Hi Bernhard,
Florian Westphal is currently exploring alternative solutions so
br_netfilter can stop (ab)using the layer 3 infrastructure from the
bridge code (this layering violation has been causing problems for
quite some time, eg. some users don't expect a bridge to modify alter
the fragmented traffic).
Although IPv6 support in br_netfilter is fairly incomplete, let me put
these patches in a hold until Florian comes back to us with some
feedback, we'll integrate them in some way or another at some point.
Thanks for your work and patience so far.
On Wed, Mar 18, 2015 at 10:52:11PM +0100, Bernhard Thaler wrote:
> IPv4 allows to redirect any traffic over a bridge to the local machine using
> iptables.
>
> $ sysctl -w net.bridge.bridge-nf-call-iptables=1
> $ iptables -t nat -A PREROUTING -p tcp -m tcp --dport 8080 \
> -j REDIRECT --to-ports 81
>
> This didn't work with ip6tables because the redirect was not correctly detected.
> The bridge pre-routing (finish) netfilter hook has to check for a possible
> redirect and then fix the destination mac address. This makes it possible to
> use the ip6tables rules for local DNAT REDIRECT similar to the IPv4 version.
>
> $ sysctl -w net.bridge.bridge-nf-call-ip6tables=1
> $ ip6tables -t nat -A PREROUTING -p tcp -m tcp --dport 8080 \
> -j REDIRECT --to-ports 81
>
> Signed-off-by: Sven Eckelmann <sven@xxxxxxxxxxxxx>
> [bernhard.thaler@xxxxxxxx: rebased, adjust function order]
> [bernhard.thaler@xxxxxxxx: rebased, add indirect call to ip6_route_input]
> Signed-off-by: Bernhard Thaler <bernhard.thaler@xxxxxxxx>
> ---
> Patch revision history:
>
> v2
> * re-base again to davem's current net-next
> * add indirect call to ip6_route_input via nf_ipv6_ops to avoid
> direct dependency to ipv6.ko just because of function calls
>
> v1
> * rebase "bridge: Allow to redirect IPv6 traffic to local machine"
> to davem's current net-next
> * adjust function order to avoid prototype for br_nf_pre_routing_finish_bridge
>
> (v0)
> * originally there were two patches solving this problem
> * Patch from Sven Eckelmann was chosen to base solution on
> see: bridge: Allow to redirect IPv6 traffic to local machine
> see: bridge: Fix NAT66ed IPv6 packets not being bridged correctly
>
> include/linux/netfilter_bridge.h | 2 +
> include/linux/netfilter_ipv6.h | 1 +
> net/bridge/br_netfilter.c | 128 +++++++++++++++++++++++++++++---------
> net/ipv6/netfilter.c | 1 +
> 4 files changed, 102 insertions(+), 30 deletions(-)
>
> diff --git a/include/linux/netfilter_bridge.h b/include/linux/netfilter_bridge.h
> index bb39113..419f3db 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 {
> @@ -57,6 +58,7 @@ 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/include/linux/netfilter_ipv6.h b/include/linux/netfilter_ipv6.h
> index 64dad1cc..e2d1969 100644
> --- a/include/linux/netfilter_ipv6.h
> +++ b/include/linux/netfilter_ipv6.h
> @@ -25,6 +25,7 @@ void ipv6_netfilter_fini(void);
> struct nf_ipv6_ops {
> int (*chk_addr)(struct net *net, const struct in6_addr *addr,
> const struct net_device *dev, int strict);
> + void (*route_input)(struct sk_buff *skb);
> };
>
> extern const struct nf_ipv6_ops __rcu *nf_ipv6_ops;
> diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
> index b260a97..775d638 100644
> --- a/net/bridge/br_netfilter.c
> +++ b/net/bridge/br_netfilter.c
> @@ -45,8 +45,14 @@
>
> #define skb_origaddr(skb) (((struct bridge_skb_cb *) \
> (skb->nf_bridge->data))->daddr.ipv4)
> +#define skb_origaddr6(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_dstaddr6(skb) (skb_origaddr6(skb) = ipv6_hdr(skb)->daddr)
> #define dnat_took_place(skb) (skb_origaddr(skb) != ip_hdr(skb)->daddr)
> +#define dnat_took_place6(skb) (memcmp(&skb_origaddr6(skb), \
> + &ipv6_hdr(skb)->daddr, \
> + sizeof(ipv6_hdr(skb)->daddr)) != 0)
>
> #ifdef CONFIG_SYSCTL
> static struct ctl_table_header *brnf_sysctl_header;
> @@ -247,36 +253,6 @@ static void nf_bridge_update_protocol(struct sk_buff *skb)
> skb->protocol = htons(ETH_P_PPP_SES);
> }
>
> -/* 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
> @@ -322,6 +298,97 @@ free_skb:
> return 0;
> }
>
> +/* PF_BRIDGE/PRE_ROUTING *********************************************/
> +/* Undo the changes made for ip6tables PREROUTING and continue the
> + * bridge PRE_ROUTING hook.
> + */
> +
> +/* This requires some explaining. If DNAT has taken place,
> + * we will need to fix up the destination Ethernet address.
> + *
> + * There are two cases to consider:
> + * 1. The packet was DNAT'ed to a device in the same bridge
> + * port group as it was received on. We can still bridge
> + * the packet.
> + * 2. The packet was DNAT'ed to a different device, either
> + * a non-bridged device or another bridge port group.
> + * The packet will need to be routed.
> + *
> + * The correct way of distinguishing between these two cases is to
> + * call ip6_route_input() and to look at skb->dst->dev, which is
> + * changed to the destination device if ip6_route_input() succeeds.
> + * ip6_route_input() is called indirectly via v6ops->route_input to
> + * avoid direct dependency to ipv6.ko due to function calls.
> + *
> + * Let's first consider the case that ip6_route_input() succeeds:
> + *
> + * If the output device equals the logical bridge device the packet
> + * came in on, we can consider this bridging. The corresponding MAC
> + * address will be obtained in br_nf_pre_routing_finish_bridge.
> + * Otherwise, the packet is considered to be routed and we just
> + * change the destination MAC address so that the packet will
> + * later be passed up to the IP stack to be routed. For a redirected
> + * packet, ip6_route_input() will give back the localhost as output device,
> + * which differs from the bridge device.
> + *
> + * Let's now consider the case that ip6_route_input() fails:
> + *
> + * This can be because the destination address is martian, in which case
> + * the packet will be dropped.
> + */
> +static int br_nf_pre_routing_finish_ipv6(struct sk_buff *skb)
> +{
> + struct nf_bridge_info *nf_bridge = skb->nf_bridge;
> + struct rtable *rt;
> + struct net_device *dev = skb->dev;
> + const struct nf_ipv6_ops *v6ops = nf_get_ipv6_ops();
> +
> + 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_place6(skb)) {
> + skb_dst_drop(skb);
> + v6ops->route_input(skb);
> +
> + if (skb_dst(skb)->error) {
> + kfree_skb(skb);
> + return 0;
> + }
> +
> + if (skb_dst(skb)->dev == dev) {
> + 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;
> +}
> +
> /* This requires some explaining. If DNAT has taken place,
> * we will need to fix up the destination Ethernet address.
> *
> @@ -570,6 +637,7 @@ static unsigned int br_nf_pre_routing_ipv6(const struct nf_hook_ops *ops,
> if (!setup_pre_routing(skb))
> return NF_DROP;
>
> + store_orig_dstaddr6(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/netfilter.c b/net/ipv6/netfilter.c
> index 398377a..0cd8ec9 100644
> --- a/net/ipv6/netfilter.c
> +++ b/net/ipv6/netfilter.c
> @@ -191,6 +191,7 @@ static __sum16 nf_ip6_checksum_partial(struct sk_buff *skb, unsigned int hook,
>
> static const struct nf_ipv6_ops ipv6ops = {
> .chk_addr = ipv6_chk_addr,
> + .route_input = ip6_route_input
> };
>
> static const struct nf_afinfo nf_ip6_afinfo = {
> --
> 1.7.10.4
>
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