struct pfil_head *ph, unsigned long,
struct ifaddr *ifa);
void
pfil_run_ifhooks(struct pfil_head *ph, unsigned long, struct ifnet *ifp);
DESCRIPTION
The pfil 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 trans-
formations.
Packet filtering points are registered with pfil_head_register(). Fil-
tering points are identified by a key (void *) and a data link type (int)
in the 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_type constant indicating what kind of header is present on the packet
at the filtering point. Filtering points may be unregistered with the
pfil_head_unregister() function.
Packet filters register/unregister themselves with a filtering point with
the pfil_add_hook() and pfil_remove_hook() functions, respectively. The
head is looked up using the 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 mbuf containing the packet, the pointer to the network interface
that the packet is traversing, and the direction (either PFIL_IN or
PFIL_OUT, see also below) that the packet is traveling. The filter may
change which mbuf the mbuf ** argument references. The filter returns an
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.
The flags parameter, used in the pfil_add_hook() and pfil_remove_hook()
functions, indicates when the filter should be called. The flags are:
PFIL_IN call me on incoming packets
PFIL_OUT call me on outgoing packets
PFIL_ALL call me on all of the above
By the same token, event handlers register/unregister themselves with the
pfil_add_ihook() and pfil_remove_ihook() functions, respectively. The
event handler is called with its specified argument, the event id (either
PFIL_IFNET_ATTACH or PFIL_IFNET_DETACH, see also below) or ioctl number,
and the pointer to the network interface or the pointer to the ifaddr.
The flags parameter, used in the pfil_add_ihook() and pfil_remove_ihook()
functions, indicates when the filter should be called. The flags are:
PFIL_IFADDR call me on interface reconfig (cmd is ioctl #)
PFIL_IFNET call me on interface attach/detach (cmd is either
PFIL_IFNET_ATTACH or PFIL_IFNET_DETACH)
SEE ALSO
bpf(4)
HISTORY
The pfil interface first appeared in NetBSD 1.3. The pfil input and out-
put lists were originally implemented as <sys/queue.h> LIST structures;
however this was changed in NetBSD 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 pfil interface was changed in 1.4T to accept a 3rd parameter to both
pfil_add_hook() and pfil_remove_hook(), introducing the capability of
per-protocol filtering. This was done primarily in order to support fil-
tering of IPv6.
In 1.5K, the pfil framework was changed to work with an arbitrary number
of filtering points, as well as be less IP-centric.
pfil_add_ihook() and pfil_remove_ihook() were added in NetBSD 8.0.
AUTHORS
The pfil interface was designed and implemented by Matthew R. Green, with
help from Darren Reed, Jason R. Thorpe, and Charles M. Hannum. Darren
Reed added support for IPv6 in addition to IPv4. Jason R. Thorpe added
support for multiple hooks and other clean up.
BUGS
The current pfil implementation will need changes to suit a threaded ker-
nel model.
NetBSD 9.0 January 17, 2018 NetBSD 9.0
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