OpenWrt – Rev 4
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From: Pablo Neira Ayuso <pablo@netfilter.org>
Date: Sun, 7 Jan 2018 01:04:15 +0100
Subject: [PATCH] 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: Pablo Neira Ayuso <pablo@netfilter.org>
---
create mode 100644 net/ipv4/netfilter/nf_flow_table_ipv4.c
--- a/net/ipv4/netfilter/Kconfig
+++ b/net/ipv4/netfilter/Kconfig
@@ -77,6 +77,14 @@ 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
--- a/net/ipv4/netfilter/Makefile
+++ b/net/ipv4/netfilter/Makefile
@@ -43,6 +43,9 @@ obj-$(CONFIG_NFT_REDIR_IPV4) += nft_redi
obj-$(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
--- /dev/null
+++ b/net/ipv4/netfilter/nf_flow_table_ipv4.c
@@ -0,0 +1,283 @@
+#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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