NG_BPF(4) | Device Drivers Manual | NG_BPF(4) |
NAME¶
ng_bpf — Berkeley packet filter netgraph node typeSYNOPSIS¶
#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 theNGM_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
- 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; /* #isns in program */ struct bpf_insn bpf_prog[]; /* bpf program */ };
thisHook
. The BPF program is the sequence of instructions in thebpf_prog
array; there must bebpf_prog_len
of them. Matching and non-matching incoming packets are delivered out the hooks namedifMatch
andifNotMatch
, respectively. The program must be a valid bpf(4) program or elseEINVAL
is returned. NGM_BPF_GET_PROGRAM
- 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
- 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
- This command takes an ASCII string argument, the hook name, and clears the statistics associated with the hook.
NGM_BPF_GETCLR_STATS
- 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 aNGM_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 aNGM_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 -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.May 30, 2007 | Debian |