Re: [PATCH next v3] iptables: add xt_bpf match

[Pablo Neira Ayuso <pablo@netfilter.org>]

Hi Willem,

On Wed, Jan 09, 2013 at 07:15:44PM -0500, Willem de Bruijn wrote:
> Changes:
> - v3: reverted no longer needed changes to x_tables.c
> - v2: use a fixed size match structure to communicate between
>       kernel and userspace.
> 
> Support arbitrary linux socket filter (BPF) programs as iptables
> match rules. This allows for very expressive filters, and on
> platforms with BPF JIT appears competitive with traditional hardcoded
> iptables rules.
> 
> At least, on an x86_64 that achieves 40K netperf TCP_STREAM without
> any iptables rules (40 GBps),
> 
> inserting 100x this bpf rule gives 28K
> 
>     ./iptables -A OUTPUT -m bpf --bytecode '6,40 0 0 14, 21 0 3 2048,48 0 0 25,21 0 1 20,6 0 0 96,6 0 0 0,' -j
> 
>     (as generated by tcpdump -i any -ddd ip proto 20 | tr '\n' ',')

That code generated by tcpdump will not work.

tcpdump generates BPF code assuming that offset 0 is the link layer
header, while iptables considers that offset 0 is the network layer.

More comments below:

> inserting 100x this u32 rule gives 21K
> 
>     ./iptables -A OUTPUT -m u32 --u32 '6&0xFF=0x20' -j DROP
> 
> The two are logically equivalent, as far as I can tell. Let me know
> if my test methodology is flawed in some way. Even in cases where
> slower, the filter adds functionality currently lacking in iptables,
> such as access to sk_buff fields like rxhash and queue_mapping.
> ---
>  include/uapi/linux/netfilter/xt_bpf.h |   17 ++++++++
>  net/netfilter/Kconfig                 |    9 ++++
>  net/netfilter/Makefile                |    1 +
>  net/netfilter/xt_bpf.c                |   73 +++++++++++++++++++++++++++++++++
>  4 files changed, 100 insertions(+), 0 deletions(-)
>  create mode 100644 include/uapi/linux/netfilter/xt_bpf.h
>  create mode 100644 net/netfilter/xt_bpf.c
> 
> diff --git a/include/uapi/linux/netfilter/xt_bpf.h b/include/uapi/linux/netfilter/xt_bpf.h
> new file mode 100644
> index 0000000..5dda450
> --- /dev/null
> +++ b/include/uapi/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>
> +
> +#define XT_BPF_MAX_NUM_INSTR	64
> +
> +struct xt_bpf_info {
> +	__u16 bpf_program_num_elem;
> +	struct sock_filter bpf_program[XT_BPF_MAX_NUM_INSTR];
> +
> +	/* only used in the kernel */
> +	struct sk_filter *filter __attribute__((aligned(8)));
> +};
> +
> +#endif /*_XT_BPF_H */
> diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
> index fefa514..d45720f 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 3259697..6d6194525 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/xt_bpf.c b/net/netfilter/xt_bpf.c
> new file mode 100644
> index 0000000..1bdfab8
> --- /dev/null
> +++ b/net/netfilter/xt_bpf.c
> @@ -0,0 +1,73 @@
> +/* Xtables module to match packets using a BPF filter.
> + * Copyright 2013 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");

Please, add

MODULE_ALIAS("ipt_bpf");
MODULE_ALIAS("ip6t_bpf");

otherwise module auto-loading will not work.

> +
> +static int bpf_mt_check(const struct xt_mtchk_param *par)
> +{
> +	struct xt_bpf_info *info = par->matchinfo;
> +	struct sock_fprog program;
> +
> +	program.len = info->bpf_program_num_elem;
> +	program.filter = info->bpf_program;

sparse reports a warning here above. I've been trying to find a quick
solution, please, have a look at it.

> +	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	= sizeof(struct xt_bpf_info),
> +	.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
>