Commit 97add9f0 authored by Pablo Neira Ayuso's avatar Pablo Neira Ayuso
Browse files

netfilter: flow table support for IPv4 



This patch adds the IPv4 flow table type, that implements the datapath
flow table to forward IPv4 traffic. Rationale is:

1) Look up for the packet in the flow table, from the ingress hook.
2) If there's a hit, decrement ttl and pass it on to the neighbour layer
   for transmission.
3) If there's a miss, packet is passed up to the classic forwarding
   path.

This patch also supports layer 3 source and destination NAT.

Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent ac2a6666

net/ipv4/netfilter/Kconfig

+8 −0
Original line number Diff line number Diff line
@@ -78,6 +78,14 @@ config NF_TABLES_ARP 


endif # NF_TABLES



config NF_FLOW_TABLE_IPV4

	select NF_FLOW_TABLE

	tristate "Netfilter flow table IPv4 module"

	help

	  This option adds the flow table IPv4 support.



	  To compile it as a module, choose M here.



config NF_DUP_IPV4

	tristate "Netfilter IPv4 packet duplication to alternate destination"

	depends on !NF_CONNTRACK || NF_CONNTRACK

net/ipv4/netfilter/Makefile

+3 −0
Original line number Diff line number Diff line
@@ -43,6 +43,9 @@ obj-$(CONFIG_NFT_REDIR_IPV4) += nft_redir_ipv4.o 
obj-$(CONFIG_NFT_DUP_IPV4) += nft_dup_ipv4.o

obj-$(CONFIG_NF_TABLES_ARP) += nf_tables_arp.o



# flow table support

obj-$(CONFIG_NF_FLOW_TABLE_IPV4) += nf_flow_table_ipv4.o



# generic IP tables 

obj-$(CONFIG_IP_NF_IPTABLES) += ip_tables.o

net/ipv4/netfilter/nf_flow_table_ipv4.c

0 → 100644
+283 −0
Original line number Diff line number Diff line 
#include <linux/kernel.h>

#include <linux/init.h>

#include <linux/module.h>

#include <linux/netfilter.h>

#include <linux/rhashtable.h>

#include <linux/ip.h>

#include <linux/netdevice.h>

#include <net/ip.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_ip_tcp(struct sk_buff *skb, unsigned int thoff,

			      __be32 addr, __be32 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_replace4(&tcph->check, skb, addr, new_addr, true);



	return 0;

}



static int nf_flow_nat_ip_udp(struct sk_buff *skb, unsigned int thoff,

			      __be32 addr, __be32 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_replace4(&udph->check, skb, addr,

					 new_addr, true);

		if (!udph->check)

			udph->check = CSUM_MANGLED_0;

	}



	return 0;

}



static int nf_flow_nat_ip_l4proto(struct sk_buff *skb, struct iphdr *iph,

				  unsigned int thoff, __be32 addr,

				  __be32 new_addr)

{

	switch (iph->protocol) {

	case IPPROTO_TCP:

		if (nf_flow_nat_ip_tcp(skb, thoff, addr, new_addr) < 0)

			return NF_DROP;

		break;

	case IPPROTO_UDP:

		if (nf_flow_nat_ip_udp(skb, thoff, addr, new_addr) < 0)

			return NF_DROP;

		break;

	}



	return 0;

}



static int nf_flow_snat_ip(const struct flow_offload *flow, struct sk_buff *skb,

			   struct iphdr *iph, unsigned int thoff,

			   enum flow_offload_tuple_dir dir)

{

	__be32 addr, new_addr;



	switch (dir) {

	case FLOW_OFFLOAD_DIR_ORIGINAL:

		addr = iph->saddr;

		new_addr = flow->tuplehash[FLOW_OFFLOAD_DIR_REPLY].tuple.dst_v4.s_addr;

		iph->saddr = new_addr;

		break;

	case FLOW_OFFLOAD_DIR_REPLY:

		addr = iph->daddr;

		new_addr = flow->tuplehash[FLOW_OFFLOAD_DIR_ORIGINAL].tuple.src_v4.s_addr;

		iph->daddr = new_addr;

		break;

	default:

		return -1;

	}

	csum_replace4(&iph->check, addr, new_addr);



	return nf_flow_nat_ip_l4proto(skb, iph, thoff, addr, new_addr);

}



static int nf_flow_dnat_ip(const struct flow_offload *flow, struct sk_buff *skb,

			   struct iphdr *iph, unsigned int thoff,

			   enum flow_offload_tuple_dir dir)

{

	__be32 addr, new_addr;



	switch (dir) {

	case FLOW_OFFLOAD_DIR_ORIGINAL:

		addr = iph->daddr;

		new_addr = flow->tuplehash[FLOW_OFFLOAD_DIR_REPLY].tuple.src_v4.s_addr;

		iph->daddr = new_addr;

		break;

	case FLOW_OFFLOAD_DIR_REPLY:

		addr = iph->saddr;

		new_addr = flow->tuplehash[FLOW_OFFLOAD_DIR_ORIGINAL].tuple.dst_v4.s_addr;

		iph->saddr = new_addr;

		break;

	default:

		return -1;

	}



	return nf_flow_nat_ip_l4proto(skb, iph, thoff, addr, new_addr);

}



static int nf_flow_nat_ip(const struct flow_offload *flow, struct sk_buff *skb,

			  enum flow_offload_tuple_dir dir)

{

	struct iphdr *iph = ip_hdr(skb);

	unsigned int thoff = iph->ihl * 4;



	if (flow->flags & FLOW_OFFLOAD_SNAT &&

	    (nf_flow_snat_port(flow, skb, thoff, iph->protocol, dir) < 0 ||

	     nf_flow_snat_ip(flow, skb, iph, thoff, dir) < 0))

		return -1;

	if (flow->flags & FLOW_OFFLOAD_DNAT &&

	    (nf_flow_dnat_port(flow, skb, thoff, iph->protocol, dir) < 0 ||

	     nf_flow_dnat_ip(flow, skb, iph, thoff, dir) < 0))

		return -1;



	return 0;

}



static bool ip_has_options(unsigned int thoff)

{

	return thoff != sizeof(struct iphdr);

}



static int nf_flow_tuple_ip(struct sk_buff *skb, const struct net_device *dev,

			    struct flow_offload_tuple *tuple)

{

	struct flow_ports *ports;

	unsigned int thoff;

	struct iphdr *iph;



	if (!pskb_may_pull(skb, sizeof(*iph)))

		return -1;



	iph = ip_hdr(skb);

	thoff = iph->ihl * 4;



	if (ip_is_fragment(iph) ||

	    unlikely(ip_has_options(thoff)))

		return -1;



	if (iph->protocol != IPPROTO_TCP &&

	    iph->protocol != IPPROTO_UDP)

		return -1;



	thoff = iph->ihl * 4;

	if (!pskb_may_pull(skb, thoff + sizeof(*ports)))

		return -1;



	ports = (struct flow_ports *)(skb_network_header(skb) + thoff);



	tuple->src_v4.s_addr	= iph->saddr;

	tuple->dst_v4.s_addr	= iph->daddr;

	tuple->src_port		= ports->source;

	tuple->dst_port		= ports->dest;

	tuple->l3proto		= AF_INET;

	tuple->l4proto		= iph->protocol;

	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 ((ip_hdr(skb)->frag_off & htons(IP_DF)) == 0)

		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 rtable *rt)

{

	u32 mtu;



	mtu = ip_dst_mtu_maybe_forward(&rt->dst, true);

	if (__nf_flow_exceeds_mtu(skb, mtu))

		return true;



	return false;

}



static unsigned int

nf_flow_offload_ip_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;

	const struct rtable *rt;

	struct iphdr *iph;

	__be32 nexthop;



	if (skb->protocol != htons(ETH_P_IP))

		return NF_ACCEPT;



	if (nf_flow_tuple_ip(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 = (const struct rtable *)flow->tuplehash[dir].tuple.dst_cache;

	if (unlikely(nf_flow_exceeds_mtu(skb, rt)))

		return NF_ACCEPT;



	if (skb_try_make_writable(skb, sizeof(*iph)))

		return NF_DROP;



	if (flow->flags & (FLOW_OFFLOAD_SNAT | FLOW_OFFLOAD_DNAT) &&

	    nf_flow_nat_ip(flow, skb, dir) < 0)

		return NF_DROP;



	flow->timeout = (u32)jiffies + NF_FLOW_TIMEOUT;

	iph = ip_hdr(skb);

	ip_decrease_ttl(iph);



	skb->dev = outdev;

	nexthop = rt_nexthop(rt, flow->tuplehash[!dir].tuple.src_v4.s_addr);

	neigh_xmit(NEIGH_ARP_TABLE, outdev, &nexthop, skb);



	return NF_STOLEN;

}



static struct nf_flowtable_type flowtable_ipv4 = {

	.family		= NFPROTO_IPV4,

	.params		= &nf_flow_offload_rhash_params,

	.gc		= nf_flow_offload_work_gc,

	.hook		= nf_flow_offload_ip_hook,

	.owner		= THIS_MODULE,

};



static int __init nf_flow_ipv4_module_init(void)

{

	nft_register_flowtable_type(&flowtable_ipv4);



	return 0;

}



static void __exit nf_flow_ipv4_module_exit(void)

{

	nft_unregister_flowtable_type(&flowtable_ipv4);

}



module_init(nf_flow_ipv4_module_init);

module_exit(nf_flow_ipv4_module_exit);



MODULE_LICENSE("GPL");

MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");

MODULE_ALIAS_NF_FLOWTABLE(AF_INET);

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