Subject: Re: [PATCH 13/19] netfilter: ip6tables: add MASQUERADE target

From: Pablo Neira Ayuso <[email-masked]>
Date: Fri, 17 Aug 2012 15:11:57 +0200

Hi Patrick,

On Thu, Aug 09, 2012 at 10:08:57PM +0200, [email-masked] wrote:
> From: Patrick McHardy <[email-masked]>
> 
> Signed-off-by: Patrick McHardy <[email-masked]>
> ---
>  include/net/addrconf.h               |    2 +-
>  net/ipv4/netfilter/ipt_MASQUERADE.c  |    3 +-
>  net/ipv6/addrconf.c                  |    2 +-
>  net/ipv6/netfilter/Kconfig           |   12 +++
>  net/ipv6/netfilter/Makefile          |    1 +
>  net/ipv6/netfilter/ip6t_MASQUERADE.c |  135 ++++++++++++++++++++++++++++++++++
>  6 files changed, 152 insertions(+), 3 deletions(-)
>  create mode 100644 net/ipv6/netfilter/ip6t_MASQUERADE.c

Please, add this chunk to this patch:

diff --git a/include/net/netfilter/nf_nat.h
b/include/net/netfilter/nf_nat.h
index 1752f133..bd8eea7 100644
--- a/include/net/netfilter/nf_nat.h
+++ b/include/net/netfilter/nf_nat.h
@@ -43,7 +43,9 @@ struct nf_conn_nat {
        struct nf_conn *ct;
        union nf_conntrack_nat_help help;
 #if defined(CONFIG_IP_NF_TARGET_MASQUERADE) || \
-    defined(CONFIG_IP_NF_TARGET_MASQUERADE_MODULE)
+    defined(CONFIG_IP_NF_TARGET_MASQUERADE_MODULE) || \
+    defined(CONFIG_IP6_NF_TARGET_MASQUERADE) || \
+    defined(CONFIG_IP6_NF_TARGET_MASQUERADE_MODULE)
        int masq_index;
 #endif
 };

Otherwise, compilation breaks with:

* IPv4 NAT is disabled
* IPv6 NAT enabled.

And yes, that pile of ifdefs is really ugly, I wonder if they are
worth for saving 4 bytes. I think most vendors usually include
MASQUERADE support if NAT is enabled.

It seems we have the tradition of keeping several similar compile time
options in Netfilter to optimize memory in several situations (at the
cost of polluting the code with ifdefs). Probably we can think of
getting rid of them.

> diff --git a/include/net/addrconf.h b/include/net/addrconf.h
> index 089a09d..9e63e76 100644
> --- a/include/net/addrconf.h
> +++ b/include/net/addrconf.h
> @@ -78,7 +78,7 @@ extern struct inet6_ifaddr      *ipv6_get_ifaddr(struct net *net,
>  						 int strict);
>  
>  extern int			ipv6_dev_get_saddr(struct net *net,
> -					       struct net_device *dev,
> +					       const struct net_device *dev,
>  					       const struct in6_addr *daddr,
>  					       unsigned int srcprefs,
>  					       struct in6_addr *saddr);
> diff --git a/net/ipv4/netfilter/ipt_MASQUERADE.c b/net/ipv4/netfilter/ipt_MASQUERADE.c
> index 1c3aa28..5d5d4d1 100644
> --- a/net/ipv4/netfilter/ipt_MASQUERADE.c
> +++ b/net/ipv4/netfilter/ipt_MASQUERADE.c
> @@ -99,7 +99,8 @@ device_cmp(struct nf_conn *i, void *ifindex)
>  
>  	if (!nat)
>  		return 0;
> -
> +	if (nf_ct_l3num(i) != NFPROTO_IPV4)
> +		return 0;
>  	return nat->masq_index == (int)(long)ifindex;
>  }
>  
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 7918181..6536404 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -1095,7 +1095,7 @@ out:
>  	return ret;
>  }
>  
> -int ipv6_dev_get_saddr(struct net *net, struct net_device *dst_dev,
> +int ipv6_dev_get_saddr(struct net *net, const struct net_device *dst_dev,
>  		       const struct in6_addr *daddr, unsigned int prefs,
>  		       struct in6_addr *saddr)
>  {
> diff --git a/net/ipv6/netfilter/Kconfig b/net/ipv6/netfilter/Kconfig
> index b27e0ad..54a5032 100644
> --- a/net/ipv6/netfilter/Kconfig
> +++ b/net/ipv6/netfilter/Kconfig
> @@ -144,6 +144,18 @@ config IP6_NF_TARGET_HL
>  	(e.g. when running oldconfig). It selects
>  	CONFIG_NETFILTER_XT_TARGET_HL.
>  
> +config IP6_NF_TARGET_MASQUERADE
> +	tristate "MASQUERADE target support"
> +	depends on NF_NAT_IPV6
> +	help
> +	  Masquerading is a special case of NAT: all outgoing connections are
> +	  changed to seem to come from a particular interface's address, and
> +	  if the interface goes down, those connections are lost.  This is
> +	  only useful for dialup accounts with dynamic IP address (ie. your IP
> +	  address will be different on next dialup).
> +
> +	  To compile it as a module, choose M here.  If unsure, say N.
> +
>  config IP6_NF_FILTER
>  	tristate "Packet filtering"
>  	default m if NETFILTER_ADVANCED=n
> diff --git a/net/ipv6/netfilter/Makefile b/net/ipv6/netfilter/Makefile
> index 7677937..068bad1 100644
> --- a/net/ipv6/netfilter/Makefile
> +++ b/net/ipv6/netfilter/Makefile
> @@ -34,4 +34,5 @@ obj-$(CONFIG_IP6_NF_MATCH_RPFILTER) += ip6t_rpfilter.o
>  obj-$(CONFIG_IP6_NF_MATCH_RT) += ip6t_rt.o
>  
>  # targets
> +obj-$(CONFIG_IP6_NF_TARGET_MASQUERADE) += ip6t_MASQUERADE.o
>  obj-$(CONFIG_IP6_NF_TARGET_REJECT) += ip6t_REJECT.o
> diff --git a/net/ipv6/netfilter/ip6t_MASQUERADE.c b/net/ipv6/netfilter/ip6t_MASQUERADE.c
> new file mode 100644
> index 0000000..60e9053
> --- /dev/null
> +++ b/net/ipv6/netfilter/ip6t_MASQUERADE.c
> @@ -0,0 +1,135 @@
> +/*
> + * Copyright (c) 2011 Patrick McHardy <[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.
> + *
> + * Based on Rusty Russell's IPv6 MASQUERADE target. Development of IPv6
> + * NAT funded by Astaro.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/netdevice.h>
> +#include <linux/ipv6.h>
> +#include <linux/netfilter.h>
> +#include <linux/netfilter_ipv6.h>
> +#include <linux/netfilter/x_tables.h>
> +#include <net/netfilter/nf_nat.h>
> +#include <net/addrconf.h>
> +#include <net/ipv6.h>
> +
> +static unsigned int
> +masquerade_tg6(struct sk_buff *skb, const struct xt_action_param *par)
> +{
> +	const struct nf_nat_range *range = par->targinfo;
> +	enum ip_conntrack_info ctinfo;
> +	struct in6_addr src;
> +	struct nf_conn *ct;
> +	struct nf_nat_range newrange;
> +
> +	ct = nf_ct_get(skb, &ctinfo);
> +	NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED ||
> +			    ctinfo == IP_CT_RELATED_REPLY));
> +
> +	if (ipv6_dev_get_saddr(dev_net(par->out), par->out,
> +			       &ipv6_hdr(skb)->daddr, 0, &src) < 0)
> +		return NF_DROP;
> +
> +	nfct_nat(ct)->masq_index = par->out->ifindex;
> +
> +	newrange.flags		= range->flags | NF_NAT_RANGE_MAP_IPS;
> +	newrange.min_addr.in6	= src;
> +	newrange.max_addr.in6	= src;
> +	newrange.min_proto	= range->min_proto;
> +	newrange.max_proto	= range->max_proto;
> +
> +	return nf_nat_setup_info(ct, &newrange, NF_NAT_MANIP_SRC);
> +}
> +
> +static int masquerade_tg6_checkentry(const struct xt_tgchk_param *par)
> +{
> +	const struct nf_nat_range *range = par->targinfo;
> +
> +	if (range->flags & NF_NAT_RANGE_MAP_IPS)
> +		return -EINVAL;
> +	return 0;
> +}
> +
> +static int device_cmp(struct nf_conn *ct, void *ifindex)
> +{
> +	const struct nf_conn_nat *nat = nfct_nat(ct);
> +
> +	if (!nat)
> +		return 0;
> +	if (nf_ct_l3num(ct) != NFPROTO_IPV6)
> +		return 0;
> +	return nat->masq_index == (int)(long)ifindex;
> +}
> +
> +static int masq_device_event(struct notifier_block *this,
> +			     unsigned long event, void *ptr)
> +{
> +	const struct net_device *dev = ptr;
> +	struct net *net = dev_net(dev);
> +
> +	if (event == NETDEV_DOWN)
> +		nf_ct_iterate_cleanup(net, device_cmp,
> +				      (void *)(long)dev->ifindex);
> +
> +	return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block masq_dev_notifier = {
> +	.notifier_call	= masq_device_event,
> +};
> +
> +static int masq_inet_event(struct notifier_block *this,
> +			   unsigned long event, void *ptr)
> +{
> +	struct inet6_ifaddr *ifa = ptr;
> +
> +	return masq_device_event(this, event, ifa->idev->dev);
> +}
> +
> +static struct notifier_block masq_inet_notifier = {
> +	.notifier_call	= masq_inet_event,
> +};
> +
> +static struct xt_target masquerade_tg6_reg __read_mostly = {
> +	.name		= "MASQUERADE",
> +	.family		= NFPROTO_IPV6,
> +	.checkentry	= masquerade_tg6_checkentry,
> +	.target		= masquerade_tg6,
> +	.targetsize	= sizeof(struct nf_nat_range),
> +	.table		= "nat",
> +	.hooks		= 1 << NF_INET_POST_ROUTING,
> +	.me		= THIS_MODULE,
> +};
> +
> +static int __init masquerade_tg6_init(void)
> +{
> +	int err;
> +
> +	err = xt_register_target(&masquerade_tg6_reg);
> +	if (err == 0) {
> +		register_netdevice_notifier(&masq_dev_notifier);
> +		register_inet6addr_notifier(&masq_inet_notifier);
> +	}
> +
> +	return err;
> +}
> +static void __exit masquerade_tg6_exit(void)
> +{
> +	unregister_inet6addr_notifier(&masq_inet_notifier);
> +	unregister_netdevice_notifier(&masq_dev_notifier);
> +	xt_unregister_target(&masquerade_tg6_reg);
> +}
> +
> +module_init(masquerade_tg6_init);
> +module_exit(masquerade_tg6_exit);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Patrick McHardy <[email-masked]>");
> +MODULE_DESCRIPTION("Xtables: automatic address SNAT");
> -- 
> 1.7.1
> 
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