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Date: Wed, 5 Dec 2012 15:10:13 -0500
From: Willem de Bruijn <willemb@...gle.com>
To: Pablo Neira Ayuso <pablo@...filter.org>
Cc: netfilter-devel <netfilter-devel@...r.kernel.org>,
netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
David Miller <davem@...emloft.net>, kaber <kaber@...sh.net>
Subject: Re: [PATCH 2/2] netfilter: add xt_bpf xtables match
On Wed, Dec 5, 2012 at 2:48 PM, Pablo Neira Ayuso <pablo@...filter.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@...gle.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@...gle.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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