NAME

     ng_bpf — Berkeley packet filter netgraph node type

SYNOPSIS

     #include <sys/types.h>
     #include <net/bpf.h>
     #include <netgraph.h>
     #include <netgraph/ng_bpf.h>

DESCRIPTION

     The bpf node type allows Berkeley Packet Filter (see bpf(4)) filters to be applied to data travelling
     through a Netgraph network.  Each node allows an arbitrary number of connections to arbitrarily named
     hooks.  With each hook is associated a bpf(4) filter program which is applied to incoming data only, a
     destination hook for matching packets, a destination hook for non-matching packets, and various statistics
     counters.

     A bpf(4) program returns an unsigned integer, which is normally interpreted as the length of the prefix of
     the packet to return.  In the context of this node type, returning zero is considered a non-match, in which
     case the entire packet is delivered out the non-match destination hook.  Returning a value greater than
     zero causes the packet to be truncated to that length and delivered out the match destination hook.  Either
     or both destination hooks may be the empty string, or may not exist, in which case the packet is dropped.

     New hooks are initially configured to drop all packets.  A new filter program may be installed using the
     NGM_BPF_SET_PROGRAM control message.

HOOKS

     This node type supports any number of hooks having arbitrary names.

CONTROL MESSAGES

     This node type supports the generic control messages, plus the following:

     NGM_BPF_SET_PROGRAM (setprogram)
          This command sets the filter program that will be applied to incoming data on a hook.  The following
          structure must be supplied as an argument:

              struct ng_bpf_hookprog {
                char            thisHook[NG_HOOKSIZ];     /* name of hook */
                char            ifMatch[NG_HOOKSIZ];      /* match dest hook */
                char            ifNotMatch[NG_HOOKSIZ];   /* !match dest hook */
                int32_t         bpf_prog_len;             /* #insns in program */
                struct bpf_insn bpf_prog[];               /* bpf program */
              };

          The hook to be updated is specified in thisHook.  The BPF program is the sequence of instructions in
          the bpf_prog array; there must be bpf_prog_len of them.  Matching and non-matching incoming packets
          are delivered out the hooks named ifMatch and ifNotMatch, respectively.  The program must be a valid
          bpf(4) program or else EINVAL is returned.

     NGM_BPF_GET_PROGRAM (getprogram)
          This command takes an ASCII string argument, the hook name, and returns the corresponding struct
          ng_bpf_hookprog as shown above.

     NGM_BPF_GET_STATS (getstats)
          This command takes an ASCII string argument, the hook name, and returns the statistics associated with
          the hook as a struct ng_bpf_hookstat.

     NGM_BPF_CLR_STATS (clrstats)
          This command takes an ASCII string argument, the hook name, and clears the statistics associated with
          the hook.

     NGM_BPF_GETCLR_STATS (getclrstats)
          This command is identical to NGM_BPF_GET_STATS, except that the statistics are also atomically
          cleared.

SHUTDOWN

     This node shuts down upon receipt of a NGM_SHUTDOWN control message, or when all hooks have been
     disconnected.

EXAMPLES

     It is possible to configure a node from the command line, using tcpdump(1) to generate raw BPF instructions
     which are then fed into an awk(1) script to create the ASCII form of a NGM_BPF_SET_PROGRAM control message,
     as demonstrated here:

         #!/bin/sh

         PATTERN="tcp dst port 80"
         NODEPATH="my_node:"
         INHOOK="hook1"
         MATCHHOOK="hook2"
         NOTMATCHHOOK="hook3"

         BPFPROG=$( tcpdump -s 8192 -p -ddd ${PATTERN} | \
                    ( read len ; \
                      echo -n "bpf_prog_len=$len" ; \
                      echo -n "bpf_prog=[" ; \
                      while read code jt jf k ; do \
                          echo -n " { code=$code jt=$jt jf=$jf k=$k }" ; \
                      done ; \
                      echo " ]" ) )

         ngctl msg ${NODEPATH} setprogram { thisHook=\"${INHOOK}\" \
           ifMatch=\"${MATCHHOOK}\" \
           ifNotMatch=\"${NOTMATCHHOOK}\" \
           ${BPFPROG} }

SEE ALSO

     bpf(4), netgraph(4), ngctl(8)

HISTORY

     The ng_bpf node type was implemented in FreeBSD 4.0.

AUTHORS

     Archie Cobbs <archie@FreeBSD.org>

BUGS

     When built as a loadable kernel module, this module includes the file net/bpf_filter.c.  Although loading
     the module should fail if net/bpf_filter.c already exists in the kernel, currently it does not, and the
     duplicate copies of the file do not interfere.  However, this may change in the future.