Subject: Re: [PATCHv2 net-next] netfilter: add IPv4/6 IPComp extension match support

From: Pablo Neira Ayuso <[email-masked]>
Date: Tue, 24 Dec 2013 19:27:16 +0100

On Wed, Dec 18, 2013 at 11:27:02AM +0800, Fan Du wrote:
> With this plugin, user could specify IPComp tagged with certain
> CPI that host not interested will be DROPped or any other action.
> 
> For example:
> iptables  -A INPUT -p 108 -m ipcomp --ipcompspi 0x87 -j DROP
> ip6tables -A INPUT -p 108 -m ipcomp --ipcompspi 0x87 -j DROP
> 
> Then input IPComp packet with CPI equates 0x87 will not reach
> upper layer anymore.

Applied this patch with minor glitches, see below.

> Signed-off-by: Fan Du <[email-masked]>
> ---
> v2:
>   Consolidate net/ipv4/netfilter/ipt_comp.c and net/ipv6/netfilter/ip6t_comp.c
>   into one piece, as per Pablo suggestion.
> ---
>  include/uapi/linux/netfilter/xt_comp.h |   16 +++++
>  net/netfilter/Kconfig                  |    9 +++
>  net/netfilter/Makefile                 |    1 +
>  net/netfilter/xt_ipcomp.c              |  112 ++++++++++++++++++++++++++++++++
>  4 files changed, 138 insertions(+)
>  create mode 100644 include/uapi/linux/netfilter/xt_comp.h
>  create mode 100644 net/netfilter/xt_ipcomp.c
> 
> diff --git a/include/uapi/linux/netfilter/xt_comp.h b/include/uapi/linux/netfilter/xt_comp.h
> new file mode 100644
> index 0000000..5e4abb3
> --- /dev/null
> +++ b/include/uapi/linux/netfilter/xt_comp.h
> @@ -0,0 +1,16 @@
> +#ifndef _IPT_COMP_H
> +#define _IPT_COMP_H

Renamed this to _XT_COMP_H_

> +
> +#include <linux/types.h>
> +
> +struct ipt_comp {

Renamed this structure to xt_ipcomp.

> +	__u32 spis[2];	/* Security Parameter Index */
> +	__u8 invflags;	/* Inverse flags */
> +	__u8 hdrres;	/* Test of the Reserved Filed */
> +};
> +
> +/* Values for "invflags" field in struct ipt_comp. */
> +#define IPT_IPCOMP_INV_SPI	0x01	/* Invert the sense of spi. */
> +#define IPT_IPCOMP_INV_MASK	0x01	/* All possible flags. */

IPT_ to XT_

> +
> +#endif /*_IPT_COMP_H*/
> diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
> index c3398cd..d3242fc 100644
> --- a/net/netfilter/Kconfig
> +++ b/net/netfilter/Kconfig
> @@ -1002,6 +1002,15 @@ config NETFILTER_XT_MATCH_ESP
>  
>  	  To compile it as a module, choose M here.  If unsure, say N.
>  
> +config NETFILTER_XT_MATCH_IPCOMP

Fixed wrong ordering, NETFILTER_XT_MATCH_IPCOMP should come before
IPRANGE (as Kconfig is alphabetically ordered).

> +	tristate '"ipcomp" match support'
> +	depends on NETFILTER_ADVANCED
> +	help
> +	  This match extension allows you to match a range of CPIs(16 bits)
> +	  inside IPComp header of IPSec packets.
> +
> +	  To compile it as a module, choose M here.  If unsure, say N.
> +
>  config NETFILTER_XT_MATCH_HASHLIMIT
>  	tristate '"hashlimit" match support'
>  	depends on (IP6_NF_IPTABLES || IP6_NF_IPTABLES=n)
> diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
> index 394483b..5369043 100644
> --- a/net/netfilter/Makefile
> +++ b/net/netfilter/Makefile
> @@ -130,6 +130,7 @@ obj-$(CONFIG_NETFILTER_XT_MATCH_DEVGROUP) += xt_devgroup.o
>  obj-$(CONFIG_NETFILTER_XT_MATCH_DSCP) += xt_dscp.o
>  obj-$(CONFIG_NETFILTER_XT_MATCH_ECN) += xt_ecn.o
>  obj-$(CONFIG_NETFILTER_XT_MATCH_ESP) += xt_esp.o
> +obj-$(CONFIG_NETFILTER_XT_MATCH_IPCOMP) += xt_ipcomp.o

fixed ordering here as well.

>  obj-$(CONFIG_NETFILTER_XT_MATCH_HASHLIMIT) += xt_hashlimit.o
>  obj-$(CONFIG_NETFILTER_XT_MATCH_HELPER) += xt_helper.o
>  obj-$(CONFIG_NETFILTER_XT_MATCH_HL) += xt_hl.o
> diff --git a/net/netfilter/xt_ipcomp.c b/net/netfilter/xt_ipcomp.c
> new file mode 100644
> index 0000000..e856514
> --- /dev/null
> +++ b/net/netfilter/xt_ipcomp.c
> @@ -0,0 +1,112 @@
> +/*  Kernel module to match IPComp parameters for IPv4 and IPv6
> + *
> + *  Copyright (C) 2013 WindRiver
> + *
> + *  Author:
> + *  Fan Du <[email-masked]>
> + *
> + *  Based on:
> + *  net/netfilter/xt_esp.c
> + *
> + *  This program is free software; you can redistribute it and/or
> + *  modify it under the terms of the GNU General Public License
> + *  as published by the Free Software Foundation; either version
> + *  2 of the License, or (at your option) any later version.
> + */
> +
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +#include <linux/in.h>
> +#include <linux/module.h>
> +#include <linux/skbuff.h>
> +#include <linux/ip.h>
> +
> +#include <linux/netfilter/xt_comp.h>
> +#include <linux/netfilter/x_tables.h>
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Fan Du <[email-masked]>");
> +MODULE_DESCRIPTION("Xtables: IPv4 IPsec-IPComp SPI match");
                                   ^
Indicated Ipv6 here as well.

> +
> +/* Returns 1 if the spi is matched by the range, 0 otherwise */
> +static inline bool
> +spi_match(u_int32_t min, u_int32_t max, u_int32_t spi, bool invert)
> +{
> +	bool r;
> +	pr_debug("spi_match:%c 0x%x <= 0x%x <= 0x%x\n",
> +		 invert ? '!' : ' ', min, spi, max);
> +	r = (spi >= min && spi <= max) ^ invert;
> +	pr_debug(" result %s\n", r ? "PASS" : "FAILED");
> +	return r;
> +}
> +
> +static bool comp_mt(const struct sk_buff *skb, struct xt_action_param *par)
> +{
> +	struct ip_comp_hdr _comphdr;
> +	const struct ip_comp_hdr *chdr;
> +	const struct ipt_comp *compinfo = par->matchinfo;
> +
> +	/* Must not be a fragment. */
> +	if (par->fragoff != 0)
> +		return false;
> +
> +	chdr = skb_header_pointer(skb, par->thoff, sizeof(_comphdr), &_comphdr);
> +	if (chdr == NULL) {
> +		/* We've been asked to examine this packet, and we
> +		 * can't.  Hence, no choice but to drop.
> +		 */
> +		pr_debug("Dropping evil IPComp tinygram.\n");
> +		par->hotdrop = true;
> +		return 0;
> +	}
> +
> +	return spi_match(compinfo->spis[0], compinfo->spis[1],
> +			 ntohl(chdr->cpi << 16),
> +			 !!(compinfo->invflags & IPT_IPCOMP_INV_SPI));
> +}
> +
> +static int comp_mt_check(const struct xt_mtchk_param *par)
> +{
> +	const struct ipt_comp *compinfo = par->matchinfo;
> +
> +	/* Must specify no unknown invflags */
> +	if (compinfo->invflags & ~IPT_IPCOMP_INV_MASK) {
> +		pr_debug("unknown flags %X\n", compinfo->invflags);

changed this to pr_err.

> +		return -EINVAL;
> +	}
> +	return 0;
> +}
> +
> +static struct xt_match comp_mt_reg[] __read_mostly = {
> +	{
> +		.name		= "ipcomp",
> +		.family		= NFPROTO_IPV4,
> +		.match		= comp_mt,
> +		.matchsize	= sizeof(struct ipt_comp),
> +		.proto		= IPPROTO_COMP,
> +		.checkentry	= comp_mt_check,
> +		.me		= THIS_MODULE,
> +	},
> +	{
> +		.name		= "ipcomp",
> +		.family		= NFPROTO_IPV6,
> +		.match		= comp_mt,
> +		.matchsize	= sizeof(struct ipt_comp),
> +		.proto		= IPPROTO_COMP,
> +		.checkentry	= comp_mt_check,
> +		.me		= THIS_MODULE,
> +	},
> +};
> +
> +static int __init comp_mt_init(void)
> +{
> +	return xt_register_matches(comp_mt_reg, ARRAY_SIZE(comp_mt_reg));
> +}
> +
> +static void __exit comp_mt_exit(void)
> +{
> +	xt_unregister_matches(comp_mt_reg, ARRAY_SIZE(comp_mt_reg));
> +}
> +
> +module_init(comp_mt_init);
> +module_exit(comp_mt_exit);
> -- 
> 1.7.9.5
>