Sven Eckelmann
2014-Aug-18 14:36 UTC
[Bridge] [RFC] bridge: Allow to redirect IPv6 traffic to local machine
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 at open-mesh.com>
---
Hi Artie Hamilton,
I just had the same problem and modified br_netfilter.c to work in a similar
setup. Maybe this is also helps you.
I've used your example in the patch description because it was simple and
easy.
Kind regards,
Sven
include/linux/netfilter_bridge.h | 2 +
net/bridge/br_netfilter.c | 80 +++++++++++++++++++++++++++++++++++++---
net/ipv6/route.c | 1 +
3 files changed, 78 insertions(+), 5 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..ef8c0ac 100644
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -18,6 +18,7 @@
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/ip.h>
+#include <linux/ipv6.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/if_arp.h>
@@ -30,11 +31,13 @@
#include <linux/netfilter_ipv6.h>
#include <linux/netfilter_arp.h>
#include <linux/in_route.h>
+#include <linux/ipv6_route.h>
#include <linux/inetdevice.h>
#include <net/ip.h>
#include <net/ipv6.h>
#include <net/route.h>
+#include <net/ip6_route.h>
#include <asm/uaccess.h>
#include "br_private.h"
@@ -47,6 +50,13 @@
#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_origaddr6(skb) (((struct bridge_skb_cb *) \
+ (skb->nf_bridge->data))->daddr.ipv6)
+#define store_orig_dstaddr6(skb) (skb_origaddr6(skb) = ipv6_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;
static int brnf_call_iptables __read_mostly = 1;
@@ -343,10 +353,45 @@ int nf_bridge_copy_header(struct sk_buff *skb)
/* 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_bridge(struct sk_buff *skb);
+
+/* 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.
+ *
+ * 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;
if (nf_bridge->mask & BRNF_PKT_TYPE) {
skb->pkt_type = PACKET_OTHERHOST;
@@ -354,12 +399,36 @@ static int br_nf_pre_routing_finish_ipv6(struct sk_buff
*skb)
}
nf_bridge->mask ^= BRNF_NF_BRIDGE_PREROUTING;
- rt = bridge_parent_rtable(nf_bridge->physindev);
- if (!rt) {
- kfree_skb(skb);
- return 0;
+ if (dnat_took_place6(skb)) {
+ skb_dst_drop(skb);
+ ip6_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_dst_set_noref(skb, &rt->dst);
skb->dev = nf_bridge->physindev;
nf_bridge_update_protocol(skb);
@@ -658,6 +727,7 @@ 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/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)
--
2.1.0