Subject: Re: [PATCH 2/2] Interface group match

From: Patrick McHardy <[email-masked]>
Date: Thu, 18 Oct 2007 12:27:15 +0200

Laszlo Attila Toth wrote:
> Interface group values can be checked on both input and output interfaces.
> 
> Signed-off-by: Laszlo Attila Toth <[email-masked]>
> ---
>  include/linux/netfilter/xt_ifgroup.h |   18 ++++++
>  net/netfilter/Kconfig                |   16 +++++
>  net/netfilter/Makefile               |    1 +
>  net/netfilter/xt_ifgroup.c           |  108 ++++++++++++++++++++++++++++++++++
>  4 files changed, 143 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/netfilter/xt_ifgroup.h b/include/linux/netfilter/xt_ifgroup.h
> new file mode 100644
> index 0000000..9ac75de
> --- /dev/null
> +++ b/include/linux/netfilter/xt_ifgroup.h
> @@ -0,0 +1,18 @@
> +#ifndef _XT_IFGROUP_H
> +#define _XT_IFGROUP_H
> +
> +#define XT_IFGROUP_INVERT_IN	0x01
> +#define XT_IFGROUP_INVERT_OUT	0x02
> +#define XT_IFGROUP_MATCH_IN	0x04
> +#define XT_IFGROUP_MATCH_OUT	0x08		
> +
> +struct xt_ifgroup_info {
> +	u_int32_t in_group;
> +	u_int32_t in_mask;
> +	u_int32_t out_group;
> +	u_int32_t out_mask;
> +	u_int8_t flags;
> +};
> +
> +#endif /*_XT_IFGROUP_H*/
> +
> diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
> index 3599770..0864e19 100644
> --- a/net/netfilter/Kconfig
> +++ b/net/netfilter/Kconfig
> @@ -597,6 +597,22 @@ config NETFILTER_XT_MATCH_QUOTA
>  	  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_IFGROUP
> +	tristate '"ifgroup" interface group match support'
> +	depends on NETFILTER_XTABLES
> +	help
> +	  Interface group matching allows you to match a packet by
> +	  its incoming interface "group", settable using ip link set
> +	  group
> +
> +	  Typical usage is to assign dynamic interfaces to a group
> +	  when they come up using "ip link set group" and then match
> +	  incoming packets with a rule like this:
> +
> +	    iptables -A INPUT -m ifgroup --if-group openvpn-rw1 -j LOG
> +
> +	  To compile it as a module, choose M here.  If unsure, say N.
> +
>  config NETFILTER_XT_MATCH_REALM
>  	tristate  '"realm" match support'
>  	depends on NETFILTER_XTABLES
> diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
> index 0c054bf..da9ab07 100644
> --- a/net/netfilter/Makefile
> +++ b/net/netfilter/Makefile
> @@ -77,3 +77,4 @@ obj-$(CONFIG_NETFILTER_XT_MATCH_TCPMSS) += xt_tcpmss.o
>  obj-$(CONFIG_NETFILTER_XT_MATCH_PHYSDEV) += xt_physdev.o
>  obj-$(CONFIG_NETFILTER_XT_MATCH_U32) += xt_u32.o
>  obj-$(CONFIG_NETFILTER_XT_MATCH_HASHLIMIT) += xt_hashlimit.o
> +obj-$(CONFIG_NETFILTER_XT_MATCH_IFGROUP) += xt_ifgroup.o
> diff --git a/net/netfilter/xt_ifgroup.c b/net/netfilter/xt_ifgroup.c
> new file mode 100644
> index 0000000..07c3acc
> --- /dev/null
> +++ b/net/netfilter/xt_ifgroup.c
> @@ -0,0 +1,108 @@
> +/*
> + * An x_tables match module to match interface groups
> + *
> + * (C) 2006,2007 Balazs Scheidler <[email-masked]>,
> + *   Laszlo Attila Toth <[email-masked]>
> + *
> + * 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/if_ether.h>
> +#include <linux/if_packet.h>

These two look unnecessary.

> +
> +#include <linux/netfilter/xt_ifgroup.h>
> +#include <linux/netfilter/x_tables.h>
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Laszlo Attila Toth <[email-masked]>");
> +MODULE_DESCRIPTION("Xtables interface group matching module");
> +MODULE_ALIAS("ipt_ifgroup");
> +MODULE_ALIAS("ip6t_ifgroup");
> +
> +static bool ifgroup_match(const struct sk_buff *skb,
> +			  const struct net_device *in,
> +			  const struct net_device *out,
> +			  const struct xt_match *match,
> +			  const void *matchinfo,
> +			  int offset,
> +			  unsigned int protoff,
> +			  bool *hotdrop)
> +{
> +#define FLAG_IS_SET(a,b)  ((a & b) == b)
> +#define MATCH_IN  (((in->ifgroup & info->in_mask) == info->in_group) ^ FLAG_IS_SET(info->flags, XT_IFGROUP_INVERT_IN))
> +#define MATCH_OUT (((out->ifgroup & info->out_mask) == info->out_group) ^ FLAG_IS_SET(info->flags, XT_IFGROUP_INVERT_OUT))

Exceeds 80 characters and looks pretty obfuscating. Please open
code this or use an inline function.

> +
> +	const struct xt_ifgroup_info *info = matchinfo;
> +	bool verdict = false;
> +	
> +	if ((info->flags & XT_IFGROUP_MATCH_IN) && (info->flags & XT_IFGROUP_MATCH_OUT))
> +		verdict = MATCH_IN && MATCH_OUT;
> +	else if (info->flags & XT_IFGROUP_MATCH_IN)
> +		verdict = MATCH_IN;
> +	else if (info->flags & XT_IFGROUP_MATCH_OUT)
> +		verdict = MATCH_OUT;

How about:

if (info->flags & XT_IFGROUP_MATCH_IN && !MATCH_IN)
	return false;
if (info->flags & XT_IFGROUP_MATCH_OUT && !MATCH_OUT)
	return false;

instead of having each match twice?

> +	return verdict;
> +}
> +
> +static bool ifgroup_checkentry(const char *tablename, const void *ip_void,
> +			       const struct xt_match *match,
> +			       void *matchinfo, unsigned int hook_mask)
> +{
> +	struct xt_ifgroup_info *info = matchinfo;
> +
> +	if (!(info->flags & (XT_IFGROUP_MATCH_IN|XT_IFGROUP_MATCH_OUT))) {
> +		printk(KERN_ERR "xt_ifgroup: neither incoming nor "
> +				"outgoing device selected\n");
> +		return false;
> +	}
> +	if (hook_mask & (1 << NF_IP_PRE_ROUTING | 1 << NF_IP_LOCAL_IN)
> +	    && info->flags & XT_IFGROUP_MATCH_OUT) {
> +		printk(KERN_ERR "xt_ifgroup: output device not valid in "
> +				"PRE_ROUTING and INPUT\n");
> +		return false;
> +	}
> +	if (hook_mask & (1 << NF_IP_POST_ROUTING | 1 << NF_IP_LOCAL_OUT)
> +	    && info->flags & XT_IFGROUP_MATCH_IN) {
> +		printk(KERN_ERR "xt_ifgroup: input device not valid in "
> +				"POST_ROUTING and OUTPUT\n");
> +		return false;
> +	}
> +	return true;
> +}
> +
> +static struct xt_match xt_ifgroup_match[] __read_mostly  = {
> +        {
> +		.name		= "ifgroup",
> +		.match		= ifgroup_match,
> +		.checkentry	= ifgroup_checkentry,
> +		.matchsize	= sizeof(struct xt_ifgroup_info),
> +		.family		= AF_INET,
> +		.me		= THIS_MODULE,
> +	
> +	},
> +	{
> +		.name		= "ifgroup",
> +		.match		= ifgroup_match,
> +		.checkentry	= ifgroup_checkentry,
> +		.matchsize	= sizeof(struct xt_ifgroup_info),
> +		.family		= AF_INET6,
> +		.me		= THIS_MODULE,
> +	},
> +};
> +
> +static int __init xt_ifgroup_init(void)
> +{
> +	return xt_register_matches(xt_ifgroup_match, ARRAY_SIZE(xt_ifgroup_match));

Also exceeds 80 characters.

> +}
> +
> +static void __exit xt_ifgroup_fini(void)
> +{
> +	xt_unregister_matches(xt_ifgroup_match, ARRAY_SIZE(xt_ifgroup_match));
> +}
> +
> +module_init(xt_ifgroup_init);
> +module_exit(xt_ifgroup_fini);