pfil(9) - NetBSD Manual Pages

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PFIL(9)                NetBSD Kernel Developer's Manual                PFIL(9)


NAME

     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 -- packet filter
     interface


SYNOPSIS

     #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);


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 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:

           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 10.99                   January 15, 2022                   NetBSD 10.99