netfilter: flow table support for IPv6

This patch adds the IPv6 flow table type, that implements the datapath
flow table to forward IPv6 traffic.

This patch exports ip6_dst_mtu_forward() that is required to check for
mtu to pass up packets that need PMTUD handling to the classic
forwarding path.
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

include/net/ipv6.h

@@ -969,6 +969,8 @@ static inline struct sk_buff *ip6_finish_skb(struct sock *sk)
 			      &inet6_sk(sk)->cork);
 }
 
+unsigned int ip6_dst_mtu_forward(const struct dst_entry *dst);
+
 int ip6_dst_lookup(struct net *net, struct sock *sk, struct dst_entry **dst,
 		   struct flowi6 *fl6);
 struct dst_entry *ip6_dst_lookup_flow(const struct sock *sk, struct flowi6 *fl6,

net/ipv6/ip6_output.c

@@ -378,7 +378,7 @@ static inline int ip6_forward_finish(struct net *net, struct sock *sk,
 	return dst_output(net, sk, skb);
 }
 
-static unsigned int ip6_dst_mtu_forward(const struct dst_entry *dst)
+unsigned int ip6_dst_mtu_forward(const struct dst_entry *dst)
 {
 	unsigned int mtu;
 	struct inet6_dev *idev;
@@ -398,6 +398,7 @@ static unsigned int ip6_dst_mtu_forward(const struct dst_entry *dst)
 
 	return mtu;
 }
+EXPORT_SYMBOL_GPL(ip6_dst_mtu_forward);
 
 static bool ip6_pkt_too_big(const struct sk_buff *skb, unsigned int mtu)
 {

net/ipv6/netfilter/Kconfig

@@ -71,6 +71,14 @@ config NFT_FIB_IPV6
 endif # NF_TABLES_IPV6
 endif # NF_TABLES
 
+config NF_FLOW_TABLE_IPV6
+	select NF_FLOW_TABLE
+	tristate "Netfilter flow table IPv6 module"
+	help
+	  This option adds the flow table IPv6 support.
+
+	  To compile it as a module, choose M here.
+
 config NF_DUP_IPV6
 	tristate "Netfilter IPv6 packet duplication to alternate destination"
 	depends on !NF_CONNTRACK || NF_CONNTRACK

net/ipv6/netfilter/Makefile

@@ -45,6 +45,9 @@ obj-$(CONFIG_NFT_REDIR_IPV6) += nft_redir_ipv6.o
 obj-$(CONFIG_NFT_DUP_IPV6) += nft_dup_ipv6.o
 obj-$(CONFIG_NFT_FIB_IPV6) += nft_fib_ipv6.o
 
+# flow table support
+obj-$(CONFIG_NF_FLOW_TABLE_IPV6) += nf_flow_table_ipv6.o
+
 # matches
 obj-$(CONFIG_IP6_NF_MATCH_AH) += ip6t_ah.o
 obj-$(CONFIG_IP6_NF_MATCH_EUI64) += ip6t_eui64.o

net/ipv6/netfilter/nf_flow_table_ipv6.c

+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/netfilter.h>
+#include <linux/rhashtable.h>
+#include <linux/ipv6.h>
+#include <linux/netdevice.h>
+#include <linux/ipv6.h>
+#include <net/ipv6.h>
+#include <net/ip6_route.h>
+#include <net/neighbour.h>
+#include <net/netfilter/nf_flow_table.h>
+#include <net/netfilter/nf_tables.h>
+/* For layer 4 checksum field offset. */
+#include <linux/tcp.h>
+#include <linux/udp.h>
+
+static int nf_flow_nat_ipv6_tcp(struct sk_buff *skb, unsigned int thoff,
+				struct in6_addr *addr,
+				struct in6_addr *new_addr)
+{
+	struct tcphdr *tcph;
+
+	if (!pskb_may_pull(skb, thoff + sizeof(*tcph)) ||
+	    skb_try_make_writable(skb, thoff + sizeof(*tcph)))
+		return -1;
+
+	tcph = (void *)(skb_network_header(skb) + thoff);
+	inet_proto_csum_replace16(&tcph->check, skb, addr->s6_addr32,
+				  new_addr->s6_addr32, true);
+
+	return 0;
+}
+
+static int nf_flow_nat_ipv6_udp(struct sk_buff *skb, unsigned int thoff,
+				struct in6_addr *addr,
+				struct in6_addr *new_addr)
+{
+	struct udphdr *udph;
+
+	if (!pskb_may_pull(skb, thoff + sizeof(*udph)) ||
+	    skb_try_make_writable(skb, thoff + sizeof(*udph)))
+		return -1;
+
+	udph = (void *)(skb_network_header(skb) + thoff);
+	if (udph->check || skb->ip_summed == CHECKSUM_PARTIAL) {
+		inet_proto_csum_replace16(&udph->check, skb, addr->s6_addr32,
+					  new_addr->s6_addr32, true);
+		if (!udph->check)
+			udph->check = CSUM_MANGLED_0;
+	}
+
+	return 0;
+}
+
+static int nf_flow_nat_ipv6_l4proto(struct sk_buff *skb, struct ipv6hdr *ip6h,
+				    unsigned int thoff, struct in6_addr *addr,
+				    struct in6_addr *new_addr)
+{
+	switch (ip6h->nexthdr) {
+	case IPPROTO_TCP:
+		if (nf_flow_nat_ipv6_tcp(skb, thoff, addr, new_addr) < 0)
+			return NF_DROP;
+		break;
+	case IPPROTO_UDP:
+		if (nf_flow_nat_ipv6_udp(skb, thoff, addr, new_addr) < 0)
+			return NF_DROP;
+		break;
+	}
+
+	return 0;
+}
+
+static int nf_flow_snat_ipv6(const struct flow_offload *flow,
+			     struct sk_buff *skb, struct ipv6hdr *ip6h,
+			     unsigned int thoff,
+			     enum flow_offload_tuple_dir dir)
+{
+	struct in6_addr addr, new_addr;
+
+	switch (dir) {
+	case FLOW_OFFLOAD_DIR_ORIGINAL:
+		addr = ip6h->saddr;
+		new_addr = flow->tuplehash[FLOW_OFFLOAD_DIR_REPLY].tuple.dst_v6;
+		ip6h->saddr = new_addr;
+		break;
+	case FLOW_OFFLOAD_DIR_REPLY:
+		addr = ip6h->daddr;
+		new_addr = flow->tuplehash[FLOW_OFFLOAD_DIR_ORIGINAL].tuple.src_v6;
+		ip6h->daddr = new_addr;
+		break;
+	default:
+		return -1;
+	}
+
+	return nf_flow_nat_ipv6_l4proto(skb, ip6h, thoff, &addr, &new_addr);
+}
+
+static int nf_flow_dnat_ipv6(const struct flow_offload *flow,
+			     struct sk_buff *skb, struct ipv6hdr *ip6h,
+			     unsigned int thoff,
+			     enum flow_offload_tuple_dir dir)
+{
+	struct in6_addr addr, new_addr;
+
+	switch (dir) {
+	case FLOW_OFFLOAD_DIR_ORIGINAL:
+		addr = ip6h->daddr;
+		new_addr = flow->tuplehash[FLOW_OFFLOAD_DIR_REPLY].tuple.src_v6;
+		ip6h->daddr = new_addr;
+		break;
+	case FLOW_OFFLOAD_DIR_REPLY:
+		addr = ip6h->saddr;
+		new_addr = flow->tuplehash[FLOW_OFFLOAD_DIR_ORIGINAL].tuple.dst_v6;
+		ip6h->saddr = new_addr;
+		break;
+	default:
+		return -1;
+	}
+
+	return nf_flow_nat_ipv6_l4proto(skb, ip6h, thoff, &addr, &new_addr);
+}
+
+static int nf_flow_nat_ipv6(const struct flow_offload *flow,
+			    struct sk_buff *skb,
+			    enum flow_offload_tuple_dir dir)
+{
+	struct ipv6hdr *ip6h = ipv6_hdr(skb);
+	unsigned int thoff = sizeof(*ip6h);
+
+	if (flow->flags & FLOW_OFFLOAD_SNAT &&
+	    (nf_flow_snat_port(flow, skb, thoff, ip6h->nexthdr, dir) < 0 ||
+	     nf_flow_snat_ipv6(flow, skb, ip6h, thoff, dir) < 0))
+		return -1;
+	if (flow->flags & FLOW_OFFLOAD_DNAT &&
+	    (nf_flow_dnat_port(flow, skb, thoff, ip6h->nexthdr, dir) < 0 ||
+	     nf_flow_dnat_ipv6(flow, skb, ip6h, thoff, dir) < 0))
+		return -1;
+
+	return 0;
+}
+
+static int nf_flow_tuple_ipv6(struct sk_buff *skb, const struct net_device *dev,
+			      struct flow_offload_tuple *tuple)
+{
+	struct flow_ports *ports;
+	struct ipv6hdr *ip6h;
+	unsigned int thoff;
+
+	if (!pskb_may_pull(skb, sizeof(*ip6h)))
+		return -1;
+
+	ip6h = ipv6_hdr(skb);
+
+	if (ip6h->nexthdr != IPPROTO_TCP &&
+	    ip6h->nexthdr != IPPROTO_UDP)
+		return -1;
+
+	thoff = sizeof(*ip6h);
+	if (!pskb_may_pull(skb, thoff + sizeof(*ports)))
+		return -1;
+
+	ports = (struct flow_ports *)(skb_network_header(skb) + thoff);
+
+	tuple->src_v6		= ip6h->saddr;
+	tuple->dst_v6		= ip6h->daddr;
+	tuple->src_port		= ports->source;
+	tuple->dst_port		= ports->dest;
+	tuple->l3proto		= AF_INET6;
+	tuple->l4proto		= ip6h->nexthdr;
+	tuple->iifidx		= dev->ifindex;
+
+	return 0;
+}
+
+/* Based on ip_exceeds_mtu(). */
+static bool __nf_flow_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu)
+{
+	if (skb->len <= mtu)
+		return false;
+
+	if (skb_is_gso(skb) && skb_gso_validate_mtu(skb, mtu))
+		return false;
+
+	return true;
+}
+
+static bool nf_flow_exceeds_mtu(struct sk_buff *skb, const struct rt6_info *rt)
+{
+	u32 mtu;
+
+	mtu = ip6_dst_mtu_forward(&rt->dst);
+	if (__nf_flow_exceeds_mtu(skb, mtu))
+		return true;
+
+	return false;
+}
+
+static unsigned int
+nf_flow_offload_ipv6_hook(void *priv, struct sk_buff *skb,
+			  const struct nf_hook_state *state)
+{
+	struct flow_offload_tuple_rhash *tuplehash;
+	struct nf_flowtable *flow_table = priv;
+	struct flow_offload_tuple tuple = {};
+	enum flow_offload_tuple_dir dir;
+	struct flow_offload *flow;
+	struct net_device *outdev;
+	struct in6_addr *nexthop;
+	struct ipv6hdr *ip6h;
+	struct rt6_info *rt;
+
+	if (skb->protocol != htons(ETH_P_IPV6))
+		return NF_ACCEPT;
+
+	if (nf_flow_tuple_ipv6(skb, state->in, &tuple) < 0)
+		return NF_ACCEPT;
+
+	tuplehash = flow_offload_lookup(flow_table, &tuple);
+	if (tuplehash == NULL)
+		return NF_ACCEPT;
+
+	outdev = dev_get_by_index_rcu(state->net, tuplehash->tuple.oifidx);
+	if (!outdev)
+		return NF_ACCEPT;
+
+	dir = tuplehash->tuple.dir;
+	flow = container_of(tuplehash, struct flow_offload, tuplehash[dir]);
+
+	rt = (struct rt6_info *)flow->tuplehash[dir].tuple.dst_cache;
+	if (unlikely(nf_flow_exceeds_mtu(skb, rt)))
+		return NF_ACCEPT;
+
+	if (skb_try_make_writable(skb, sizeof(*ip6h)))
+		return NF_DROP;
+
+	if (flow->flags & (FLOW_OFFLOAD_SNAT | FLOW_OFFLOAD_DNAT) &&
+	    nf_flow_nat_ipv6(flow, skb, dir) < 0)
+		return NF_DROP;
+
+	flow->timeout = (u32)jiffies + NF_FLOW_TIMEOUT;
+	ip6h = ipv6_hdr(skb);
+	ip6h->hop_limit--;
+
+	skb->dev = outdev;
+	nexthop = rt6_nexthop(rt, &flow->tuplehash[!dir].tuple.src_v6);
+	neigh_xmit(NEIGH_ND_TABLE, outdev, nexthop, skb);
+
+	return NF_STOLEN;
+}
+
+static struct nf_flowtable_type flowtable_ipv6 = {
+	.family		= NFPROTO_IPV6,
+	.params		= &nf_flow_offload_rhash_params,
+	.gc		= nf_flow_offload_work_gc,
+	.hook		= nf_flow_offload_ipv6_hook,
+	.owner		= THIS_MODULE,
+};
+
+static int __init nf_flow_ipv6_module_init(void)
+{
+	nft_register_flowtable_type(&flowtable_ipv6);
+
+	return 0;
+}
+
+static void __exit nf_flow_ipv6_module_exit(void)
+{
+	nft_unregister_flowtable_type(&flowtable_ipv6);
+}
+
+module_init(nf_flow_ipv6_module_init);
+module_exit(nf_flow_ipv6_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
+MODULE_ALIAS_NF_FLOWTABLE(AF_INET6);