Subject: Re: [PATCH 1/1] bridge: Fix NAT66ed IPv6 packets not being bridged correctly

From: Pablo Neira Ayuso <[email-masked]>
Date: Fri, 3 Oct 2014 13:21:19 +0200

Hi Bernhard,

Sorry for taking a bit to get back to you with feedback. We've been
discussing recently some changes in br_netfilter. Basically, to
modularize it [1] and this has taken a while.

Regarding your change. Sven Eckelmann (CC'ed in this email) sent a RFC
out of the merge window that have remain tagged in my patchwork, you
can find it here.

http://patchwork.ozlabs.org/patch/381027/

I would like to see a submission that covers all NAT66 scenarios that
we currenty support.

Thanks.

[1] http://comments.gmane.org/gmane.comp.security.firewalls.netfilter.devel/54234

On Mon, Sep 15, 2014 at 05:40:09PM -0400, David Miller wrote:
> From: Bernhard Thaler <[email-masked]>
> Date: Mon, 15 Sep 2014 23:27:28 +0200
> 
> CC:'ing netfilter-devel and the netfilter maintainer, which is
> probably the primary place this patch should have been submitted.
> 
> > Ethernet frames are not bridged to correct interface when packets have
> > been NAT66ed; compared to IPv4 logic in code, IPv6 code does not store
> > original address (before NAT) on transmit to determine if packet was
> > NAT66ed on receive to swap addresses back.
> > 
> > Changes added in br_netfilter.c to store original address, compare
> > against it and determine correct output interface. Changes needed in
> > netfilter_bridge.h to store IPv6 address in pre-existing union.
> > Export of ip6_route_input needed to use it in br_netfilter.c.
> > 
> > Problem may only affect systems doing NAT66 and ethernet bridging at
> > the same time. Tested in NAT66 setup on base of an ethernet bridge.
> > 
> > Signed-off-by: Bernhard Thaler <[email-masked]>
> > ---
> >  include/linux/netfilter_bridge.h |    2 +
> >  net/bridge/br_netfilter.c        |  136 ++++++++++++++++++++++++++++----------
> >  net/ipv6/route.c                 |    1 +
> >  3 files changed, 105 insertions(+), 34 deletions(-)
> > 
> > diff --git a/include/linux/netfilter_bridge.h b/include/linux/netfilter_bridge.h
> > index 8ab1c27..3a9cdcd 100644
> > --- a/include/linux/netfilter_bridge.h
> > +++ b/include/linux/netfilter_bridge.h
> > @@ -2,6 +2,7 @@
> >  #define __LINUX_BRIDGE_NETFILTER_H
> >  
> >  #include <uapi/linux/netfilter_bridge.h>
> > +#include <uapi/linux/in6.h>
> >  
> >  
> >  enum nf_br_hook_priorities {
> > @@ -79,6 +80,7 @@ static inline unsigned int nf_bridge_pad(const struct sk_buff *skb)
> >  struct bridge_skb_cb {
> >  	union {
> >  		__be32 ipv4;
> > +		struct in6_addr ipv6;
> >  	} daddr;
> >  };
> >  
> > diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
> > index a615264..2ae3888 100644
> > --- a/net/bridge/br_netfilter.c
> > +++ b/net/bridge/br_netfilter.c
> > @@ -35,6 +35,9 @@
> >  #include <net/ip.h>
> >  #include <net/ipv6.h>
> >  #include <net/route.h>
> > +#include <net/ip6_route.h>
> > +#include <net/flow.h>
> > +#include <net/dst.h>
> >  
> >  #include <asm/uaccess.h>
> >  #include "br_private.h"
> > @@ -42,10 +45,18 @@
> >  #include <linux/sysctl.h>
> >  #endif
> >  
> > -#define skb_origaddr(skb)	 (((struct bridge_skb_cb *) \
> > -				 (skb->nf_bridge->data))->daddr.ipv4)
> > -#define store_orig_dstaddr(skb)	 (skb_origaddr(skb) = ip_hdr(skb)->daddr)
> > -#define dnat_took_place(skb)	 (skb_origaddr(skb) != ip_hdr(skb)->daddr)
> > +#define skb_origaddr(skb)		(((struct bridge_skb_cb *)\
> > +					(skb->nf_bridge->data))->daddr.ipv4)
> > +#define skb_origaddr_ipv6(skb)		(((struct bridge_skb_cb *)\
> > +					(skb->nf_bridge->data))->daddr.ipv6)
> > +#define store_orig_dstaddr(skb)		(skb_origaddr(skb) = ip_hdr(skb)->daddr)
> > +#define store_orig_dstaddr_ipv6(skb)	(skb_origaddr_ipv6(skb) = \
> > +					ipv6_hdr(skb)->daddr)
> > +#define dnat_took_place(skb)		(skb_origaddr(skb) != \
> > +					ip_hdr(skb)->daddr)
> > +#define dnat_took_place_ipv6(skb)	(memcmp(&skb_origaddr_ipv6(skb), \
> > +					&(ipv6_hdr(skb)->daddr), \
> > +					sizeof(struct in6_addr)) != 0)
> >  
> >  #ifdef CONFIG_SYSCTL
> >  static struct ctl_table_header *brnf_sysctl_header;
> > @@ -340,36 +351,6 @@ int nf_bridge_copy_header(struct sk_buff *skb)
> >  	return 0;
> >  }
> >  
> > -/* PF_BRIDGE/PRE_ROUTING *********************************************/
> > -/* Undo the changes made for ip6tables PREROUTING and continue the
> > - * bridge PRE_ROUTING hook. */
> > -static int br_nf_pre_routing_finish_ipv6(struct sk_buff *skb)
> > -{
> > -	struct nf_bridge_info *nf_bridge = skb->nf_bridge;
> > -	struct rtable *rt;
> > -
> > -	if (nf_bridge->mask & BRNF_PKT_TYPE) {
> > -		skb->pkt_type = PACKET_OTHERHOST;
> > -		nf_bridge->mask ^= BRNF_PKT_TYPE;
> > -	}
> > -	nf_bridge->mask ^= BRNF_NF_BRIDGE_PREROUTING;
> > -
> > -	rt = bridge_parent_rtable(nf_bridge->physindev);
> > -	if (!rt) {
> > -		kfree_skb(skb);
> > -		return 0;
> > -	}
> > -	skb_dst_set_noref(skb, &rt->dst);
> > -
> > -	skb->dev = nf_bridge->physindev;
> > -	nf_bridge_update_protocol(skb);
> > -	nf_bridge_push_encap_header(skb);
> > -	NF_HOOK_THRESH(NFPROTO_BRIDGE, NF_BR_PRE_ROUTING, skb, skb->dev, NULL,
> > -		       br_handle_frame_finish, 1);
> > -
> > -	return 0;
> > -}
> > -
> >  /* Obtain the correct destination MAC address, while preserving the original
> >   * source MAC address. If we already know this address, we just copy it. If we
> >   * don't, we use the neighbour framework to find out. In both cases, we make
> > @@ -527,6 +508,92 @@ bridged_dnat:
> >  	return 0;
> >  }
> >  
> > +/* PF_BRIDGE/PRE_ROUTING *********************************************
> > + * Undo the changes made for ip6tables PREROUTING and continue the
> > + * bridge PRE_ROUTING hook.
> > + */
> > +static int br_nf_pre_routing_finish_ipv6(struct sk_buff *skb)
> > +{
> > +	struct net_device *dev = skb->dev;
> > +	struct ipv6hdr *iph = ipv6_hdr(skb);
> > +	struct nf_bridge_info *nf_bridge = skb->nf_bridge;
> > +	struct rtable *rt;
> > +	struct dst_entry *dst;
> > +	struct flowi6 fl6 = {
> > +		.flowi6_iif = skb->dev->ifindex,
> > +		.daddr = iph->daddr,
> > +		.saddr = iph->saddr,
> > +		.flowlabel = ip6_flowinfo(iph),
> > +		.flowi6_mark = skb->mark,
> > +		.flowi6_proto = iph->nexthdr,
> > +	};
> > +
> > +	if (nf_bridge->mask & BRNF_PKT_TYPE) {
> > +		skb->pkt_type = PACKET_OTHERHOST;
> > +		nf_bridge->mask ^= BRNF_PKT_TYPE;
> > +	}
> > +	nf_bridge->mask ^= BRNF_NF_BRIDGE_PREROUTING;
> > +
> > +	if (dnat_took_place_ipv6(skb)) {
> > +		ip6_route_input(skb);
> > +		/* ip6_route_input is void function,
> > +		 * no int returned as in ip4_route_input
> > +		 * changes value of skb->_skb_refdst) on success
> > +		 */
> > +		if (skb->_skb_refdst == 0) {
> > +			struct in_device *in_dev = __in_dev_get_rcu(dev);
> > +
> > +			if (!in_dev || IN_DEV_FORWARD(in_dev))
> > +				goto free_skb;
> > +
> > +			dst = ip6_route_output(dev_net(dev), skb->sk, &fl6);
> > +			if (!IS_ERR(dst)) {
> > +				/* - Bridged-and-DNAT'ed traffic doesn't
> > +				 *   require ip_forwarding.
> > +				 */
> > +				if (dst->dev == dev) {
> > +					skb_dst_set(skb, dst);
> > +					goto bridged_dnat;
> > +				}
> > +				dst_release(dst);
> > +			}
> > +free_skb:
> > +			kfree_skb(skb);
> > +			return 0;
> > +		} else {
> > +			if (skb_dst(skb)->dev == dev) {
> > +bridged_dnat:
> > +				skb->dev = nf_bridge->physindev;
> > +				nf_bridge_update_protocol(skb);
> > +				nf_bridge_push_encap_header(skb);
> > +				NF_HOOK_THRESH(NFPROTO_BRIDGE,
> > +					       NF_BR_PRE_ROUTING,
> > +					       skb, skb->dev, NULL,
> > +					       br_nf_pre_routing_finish_bridge,
> > +					       1);
> > +				return 0;
> > +			}
> > +			memcpy(eth_hdr(skb)->h_dest, dev->dev_addr, ETH_ALEN);
> > +			skb->pkt_type = PACKET_HOST;
> > +		}
> > +	} else {
> > +		rt = bridge_parent_rtable(nf_bridge->physindev);
> > +		if (!rt) {
> > +			kfree_skb(skb);
> > +			return 0;
> > +		}
> > +		skb_dst_set_noref(skb, &rt->dst);
> > +	}
> > +
> > +	skb->dev = nf_bridge->physindev;
> > +	nf_bridge_update_protocol(skb);
> > +	nf_bridge_push_encap_header(skb);
> > +	NF_HOOK_THRESH(NFPROTO_BRIDGE, NF_BR_PRE_ROUTING, skb, skb->dev, NULL,
> > +		       br_handle_frame_finish, 1);
> > +
> > +	return 0;
> > +}
> > +
> >  static struct net_device *brnf_get_logical_dev(struct sk_buff *skb, const struct net_device *dev)
> >  {
> >  	struct net_device *vlan, *br;
> > @@ -658,6 +725,7 @@ static unsigned int br_nf_pre_routing_ipv6(const struct nf_hook_ops *ops,
> >  	if (!setup_pre_routing(skb))
> >  		return NF_DROP;
> >  
> > +	store_orig_dstaddr_ipv6(skb);
> >  	skb->protocol = htons(ETH_P_IPV6);
> >  	NF_HOOK(NFPROTO_IPV6, NF_INET_PRE_ROUTING, skb, skb->dev, NULL,
> >  		br_nf_pre_routing_finish_ipv6);
> > diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> > index f23fbd2..e328905 100644
> > --- a/net/ipv6/route.c
> > +++ b/net/ipv6/route.c
> > @@ -1017,6 +1017,7 @@ void ip6_route_input(struct sk_buff *skb)
> >  
> >  	skb_dst_set(skb, ip6_route_input_lookup(net, skb->dev, &fl6, flags));
> >  }
> > +EXPORT_SYMBOL(ip6_route_input);
> >  
> >  static struct rt6_info *ip6_pol_route_output(struct net *net, struct fib6_table *table,
> >  					     struct flowi6 *fl6, int flags)
> > -- 
> > 1.7.10.4
> >