PFIL(9) | Kernel Developer's Manual | PFIL(9) |
pfil
, pfil_head_create
,
pfil_head_destroy
,
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
—
#include <sys/param.h>
#include <sys/mbuf.h>
#include <net/if.h>
#include <net/pfil.h>
pfil_head_t *
pfil_head_create
(int
type, void
*key);
int
pfil_head_destroy
(pfil_head_t
*ph);
pfil_head_t *
pfil_head_get
(int
type, void
*key);
struct packet_filter_hook *
pfil_hook_get
(int
dir, pfil_head_t
*ph);
int
pfil_add_hook
(pfil_func_t
func, void *arg,
int flags,
pfil_head_t *ph);
int
pfil_remove_hook
(pfil_func_t
func, void *arg,
int flags,
pfil_head_t *ph);
int
(*func)
(void
*arg, struct mbuf
**mp, struct ifnet
*, int dir);
int
pfil_run_hooks
(pfil_head_t
*ph, struct mbuf
**mp, struct ifnet
*ifp, int dir);
int
pfil_add_ihook
(pfil_ifunc_t
ifunc, void *arg,
int flags,
pfil_head_t *ph);
int
pfil_remove_ihook
(pfil_ifunc_t
ifunc, void *arg,
int flags,
pfil_head_t *ph);
void
(*ifunc)
(void
*arg, unsigned long
cmd, void
*ptr);
void
pfil_run_addrhooks
(pfil_head_t
*ph, unsigned long,
struct ifaddr *ifa);
void
pfil_run_ifhooks
(pfil_head_t
*ph, unsigned long,
struct ifnet *ifp);
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
transformations.
Packet filtering points are created with
pfil_head_create
(). Filtering points are identified
by a data link (int) type and a
(void *) key. If a packet
filtering point already exists for that data link type
and key then the
pfil_head_create
() function returns
NULL
. Packet filters use the
pfil_head_get
() function specifying the data link
type and the key 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 destroyed with the
pfil_head_destroy
() 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 data link type and the
key 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:
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
PFIL_IFNET
PFIL_IFNET_ATTACH
or
PFIL_IFNET_DETACH
)pfil
interface first appeared in
NetBSD 1.3. The pfil
input and
output 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
filtering 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.
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.
pfil
implementation will need changes to
suit a threaded kernel model.
January 15, 2022 | NetBSD 10.0 |