Patchwork [2/2] netfilter: add xt_bpf xtables match

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Submitter Willem de Bruijn
Date Dec. 5, 2012, 7:22 p.m.
Message ID <1354735339-13402-3-git-send-email-willemb@google.com>
Download mbox | patch
Permalink /patch/203929/
State Superseded
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Comments

Willem de Bruijn - Dec. 5, 2012, 7:22 p.m.
A new match that executes sk_run_filter on every packet. BPF filters
can access skbuff fields that are out of scope for existing iptables
rules, allow more expressive logic, and on platforms with JIT support
can even be faster.

I have a corresponding iptables patch that takes `tcpdump -ddd`
output, as used in the examples below. The two parts communicate
using a variable length structure. This is similar to ebt_among,
but new for iptables.

Verified functionality by inserting an ip source filter on chain
INPUT and an ip dest filter on chain OUTPUT and noting that ping
failed while a rule was active:

iptables -v -A INPUT -m bpf --bytecode '4,32 0 0 12,21 0 1 $SADDR,6 0 0 96,6 0 0 0,' -j DROP
iptables -v -A OUTPUT -m bpf --bytecode '4,32 0 0 16,21 0 1 $DADDR,6 0 0 96,6 0 0 0,' -j DROP

Evaluated throughput by running netperf TCP_STREAM over loopback on
x86_64. I expected the BPF filter to outperform hardcoded iptables
filters when replacing multiple matches with a single bpf match, but
even a single comparison to u32 appears to do better. Relative to the
benchmark with no filter applied, rate with 100 BPF filters dropped
to 81%. With 100 U32 filters it dropped to 55%. The difference sounds
excessive to me, but was consistent on my hardware. Commands used:

for i in `seq 100`; do iptables -A OUTPUT -m bpf --bytecode '4,48 0 0 9,21 0 1 20,6 0 0 96,6 0 0 0,' -j DROP; done
for i in `seq 3`; do netperf -t TCP_STREAM -I 99 -H localhost; done

iptables -F OUTPUT

for i in `seq 100`; do iptables -A OUTPUT -m u32 --u32 '6&0xFF=0x20' -j DROP; done
for i in `seq 3`; do netperf -t TCP_STREAM -I 99 -H localhost; done

FYI: perf top

[bpf]
    33.94%  [kernel]          [k] copy_user_generic_string
     8.92%  [kernel]          [k] sk_run_filter
     7.77%  [ip_tables]       [k] ipt_do_table

[u32]
    22.63%  [kernel]          [k] copy_user_generic_string
    14.46%  [kernel]          [k] memcpy
     9.19%  [ip_tables]       [k] ipt_do_table
     8.47%  [xt_u32]          [k] u32_mt
     5.32%  [kernel]          [k] skb_copy_bits

The big difference appears to be in memory copying. I have not
looked into u32, so cannot explain this right now. More interestingly,
at higher rate, sk_run_filter appears to use as many cycles as u32_mt
(both traces have roughly the same number of events).

One caveat: to work independent of device link layer, the filter
expects DLT_RAW style BPF programs, i.e., those that expect the
packet to start at the IP layer.
---
 include/linux/netfilter/xt_bpf.h |   17 +++++++
 net/netfilter/Kconfig            |    9 ++++
 net/netfilter/Makefile           |    1 +
 net/netfilter/x_tables.c         |    5 +-
 net/netfilter/xt_bpf.c           |   88 ++++++++++++++++++++++++++++++++++++++
 5 files changed, 118 insertions(+), 2 deletions(-)
 create mode 100644 include/linux/netfilter/xt_bpf.h
 create mode 100644 net/netfilter/xt_bpf.c
Pablo Neira - Dec. 5, 2012, 7:48 p.m.
Hi Willem,

On Wed, Dec 05, 2012 at 02:22:19PM -0500, Willem de Bruijn wrote:
> A new match that executes sk_run_filter on every packet. BPF filters
> can access skbuff fields that are out of scope for existing iptables
> rules, allow more expressive logic, and on platforms with JIT support
> can even be faster.
> 
> I have a corresponding iptables patch that takes `tcpdump -ddd`
> output, as used in the examples below. The two parts communicate
> using a variable length structure. This is similar to ebt_among,
> but new for iptables.
> 
> Verified functionality by inserting an ip source filter on chain
> INPUT and an ip dest filter on chain OUTPUT and noting that ping
> failed while a rule was active:
> 
> iptables -v -A INPUT -m bpf --bytecode '4,32 0 0 12,21 0 1 $SADDR,6 0 0 96,6 0 0 0,' -j DROP
> iptables -v -A OUTPUT -m bpf --bytecode '4,32 0 0 16,21 0 1 $DADDR,6 0 0 96,6 0 0 0,' -j DROP

I like this BPF idea for iptables.

I made a similar extension time ago, but it was taking a file as
parameter. That file contained in BPF code. I made a simple bison
parser that takes BPF code and put it into the bpf array of
instructions. It would be a bit more intuitive to define a filter and
we can distribute it with iptables.

Let me check on my internal trees, I can put that user-space code
somewhere in case you're interested.

> Evaluated throughput by running netperf TCP_STREAM over loopback on
> x86_64. I expected the BPF filter to outperform hardcoded iptables
> filters when replacing multiple matches with a single bpf match, but
> even a single comparison to u32 appears to do better. Relative to the
> benchmark with no filter applied, rate with 100 BPF filters dropped
> to 81%. With 100 U32 filters it dropped to 55%. The difference sounds
> excessive to me, but was consistent on my hardware. Commands used:
> 
> for i in `seq 100`; do iptables -A OUTPUT -m bpf --bytecode '4,48 0 0 9,21 0 1 20,6 0 0 96,6 0 0 0,' -j DROP; done
> for i in `seq 3`; do netperf -t TCP_STREAM -I 99 -H localhost; done
> 
> iptables -F OUTPUT
> 
> for i in `seq 100`; do iptables -A OUTPUT -m u32 --u32 '6&0xFF=0x20' -j DROP; done
> for i in `seq 3`; do netperf -t TCP_STREAM -I 99 -H localhost; done
> 
> FYI: perf top
> 
> [bpf]
>     33.94%  [kernel]          [k] copy_user_generic_string
>      8.92%  [kernel]          [k] sk_run_filter
>      7.77%  [ip_tables]       [k] ipt_do_table
> 
> [u32]
>     22.63%  [kernel]          [k] copy_user_generic_string
>     14.46%  [kernel]          [k] memcpy
>      9.19%  [ip_tables]       [k] ipt_do_table
>      8.47%  [xt_u32]          [k] u32_mt
>      5.32%  [kernel]          [k] skb_copy_bits
> 
> The big difference appears to be in memory copying. I have not
> looked into u32, so cannot explain this right now. More interestingly,
> at higher rate, sk_run_filter appears to use as many cycles as u32_mt
> (both traces have roughly the same number of events).
> 
> One caveat: to work independent of device link layer, the filter
> expects DLT_RAW style BPF programs, i.e., those that expect the
> packet to start at the IP layer.
> ---
>  include/linux/netfilter/xt_bpf.h |   17 +++++++
>  net/netfilter/Kconfig            |    9 ++++
>  net/netfilter/Makefile           |    1 +
>  net/netfilter/x_tables.c         |    5 +-
>  net/netfilter/xt_bpf.c           |   88 ++++++++++++++++++++++++++++++++++++++
>  5 files changed, 118 insertions(+), 2 deletions(-)
>  create mode 100644 include/linux/netfilter/xt_bpf.h
>  create mode 100644 net/netfilter/xt_bpf.c
> 
> diff --git a/include/linux/netfilter/xt_bpf.h b/include/linux/netfilter/xt_bpf.h
> new file mode 100644
> index 0000000..23502c0
> --- /dev/null
> +++ b/include/linux/netfilter/xt_bpf.h
> @@ -0,0 +1,17 @@
> +#ifndef _XT_BPF_H
> +#define _XT_BPF_H
> +
> +#include <linux/filter.h>
> +#include <linux/types.h>
> +
> +struct xt_bpf_info {
> +	__u16 bpf_program_num_elem;
> +
> +	/* only used in kernel */
> +	struct sk_filter *filter __attribute__((aligned(8)));
> +
> +	/* variable size, based on program_num_elem */
> +	struct sock_filter bpf_program[0];
> +};
> +
> +#endif /*_XT_BPF_H */
> diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
> index c9739c6..c7cc0b8 100644
> --- a/net/netfilter/Kconfig
> +++ b/net/netfilter/Kconfig
> @@ -798,6 +798,15 @@ config NETFILTER_XT_MATCH_ADDRTYPE
>  	  If you want to compile it as a module, say M here and read
>  	  <file:Documentation/kbuild/modules.txt>.  If unsure, say `N'.
>  
> +config NETFILTER_XT_MATCH_BPF
> +	tristate '"bpf" match support'
> +	depends on NETFILTER_ADVANCED
> +	help
> +	  BPF matching applies a linux socket filter to each packet and
> +          accepts those for which the filter returns non-zero.
> +
> +	  To compile it as a module, choose M here.  If unsure, say N.
> +
>  config NETFILTER_XT_MATCH_CLUSTER
>  	tristate '"cluster" match support'
>  	depends on NF_CONNTRACK
> diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
> index 8e5602f..9f12eeb 100644
> --- a/net/netfilter/Makefile
> +++ b/net/netfilter/Makefile
> @@ -98,6 +98,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_IDLETIMER) += xt_IDLETIMER.o
>  
>  # matches
>  obj-$(CONFIG_NETFILTER_XT_MATCH_ADDRTYPE) += xt_addrtype.o
> +obj-$(CONFIG_NETFILTER_XT_MATCH_BPF) += xt_bpf.o
>  obj-$(CONFIG_NETFILTER_XT_MATCH_CLUSTER) += xt_cluster.o
>  obj-$(CONFIG_NETFILTER_XT_MATCH_COMMENT) += xt_comment.o
>  obj-$(CONFIG_NETFILTER_XT_MATCH_CONNBYTES) += xt_connbytes.o
> diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
> index 8d987c3..26306be 100644
> --- a/net/netfilter/x_tables.c
> +++ b/net/netfilter/x_tables.c
> @@ -379,8 +379,9 @@ int xt_check_match(struct xt_mtchk_param *par,
>  	if (XT_ALIGN(par->match->matchsize) != size &&
>  	    par->match->matchsize != -1) {
>  		/*
> -		 * ebt_among is exempt from centralized matchsize checking
> -		 * because it uses a dynamic-size data set.
> +		 * matches of variable size length, such as ebt_among,
> +		 * are exempt from centralized matchsize checking. They
> +		 * skip the test by setting xt_match.matchsize to -1.
>  		 */
>  		pr_err("%s_tables: %s.%u match: invalid size "
>  		       "%u (kernel) != (user) %u\n",
> diff --git a/net/netfilter/xt_bpf.c b/net/netfilter/xt_bpf.c
> new file mode 100644
> index 0000000..07077c5
> --- /dev/null
> +++ b/net/netfilter/xt_bpf.c
> @@ -0,0 +1,88 @@
> +/* Xtables module to match packets using a BPF filter.
> + * Copyright 2012 Google Inc.
> + * Written by Willem de Bruijn <willemb@google.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/skbuff.h>
> +#include <linux/ipv6.h>
> +#include <linux/filter.h>
> +#include <net/ip.h>
> +
> +#include <linux/netfilter/xt_bpf.h>
> +#include <linux/netfilter/x_tables.h>
> +
> +MODULE_AUTHOR("Willem de Bruijn <willemb@google.com>");
> +MODULE_DESCRIPTION("Xtables: BPF filter match");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("ipt_bpf");
> +MODULE_ALIAS("ip6t_bpf");
> +
> +static int bpf_mt_check(const struct xt_mtchk_param *par)
> +{
> +	struct xt_bpf_info *info = par->matchinfo;
> +	const struct xt_entry_match *match;
> +	struct sock_fprog program;
> +	int expected_len;
> +
> +	match = container_of(par->matchinfo, const struct xt_entry_match, data);
> +	expected_len = sizeof(struct xt_entry_match) +
> +		       sizeof(struct xt_bpf_info) +
> +		       (sizeof(struct sock_filter) *
> +			info->bpf_program_num_elem);
> +
> +	if (match->u.match_size != expected_len) {
> +		pr_info("bpf: check failed: incorrect length\n");
> +		return -EINVAL;
> +	}
> +
> +	program.len = info->bpf_program_num_elem;
> +	program.filter = info->bpf_program;
> +	if (sk_unattached_filter_create(&info->filter, &program)) {
> +		pr_info("bpf: check failed: parse error\n");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static bool bpf_mt(const struct sk_buff *skb, struct xt_action_param *par)
> +{
> +	const struct xt_bpf_info *info = par->matchinfo;
> +
> +	return SK_RUN_FILTER(info->filter, skb);
> +}
> +
> +static void bpf_mt_destroy(const struct xt_mtdtor_param *par)
> +{
> +	const struct xt_bpf_info *info = par->matchinfo;
> +	sk_unattached_filter_destroy(info->filter);
> +}
> +
> +static struct xt_match bpf_mt_reg __read_mostly = {
> +	.name		= "bpf",
> +	.revision	= 0,
> +	.family		= NFPROTO_UNSPEC,
> +	.checkentry	= bpf_mt_check,
> +	.match		= bpf_mt,
> +	.destroy	= bpf_mt_destroy,
> +	.matchsize	= -1, /* skip xt_check_match because of dynamic len */
> +	.me		= THIS_MODULE,
> +};
> +
> +static int __init bpf_mt_init(void)
> +{
> +	return xt_register_match(&bpf_mt_reg);
> +}
> +
> +static void __exit bpf_mt_exit(void)
> +{
> +	xt_unregister_match(&bpf_mt_reg);
> +}
> +
> +module_init(bpf_mt_init);
> +module_exit(bpf_mt_exit);
> -- 
> 1.7.7.3
> 
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Willem de Bruijn - Dec. 5, 2012, 8:10 p.m.
On Wed, Dec 5, 2012 at 2:48 PM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> Hi Willem,
>
> On Wed, Dec 05, 2012 at 02:22:19PM -0500, Willem de Bruijn wrote:
>> A new match that executes sk_run_filter on every packet. BPF filters
>> can access skbuff fields that are out of scope for existing iptables
>> rules, allow more expressive logic, and on platforms with JIT support
>> can even be faster.
>>
>> I have a corresponding iptables patch that takes `tcpdump -ddd`
>> output, as used in the examples below. The two parts communicate
>> using a variable length structure. This is similar to ebt_among,
>> but new for iptables.
>>
>> Verified functionality by inserting an ip source filter on chain
>> INPUT and an ip dest filter on chain OUTPUT and noting that ping
>> failed while a rule was active:
>>
>> iptables -v -A INPUT -m bpf --bytecode '4,32 0 0 12,21 0 1 $SADDR,6 0 0 96,6 0 0 0,' -j DROP
>> iptables -v -A OUTPUT -m bpf --bytecode '4,32 0 0 16,21 0 1 $DADDR,6 0 0 96,6 0 0 0,' -j DROP
>
> I like this BPF idea for iptables.
>
> I made a similar extension time ago, but it was taking a file as
> parameter. That file contained in BPF code. I made a simple bison
> parser that takes BPF code and put it into the bpf array of
> instructions. It would be a bit more intuitive to define a filter and
> we can distribute it with iptables.

That's cleaner, indeed. I actually like how tcpdump operates as a
code generator if you pass -ddd. Unfortunately, it generates code only
for link layer types of its supported devices, such as DLT_EN10MB and
DLT_LINUX_SLL. The network layer interface of basic iptables
(forgetting device dependent mechanisms as used in xt_mac) is DLT_RAW,
but that is rarely supported.

> Let me check on my internal trees, I can put that user-space code
> somewhere in case you're interested.

Absolutely. I'll be happy to revise to get it in. I'm also considering
sending a patch to tcpdump to make it generate code independent of the
installed hardware when specifying -y.

>> Evaluated throughput by running netperf TCP_STREAM over loopback on
>> x86_64. I expected the BPF filter to outperform hardcoded iptables
>> filters when replacing multiple matches with a single bpf match, but
>> even a single comparison to u32 appears to do better. Relative to the
>> benchmark with no filter applied, rate with 100 BPF filters dropped
>> to 81%. With 100 U32 filters it dropped to 55%. The difference sounds
>> excessive to me, but was consistent on my hardware. Commands used:
>>
>> for i in `seq 100`; do iptables -A OUTPUT -m bpf --bytecode '4,48 0 0 9,21 0 1 20,6 0 0 96,6 0 0 0,' -j DROP; done
>> for i in `seq 3`; do netperf -t TCP_STREAM -I 99 -H localhost; done
>>
>> iptables -F OUTPUT
>>
>> for i in `seq 100`; do iptables -A OUTPUT -m u32 --u32 '6&0xFF=0x20' -j DROP; done
>> for i in `seq 3`; do netperf -t TCP_STREAM -I 99 -H localhost; done
>>
>> FYI: perf top
>>
>> [bpf]
>>     33.94%  [kernel]          [k] copy_user_generic_string
>>      8.92%  [kernel]          [k] sk_run_filter
>>      7.77%  [ip_tables]       [k] ipt_do_table
>>
>> [u32]
>>     22.63%  [kernel]          [k] copy_user_generic_string
>>     14.46%  [kernel]          [k] memcpy
>>      9.19%  [ip_tables]       [k] ipt_do_table
>>      8.47%  [xt_u32]          [k] u32_mt
>>      5.32%  [kernel]          [k] skb_copy_bits
>>
>> The big difference appears to be in memory copying. I have not
>> looked into u32, so cannot explain this right now. More interestingly,
>> at higher rate, sk_run_filter appears to use as many cycles as u32_mt
>> (both traces have roughly the same number of events).
>>
>> One caveat: to work independent of device link layer, the filter
>> expects DLT_RAW style BPF programs, i.e., those that expect the
>> packet to start at the IP layer.
>> ---
>>  include/linux/netfilter/xt_bpf.h |   17 +++++++
>>  net/netfilter/Kconfig            |    9 ++++
>>  net/netfilter/Makefile           |    1 +
>>  net/netfilter/x_tables.c         |    5 +-
>>  net/netfilter/xt_bpf.c           |   88 ++++++++++++++++++++++++++++++++++++++
>>  5 files changed, 118 insertions(+), 2 deletions(-)
>>  create mode 100644 include/linux/netfilter/xt_bpf.h
>>  create mode 100644 net/netfilter/xt_bpf.c
>>
>> diff --git a/include/linux/netfilter/xt_bpf.h b/include/linux/netfilter/xt_bpf.h
>> new file mode 100644
>> index 0000000..23502c0
>> --- /dev/null
>> +++ b/include/linux/netfilter/xt_bpf.h
>> @@ -0,0 +1,17 @@
>> +#ifndef _XT_BPF_H
>> +#define _XT_BPF_H
>> +
>> +#include <linux/filter.h>
>> +#include <linux/types.h>
>> +
>> +struct xt_bpf_info {
>> +     __u16 bpf_program_num_elem;
>> +
>> +     /* only used in kernel */
>> +     struct sk_filter *filter __attribute__((aligned(8)));
>> +
>> +     /* variable size, based on program_num_elem */
>> +     struct sock_filter bpf_program[0];
>> +};
>> +
>> +#endif /*_XT_BPF_H */
>> diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
>> index c9739c6..c7cc0b8 100644
>> --- a/net/netfilter/Kconfig
>> +++ b/net/netfilter/Kconfig
>> @@ -798,6 +798,15 @@ config NETFILTER_XT_MATCH_ADDRTYPE
>>         If you want to compile it as a module, say M here and read
>>         <file:Documentation/kbuild/modules.txt>.  If unsure, say `N'.
>>
>> +config NETFILTER_XT_MATCH_BPF
>> +     tristate '"bpf" match support'
>> +     depends on NETFILTER_ADVANCED
>> +     help
>> +       BPF matching applies a linux socket filter to each packet and
>> +          accepts those for which the filter returns non-zero.
>> +
>> +       To compile it as a module, choose M here.  If unsure, say N.
>> +
>>  config NETFILTER_XT_MATCH_CLUSTER
>>       tristate '"cluster" match support'
>>       depends on NF_CONNTRACK
>> diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
>> index 8e5602f..9f12eeb 100644
>> --- a/net/netfilter/Makefile
>> +++ b/net/netfilter/Makefile
>> @@ -98,6 +98,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_IDLETIMER) += xt_IDLETIMER.o
>>
>>  # matches
>>  obj-$(CONFIG_NETFILTER_XT_MATCH_ADDRTYPE) += xt_addrtype.o
>> +obj-$(CONFIG_NETFILTER_XT_MATCH_BPF) += xt_bpf.o
>>  obj-$(CONFIG_NETFILTER_XT_MATCH_CLUSTER) += xt_cluster.o
>>  obj-$(CONFIG_NETFILTER_XT_MATCH_COMMENT) += xt_comment.o
>>  obj-$(CONFIG_NETFILTER_XT_MATCH_CONNBYTES) += xt_connbytes.o
>> diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
>> index 8d987c3..26306be 100644
>> --- a/net/netfilter/x_tables.c
>> +++ b/net/netfilter/x_tables.c
>> @@ -379,8 +379,9 @@ int xt_check_match(struct xt_mtchk_param *par,
>>       if (XT_ALIGN(par->match->matchsize) != size &&
>>           par->match->matchsize != -1) {
>>               /*
>> -              * ebt_among is exempt from centralized matchsize checking
>> -              * because it uses a dynamic-size data set.
>> +              * matches of variable size length, such as ebt_among,
>> +              * are exempt from centralized matchsize checking. They
>> +              * skip the test by setting xt_match.matchsize to -1.
>>                */
>>               pr_err("%s_tables: %s.%u match: invalid size "
>>                      "%u (kernel) != (user) %u\n",
>> diff --git a/net/netfilter/xt_bpf.c b/net/netfilter/xt_bpf.c
>> new file mode 100644
>> index 0000000..07077c5
>> --- /dev/null
>> +++ b/net/netfilter/xt_bpf.c
>> @@ -0,0 +1,88 @@
>> +/* Xtables module to match packets using a BPF filter.
>> + * Copyright 2012 Google Inc.
>> + * Written by Willem de Bruijn <willemb@google.com>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + */
>> +
>> +#include <linux/module.h>
>> +#include <linux/skbuff.h>
>> +#include <linux/ipv6.h>
>> +#include <linux/filter.h>
>> +#include <net/ip.h>
>> +
>> +#include <linux/netfilter/xt_bpf.h>
>> +#include <linux/netfilter/x_tables.h>
>> +
>> +MODULE_AUTHOR("Willem de Bruijn <willemb@google.com>");
>> +MODULE_DESCRIPTION("Xtables: BPF filter match");
>> +MODULE_LICENSE("GPL");
>> +MODULE_ALIAS("ipt_bpf");
>> +MODULE_ALIAS("ip6t_bpf");
>> +
>> +static int bpf_mt_check(const struct xt_mtchk_param *par)
>> +{
>> +     struct xt_bpf_info *info = par->matchinfo;
>> +     const struct xt_entry_match *match;
>> +     struct sock_fprog program;
>> +     int expected_len;
>> +
>> +     match = container_of(par->matchinfo, const struct xt_entry_match, data);
>> +     expected_len = sizeof(struct xt_entry_match) +
>> +                    sizeof(struct xt_bpf_info) +
>> +                    (sizeof(struct sock_filter) *
>> +                     info->bpf_program_num_elem);
>> +
>> +     if (match->u.match_size != expected_len) {
>> +             pr_info("bpf: check failed: incorrect length\n");
>> +             return -EINVAL;
>> +     }
>> +
>> +     program.len = info->bpf_program_num_elem;
>> +     program.filter = info->bpf_program;
>> +     if (sk_unattached_filter_create(&info->filter, &program)) {
>> +             pr_info("bpf: check failed: parse error\n");
>> +             return -EINVAL;
>> +     }
>> +
>> +     return 0;
>> +}
>> +
>> +static bool bpf_mt(const struct sk_buff *skb, struct xt_action_param *par)
>> +{
>> +     const struct xt_bpf_info *info = par->matchinfo;
>> +
>> +     return SK_RUN_FILTER(info->filter, skb);
>> +}
>> +
>> +static void bpf_mt_destroy(const struct xt_mtdtor_param *par)
>> +{
>> +     const struct xt_bpf_info *info = par->matchinfo;
>> +     sk_unattached_filter_destroy(info->filter);
>> +}
>> +
>> +static struct xt_match bpf_mt_reg __read_mostly = {
>> +     .name           = "bpf",
>> +     .revision       = 0,
>> +     .family         = NFPROTO_UNSPEC,
>> +     .checkentry     = bpf_mt_check,
>> +     .match          = bpf_mt,
>> +     .destroy        = bpf_mt_destroy,
>> +     .matchsize      = -1, /* skip xt_check_match because of dynamic len */
>> +     .me             = THIS_MODULE,
>> +};
>> +
>> +static int __init bpf_mt_init(void)
>> +{
>> +     return xt_register_match(&bpf_mt_reg);
>> +}
>> +
>> +static void __exit bpf_mt_exit(void)
>> +{
>> +     xt_unregister_match(&bpf_mt_reg);
>> +}
>> +
>> +module_init(bpf_mt_init);
>> +module_exit(bpf_mt_exit);
>> --
>> 1.7.7.3
>>
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Pablo Neira - Dec. 7, 2012, 1:16 p.m.
On Wed, Dec 05, 2012 at 03:10:13PM -0500, Willem de Bruijn wrote:
> On Wed, Dec 5, 2012 at 2:48 PM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > Hi Willem,
> >
> > On Wed, Dec 05, 2012 at 02:22:19PM -0500, Willem de Bruijn wrote:
> >> A new match that executes sk_run_filter on every packet. BPF filters
> >> can access skbuff fields that are out of scope for existing iptables
> >> rules, allow more expressive logic, and on platforms with JIT support
> >> can even be faster.
> >>
> >> I have a corresponding iptables patch that takes `tcpdump -ddd`
> >> output, as used in the examples below. The two parts communicate
> >> using a variable length structure. This is similar to ebt_among,
> >> but new for iptables.
> >>
> >> Verified functionality by inserting an ip source filter on chain
> >> INPUT and an ip dest filter on chain OUTPUT and noting that ping
> >> failed while a rule was active:
> >>
> >> iptables -v -A INPUT -m bpf --bytecode '4,32 0 0 12,21 0 1 $SADDR,6 0 0 96,6 0 0 0,' -j DROP
> >> iptables -v -A OUTPUT -m bpf --bytecode '4,32 0 0 16,21 0 1 $DADDR,6 0 0 96,6 0 0 0,' -j DROP
> >
> > I like this BPF idea for iptables.
> >
> > I made a similar extension time ago, but it was taking a file as
> > parameter. That file contained in BPF code. I made a simple bison
> > parser that takes BPF code and put it into the bpf array of
> > instructions. It would be a bit more intuitive to define a filter and
> > we can distribute it with iptables.
> 
> That's cleaner, indeed. I actually like how tcpdump operates as a
> code generator if you pass -ddd. Unfortunately, it generates code only
> for link layer types of its supported devices, such as DLT_EN10MB and
> DLT_LINUX_SLL. The network layer interface of basic iptables
> (forgetting device dependent mechanisms as used in xt_mac) is DLT_RAW,
> but that is rarely supported.

Indeed, you'll have to hack on tcpdump to select the offset. In
iptables the base is the layer 3 header. With that change you could
use tcpdump for generate code automagically from their syntax.

> > Let me check on my internal trees, I can put that user-space code
> > somewhere in case you're interested.
> 
> Absolutely. I'll be happy to revise to get it in. I'm also considering
> sending a patch to tcpdump to make it generate code independent of the
> installed hardware when specifying -y.

I found a version of the old parser code I made:

http://1984.lsi.us.es/git/nfbpf/

It interprets a filter expressed in a similar way to tcpdump -dd but
it's using the BPF constants. It's quite preliminary and simple if you
look at the code.

Extending it to interpret some syntax similar to tcpdump -d would even
make more readable the BPF filter.

Time ago I also thought about taking the kernel code that checks that
the filter is correct. Currently you get -EINVAL if you pass a
handcrafted filter which is incorrect, so it's hard task to debug what
you made wrong.

It could be added to the iptables tree. Or if generic enough for BPF
and the effort is worth, just provide some small library that iptables
can link with and a small compiler/checker to help people develop BPF
filters.

Back to your xt_bpf thing, we can use the file containing the code
instead:

iptables -v -A INPUT -m bpf --bytecode-file filter1.bpf -j DROP
iptables -v -A OUTPUT -m bpf --bytecode-file filter2.bpf -j DROP

We can still allow the inlined filter via --bytecode if you want.
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Willem de Bruijn - Dec. 7, 2012, 4:56 p.m.
On Fri, Dec 7, 2012 at 8:16 AM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> On Wed, Dec 05, 2012 at 03:10:13PM -0500, Willem de Bruijn wrote:
>> On Wed, Dec 5, 2012 at 2:48 PM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
>> > Hi Willem,
>> >
>> > On Wed, Dec 05, 2012 at 02:22:19PM -0500, Willem de Bruijn wrote:
>> >> A new match that executes sk_run_filter on every packet. BPF filters
>> >> can access skbuff fields that are out of scope for existing iptables
>> >> rules, allow more expressive logic, and on platforms with JIT support
>> >> can even be faster.
>> >>
>> >> I have a corresponding iptables patch that takes `tcpdump -ddd`
>> >> output, as used in the examples below. The two parts communicate
>> >> using a variable length structure. This is similar to ebt_among,
>> >> but new for iptables.
>> >>
>> >> Verified functionality by inserting an ip source filter on chain
>> >> INPUT and an ip dest filter on chain OUTPUT and noting that ping
>> >> failed while a rule was active:
>> >>
>> >> iptables -v -A INPUT -m bpf --bytecode '4,32 0 0 12,21 0 1 $SADDR,6 0 0 96,6 0 0 0,' -j DROP
>> >> iptables -v -A OUTPUT -m bpf --bytecode '4,32 0 0 16,21 0 1 $DADDR,6 0 0 96,6 0 0 0,' -j DROP
>> >
>> > I like this BPF idea for iptables.
>> >
>> > I made a similar extension time ago, but it was taking a file as
>> > parameter. That file contained in BPF code. I made a simple bison
>> > parser that takes BPF code and put it into the bpf array of
>> > instructions. It would be a bit more intuitive to define a filter and
>> > we can distribute it with iptables.
>>
>> That's cleaner, indeed. I actually like how tcpdump operates as a
>> code generator if you pass -ddd. Unfortunately, it generates code only
>> for link layer types of its supported devices, such as DLT_EN10MB and
>> DLT_LINUX_SLL. The network layer interface of basic iptables
>> (forgetting device dependent mechanisms as used in xt_mac) is DLT_RAW,
>> but that is rarely supported.
>
> Indeed, you'll have to hack on tcpdump to select the offset. In
> iptables the base is the layer 3 header. With that change you could
> use tcpdump for generate code automagically from their syntax.
>
>> > Let me check on my internal trees, I can put that user-space code
>> > somewhere in case you're interested.
>>
>> Absolutely. I'll be happy to revise to get it in. I'm also considering
>> sending a patch to tcpdump to make it generate code independent of the
>> installed hardware when specifying -y.
>
> I found a version of the old parser code I made:
>
> http://1984.lsi.us.es/git/nfbpf/
>
> It interprets a filter expressed in a similar way to tcpdump -dd but
> it's using the BPF constants. It's quite preliminary and simple if you
> look at the code.
>
> Extending it to interpret some syntax similar to tcpdump -d would even
> make more readable the BPF filter.
>
> Time ago I also thought about taking the kernel code that checks that
> the filter is correct. Currently you get -EINVAL if you pass a
> handcrafted filter which is incorrect, so it's hard task to debug what
> you made wrong.
>
> It could be added to the iptables tree. Or if generic enough for BPF
> and the effort is worth, just provide some small library that iptables
> can link with and a small compiler/checker to help people develop BPF
> filters.

Or use pcap_compile? I went with the tcpdump output to avoid
introducing a direct dependency on pcap to iptables. One possible
downside I see to pcap_compile vs. developing from scratch is that it
might lag in supporting the LSF ancillary data fields.

> Back to your xt_bpf thing, we can use the file containing the code
> instead:
>
> iptables -v -A INPUT -m bpf --bytecode-file filter1.bpf -j DROP
> iptables -v -A OUTPUT -m bpf --bytecode-file filter2.bpf -j DROP
>
> We can still allow the inlined filter via --bytecode if you want.

I'll add that. I'd like to keep --bytecode to able to generate the
code inline using backticks.
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Pablo Neira - Dec. 8, 2012, 3:31 a.m.
On Fri, Dec 07, 2012 at 11:56:05AM -0500, Willem de Bruijn wrote:
> On Fri, Dec 7, 2012 at 8:16 AM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > On Wed, Dec 05, 2012 at 03:10:13PM -0500, Willem de Bruijn wrote:
> >> On Wed, Dec 5, 2012 at 2:48 PM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> >> > Hi Willem,
> >> >
> >> > On Wed, Dec 05, 2012 at 02:22:19PM -0500, Willem de Bruijn wrote:
> >> >> A new match that executes sk_run_filter on every packet. BPF filters
> >> >> can access skbuff fields that are out of scope for existing iptables
> >> >> rules, allow more expressive logic, and on platforms with JIT support
> >> >> can even be faster.
> >> >>
> >> >> I have a corresponding iptables patch that takes `tcpdump -ddd`
> >> >> output, as used in the examples below. The two parts communicate
> >> >> using a variable length structure. This is similar to ebt_among,
> >> >> but new for iptables.
> >> >>
> >> >> Verified functionality by inserting an ip source filter on chain
> >> >> INPUT and an ip dest filter on chain OUTPUT and noting that ping
> >> >> failed while a rule was active:
> >> >>
> >> >> iptables -v -A INPUT -m bpf --bytecode '4,32 0 0 12,21 0 1 $SADDR,6 0 0 96,6 0 0 0,' -j DROP
> >> >> iptables -v -A OUTPUT -m bpf --bytecode '4,32 0 0 16,21 0 1 $DADDR,6 0 0 96,6 0 0 0,' -j DROP
> >> >
> >> > I like this BPF idea for iptables.
> >> >
> >> > I made a similar extension time ago, but it was taking a file as
> >> > parameter. That file contained in BPF code. I made a simple bison
> >> > parser that takes BPF code and put it into the bpf array of
> >> > instructions. It would be a bit more intuitive to define a filter and
> >> > we can distribute it with iptables.
> >>
> >> That's cleaner, indeed. I actually like how tcpdump operates as a
> >> code generator if you pass -ddd. Unfortunately, it generates code only
> >> for link layer types of its supported devices, such as DLT_EN10MB and
> >> DLT_LINUX_SLL. The network layer interface of basic iptables
> >> (forgetting device dependent mechanisms as used in xt_mac) is DLT_RAW,
> >> but that is rarely supported.
> >
> > Indeed, you'll have to hack on tcpdump to select the offset. In
> > iptables the base is the layer 3 header. With that change you could
> > use tcpdump for generate code automagically from their syntax.
> >
> >> > Let me check on my internal trees, I can put that user-space code
> >> > somewhere in case you're interested.
> >>
> >> Absolutely. I'll be happy to revise to get it in. I'm also considering
> >> sending a patch to tcpdump to make it generate code independent of the
> >> installed hardware when specifying -y.
> >
> > I found a version of the old parser code I made:
> >
> > http://1984.lsi.us.es/git/nfbpf/
> >
> > It interprets a filter expressed in a similar way to tcpdump -dd but
> > it's using the BPF constants. It's quite preliminary and simple if you
> > look at the code.
> >
> > Extending it to interpret some syntax similar to tcpdump -d would even
> > make more readable the BPF filter.
> >
> > Time ago I also thought about taking the kernel code that checks that
> > the filter is correct. Currently you get -EINVAL if you pass a
> > handcrafted filter which is incorrect, so it's hard task to debug what
> > you made wrong.
> >
> > It could be added to the iptables tree. Or if generic enough for BPF
> > and the effort is worth, just provide some small library that iptables
> > can link with and a small compiler/checker to help people develop BPF
> > filters.
> 
> Or use pcap_compile? I went with the tcpdump output to avoid
> introducing a direct dependency on pcap to iptables. One possible
> downside I see to pcap_compile vs. developing from scratch is that it
> might lag in supporting the LSF ancillary data fields.

I suggest to put the code of that preliminary nfbpf utility into
iptables to allow to read the BPF filters from a file and put them
into the BPF array of instructions. I can help with that.

> > Back to your xt_bpf thing, we can use the file containing the code
> > instead:
> >
> > iptables -v -A INPUT -m bpf --bytecode-file filter1.bpf -j DROP
> > iptables -v -A OUTPUT -m bpf --bytecode-file filter2.bpf -j DROP
> >
> > We can still allow the inlined filter via --bytecode if you want.
> 
> I'll add that. I'd like to keep --bytecode to able to generate the
> code inline using backticks.

As said, I'm fine with that, but I'll be really happy if we can
provide some utility to generate that code using backticks for the
masses (in case they want to pass it inlined in that format).
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danborkmann@iogearbox.net - Dec. 8, 2012, 4:02 p.m.
On Sat, Dec 8, 2012 at 4:31 AM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> On Fri, Dec 07, 2012 at 11:56:05AM -0500, Willem de Bruijn wrote:
>> On Fri, Dec 7, 2012 at 8:16 AM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
>> > On Wed, Dec 05, 2012 at 03:10:13PM -0500, Willem de Bruijn wrote:
>> >> On Wed, Dec 5, 2012 at 2:48 PM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
>> >> > Hi Willem,
>> >> >
>> >> > On Wed, Dec 05, 2012 at 02:22:19PM -0500, Willem de Bruijn wrote:
>> >> >> A new match that executes sk_run_filter on every packet. BPF filters
>> >> >> can access skbuff fields that are out of scope for existing iptables
>> >> >> rules, allow more expressive logic, and on platforms with JIT support
>> >> >> can even be faster.
>> >> >>
>> >> >> I have a corresponding iptables patch that takes `tcpdump -ddd`
>> >> >> output, as used in the examples below. The two parts communicate
>> >> >> using a variable length structure. This is similar to ebt_among,
>> >> >> but new for iptables.
>> >> >>
>> >> >> Verified functionality by inserting an ip source filter on chain
>> >> >> INPUT and an ip dest filter on chain OUTPUT and noting that ping
>> >> >> failed while a rule was active:
>> >> >>
>> >> >> iptables -v -A INPUT -m bpf --bytecode '4,32 0 0 12,21 0 1 $SADDR,6 0 0 96,6 0 0 0,' -j DROP
>> >> >> iptables -v -A OUTPUT -m bpf --bytecode '4,32 0 0 16,21 0 1 $DADDR,6 0 0 96,6 0 0 0,' -j DROP
>> >> >
>> >> > I like this BPF idea for iptables.
>> >> >
>> >> > I made a similar extension time ago, but it was taking a file as
>> >> > parameter. That file contained in BPF code. I made a simple bison
>> >> > parser that takes BPF code and put it into the bpf array of
>> >> > instructions. It would be a bit more intuitive to define a filter and
>> >> > we can distribute it with iptables.
>> >>
>> >> That's cleaner, indeed. I actually like how tcpdump operates as a
>> >> code generator if you pass -ddd. Unfortunately, it generates code only
>> >> for link layer types of its supported devices, such as DLT_EN10MB and
>> >> DLT_LINUX_SLL. The network layer interface of basic iptables
>> >> (forgetting device dependent mechanisms as used in xt_mac) is DLT_RAW,
>> >> but that is rarely supported.
>> >
>> > Indeed, you'll have to hack on tcpdump to select the offset. In
>> > iptables the base is the layer 3 header. With that change you could
>> > use tcpdump for generate code automagically from their syntax.
>> >
>> >> > Let me check on my internal trees, I can put that user-space code
>> >> > somewhere in case you're interested.
>> >>
>> >> Absolutely. I'll be happy to revise to get it in. I'm also considering
>> >> sending a patch to tcpdump to make it generate code independent of the
>> >> installed hardware when specifying -y.
>> >
>> > I found a version of the old parser code I made:
>> >
>> > http://1984.lsi.us.es/git/nfbpf/
>> >
>> > It interprets a filter expressed in a similar way to tcpdump -dd but
>> > it's using the BPF constants. It's quite preliminary and simple if you
>> > look at the code.
>> >
>> > Extending it to interpret some syntax similar to tcpdump -d would even
>> > make more readable the BPF filter.
>> >
>> > Time ago I also thought about taking the kernel code that checks that
>> > the filter is correct. Currently you get -EINVAL if you pass a
>> > handcrafted filter which is incorrect, so it's hard task to debug what
>> > you made wrong.
>> >
>> > It could be added to the iptables tree. Or if generic enough for BPF
>> > and the effort is worth, just provide some small library that iptables
>> > can link with and a small compiler/checker to help people develop BPF
>> > filters.
>>
>> Or use pcap_compile? I went with the tcpdump output to avoid
>> introducing a direct dependency on pcap to iptables. One possible
>> downside I see to pcap_compile vs. developing from scratch is that it
>> might lag in supporting the LSF ancillary data fields.
>
> I suggest to put the code of that preliminary nfbpf utility into
> iptables to allow to read the BPF filters from a file and put them
> into the BPF array of instructions. I can help with that.
>
>> > Back to your xt_bpf thing, we can use the file containing the code
>> > instead:
>> >
>> > iptables -v -A INPUT -m bpf --bytecode-file filter1.bpf -j DROP
>> > iptables -v -A OUTPUT -m bpf --bytecode-file filter2.bpf -j DROP
>> >
>> > We can still allow the inlined filter via --bytecode if you want.
>>
>> I'll add that. I'd like to keep --bytecode to able to generate the
>> code inline using backticks.
>
> As said, I'm fine with that, but I'll be really happy if we can
> provide some utility to generate that code using backticks for the
> masses (in case they want to pass it inlined in that format).

If it helps, you could use "bpfc", or rip-off its code to not have a
dependency; it's part of the netsniff-ng toolkit.

It can be used like:

bpfc examples/bpfc/arp.bpf
{ 0x28, 0, 0, 0x0000000c },
{ 0x15, 0, 1, 0x00000806 },
{ 0x6, 0, 0, 0xffffffff },
{ 0x6, 0, 0, 0x00000000 },

where arp.bpf is, for instance:

_main:
  ldh [12]
  jeq #0x806, keep, drop
keep:
  ret #0xffffffff
drop:
  ret #0

"Core" files are: src/bpf_lexer.l, src/bpf_parser.y

It also supports all Linux ANC-operations that were added to the
kernel (like VLAN, XOR and so on). I started but didn't have time to
continue a higher-level language for that, that would translate to
such an example above (which then translates again to opcodes).
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Patch

diff --git a/include/linux/netfilter/xt_bpf.h b/include/linux/netfilter/xt_bpf.h
new file mode 100644
index 0000000..23502c0
--- /dev/null
+++ b/include/linux/netfilter/xt_bpf.h
@@ -0,0 +1,17 @@ 
+#ifndef _XT_BPF_H
+#define _XT_BPF_H
+
+#include <linux/filter.h>
+#include <linux/types.h>
+
+struct xt_bpf_info {
+	__u16 bpf_program_num_elem;
+
+	/* only used in kernel */
+	struct sk_filter *filter __attribute__((aligned(8)));
+
+	/* variable size, based on program_num_elem */
+	struct sock_filter bpf_program[0];
+};
+
+#endif /*_XT_BPF_H */
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index c9739c6..c7cc0b8 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -798,6 +798,15 @@  config NETFILTER_XT_MATCH_ADDRTYPE
 	  If you want to compile it as a module, say M here and read
 	  <file:Documentation/kbuild/modules.txt>.  If unsure, say `N'.
 
+config NETFILTER_XT_MATCH_BPF
+	tristate '"bpf" match support'
+	depends on NETFILTER_ADVANCED
+	help
+	  BPF matching applies a linux socket filter to each packet and
+          accepts those for which the filter returns non-zero.
+
+	  To compile it as a module, choose M here.  If unsure, say N.
+
 config NETFILTER_XT_MATCH_CLUSTER
 	tristate '"cluster" match support'
 	depends on NF_CONNTRACK
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 8e5602f..9f12eeb 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -98,6 +98,7 @@  obj-$(CONFIG_NETFILTER_XT_TARGET_IDLETIMER) += xt_IDLETIMER.o
 
 # matches
 obj-$(CONFIG_NETFILTER_XT_MATCH_ADDRTYPE) += xt_addrtype.o
+obj-$(CONFIG_NETFILTER_XT_MATCH_BPF) += xt_bpf.o
 obj-$(CONFIG_NETFILTER_XT_MATCH_CLUSTER) += xt_cluster.o
 obj-$(CONFIG_NETFILTER_XT_MATCH_COMMENT) += xt_comment.o
 obj-$(CONFIG_NETFILTER_XT_MATCH_CONNBYTES) += xt_connbytes.o
diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 8d987c3..26306be 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -379,8 +379,9 @@  int xt_check_match(struct xt_mtchk_param *par,
 	if (XT_ALIGN(par->match->matchsize) != size &&
 	    par->match->matchsize != -1) {
 		/*
-		 * ebt_among is exempt from centralized matchsize checking
-		 * because it uses a dynamic-size data set.
+		 * matches of variable size length, such as ebt_among,
+		 * are exempt from centralized matchsize checking. They
+		 * skip the test by setting xt_match.matchsize to -1.
 		 */
 		pr_err("%s_tables: %s.%u match: invalid size "
 		       "%u (kernel) != (user) %u\n",
diff --git a/net/netfilter/xt_bpf.c b/net/netfilter/xt_bpf.c
new file mode 100644
index 0000000..07077c5
--- /dev/null
+++ b/net/netfilter/xt_bpf.c
@@ -0,0 +1,88 @@ 
+/* Xtables module to match packets using a BPF filter.
+ * Copyright 2012 Google Inc.
+ * Written by Willem de Bruijn <willemb@google.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/ipv6.h>
+#include <linux/filter.h>
+#include <net/ip.h>
+
+#include <linux/netfilter/xt_bpf.h>
+#include <linux/netfilter/x_tables.h>
+
+MODULE_AUTHOR("Willem de Bruijn <willemb@google.com>");
+MODULE_DESCRIPTION("Xtables: BPF filter match");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("ipt_bpf");
+MODULE_ALIAS("ip6t_bpf");
+
+static int bpf_mt_check(const struct xt_mtchk_param *par)
+{
+	struct xt_bpf_info *info = par->matchinfo;
+	const struct xt_entry_match *match;
+	struct sock_fprog program;
+	int expected_len;
+
+	match = container_of(par->matchinfo, const struct xt_entry_match, data);
+	expected_len = sizeof(struct xt_entry_match) +
+		       sizeof(struct xt_bpf_info) +
+		       (sizeof(struct sock_filter) *
+			info->bpf_program_num_elem);
+
+	if (match->u.match_size != expected_len) {
+		pr_info("bpf: check failed: incorrect length\n");
+		return -EINVAL;
+	}
+
+	program.len = info->bpf_program_num_elem;
+	program.filter = info->bpf_program;
+	if (sk_unattached_filter_create(&info->filter, &program)) {
+		pr_info("bpf: check failed: parse error\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static bool bpf_mt(const struct sk_buff *skb, struct xt_action_param *par)
+{
+	const struct xt_bpf_info *info = par->matchinfo;
+
+	return SK_RUN_FILTER(info->filter, skb);
+}
+
+static void bpf_mt_destroy(const struct xt_mtdtor_param *par)
+{
+	const struct xt_bpf_info *info = par->matchinfo;
+	sk_unattached_filter_destroy(info->filter);
+}
+
+static struct xt_match bpf_mt_reg __read_mostly = {
+	.name		= "bpf",
+	.revision	= 0,
+	.family		= NFPROTO_UNSPEC,
+	.checkentry	= bpf_mt_check,
+	.match		= bpf_mt,
+	.destroy	= bpf_mt_destroy,
+	.matchsize	= -1, /* skip xt_check_match because of dynamic len */
+	.me		= THIS_MODULE,
+};
+
+static int __init bpf_mt_init(void)
+{
+	return xt_register_match(&bpf_mt_reg);
+}
+
+static void __exit bpf_mt_exit(void)
+{
+	xt_unregister_match(&bpf_mt_reg);
+}
+
+module_init(bpf_mt_init);
+module_exit(bpf_mt_exit);