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>

diff --git a/net/ipv4/netfilter/Kconfig b/net/ipv4/netfilter/Kconfig
index cee5104..7d5d444 100644 (file)
--- a/net/ipv4/netfilter/Kconfig
+++ b/net/ipv4/netfilter/Kconfig
@@ -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

diff --git a/net/ipv4/netfilter/Makefile b/net/ipv4/netfilter/Makefile
index adcdae3..8bb1f0c 100644 (file)
--- a/net/ipv4/netfilter/Makefile
+++ b/net/ipv4/netfilter/Makefile
@@ -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
 

diff --git a/net/ipv4/netfilter/nf_flow_table_ipv4.c b/net/ipv4/netfilter/nf_flow_table_ipv4.c
new file mode 100644 (file)
index 0000000..ac56c0f
--- /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);