netfilter: flowtable: split IPv4 datapath in helper functions

Add context structure and helper functions to look up for a matching
IPv4 entry in the flowtable and to forward packets.

No functional changes are intended.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Florian Westphal <fw@strlen.de>

net/netfilter/nf_flow_table_ip.c

@@ -163,38 +163,43 @@ static void nf_flow_tuple_encap(struct sk_buff *skb,
 	}
 }
 
-static int nf_flow_tuple_ip(struct sk_buff *skb, const struct net_device *dev,
-			    struct flow_offload_tuple *tuple, u32 *hdrsize,
-			    u32 offset)
+struct nf_flowtable_ctx {
+	const struct net_device	*in;
+	u32			offset;
+	u32			hdrsize;
+};
+
+static int nf_flow_tuple_ip(struct nf_flowtable_ctx *ctx, struct sk_buff *skb,
+			    struct flow_offload_tuple *tuple)
 {
 	struct flow_ports *ports;
 	unsigned int thoff;
 	struct iphdr *iph;
 	u8 ipproto;
 
-	if (!pskb_may_pull(skb, sizeof(*iph) + offset))
+	if (!pskb_may_pull(skb, sizeof(*iph) + ctx->offset))
 		return -1;
 
-	iph = (struct iphdr *)(skb_network_header(skb) + offset);
+	iph = (struct iphdr *)(skb_network_header(skb) + ctx->offset);
 	thoff = (iph->ihl * 4);
 
 	if (ip_is_fragment(iph) ||
 	    unlikely(ip_has_options(thoff)))
 		return -1;
 
-	thoff += offset;
+	thoff += ctx->offset;
 
 	ipproto = iph->protocol;
 	switch (ipproto) {
 	case IPPROTO_TCP:
-		*hdrsize = sizeof(struct tcphdr);
+		ctx->hdrsize = sizeof(struct tcphdr);
 		break;
 	case IPPROTO_UDP:
-		*hdrsize = sizeof(struct udphdr);
+		ctx->hdrsize = sizeof(struct udphdr);
 		break;
 #ifdef CONFIG_NF_CT_PROTO_GRE
 	case IPPROTO_GRE:
-		*hdrsize = sizeof(struct gre_base_hdr);
+		ctx->hdrsize = sizeof(struct gre_base_hdr);
 		break;
 #endif
 	default:
@@ -204,7 +209,7 @@ static int nf_flow_tuple_ip(struct sk_buff *skb, const struct net_device *dev,
 	if (iph->ttl <= 1)
 		return -1;
 
-	if (!pskb_may_pull(skb, thoff + *hdrsize))
+	if (!pskb_may_pull(skb, thoff + ctx->hdrsize))
 		return -1;
 
 	switch (ipproto) {
@@ -224,13 +229,13 @@ static int nf_flow_tuple_ip(struct sk_buff *skb, const struct net_device *dev,
 	}
 	}
 
-	iph = (struct iphdr *)(skb_network_header(skb) + offset);
+	iph = (struct iphdr *)(skb_network_header(skb) + ctx->offset);
 
 	tuple->src_v4.s_addr	= iph->saddr;
 	tuple->dst_v4.s_addr	= iph->daddr;
 	tuple->l3proto		= AF_INET;
 	tuple->l4proto		= ipproto;
-	tuple->iifidx		= dev->ifindex;
+	tuple->iifidx		= ctx->in->ifindex;
 	nf_flow_tuple_encap(skb, tuple);
 
 	return 0;
@@ -336,58 +341,56 @@ static unsigned int nf_flow_queue_xmit(struct net *net, struct sk_buff *skb,
 	return NF_STOLEN;
 }
 
-unsigned int
-nf_flow_offload_ip_hook(void *priv, struct sk_buff *skb,
-			const struct nf_hook_state *state)
+static struct flow_offload_tuple_rhash *
+nf_flow_offload_lookup(struct nf_flowtable_ctx *ctx,
+		       struct nf_flowtable *flow_table, struct sk_buff *skb)
 {
-	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;
-	u32 hdrsize, offset = 0;
-	unsigned int thoff, mtu;
-	struct rtable *rt;
-	struct iphdr *iph;
-	__be32 nexthop;
-	int ret;
 
 	if (skb->protocol != htons(ETH_P_IP) &&
-	    !nf_flow_skb_encap_protocol(skb, htons(ETH_P_IP), &offset))
-		return NF_ACCEPT;
+	    !nf_flow_skb_encap_protocol(skb, htons(ETH_P_IP), &ctx->offset))
+		return NULL;
 
-	if (nf_flow_tuple_ip(skb, state->in, &tuple, &hdrsize, offset) < 0)
-		return NF_ACCEPT;
+	if (nf_flow_tuple_ip(ctx, skb, &tuple) < 0)
+		return NULL;
 
-	tuplehash = flow_offload_lookup(flow_table, &tuple);
-	if (tuplehash == NULL)
-		return NF_ACCEPT;
+	return flow_offload_lookup(flow_table, &tuple);
+}
+
+static int nf_flow_offload_forward(struct nf_flowtable_ctx *ctx,
+				   struct nf_flowtable *flow_table,
+				   struct flow_offload_tuple_rhash *tuplehash,
+				   struct sk_buff *skb)
+{
+	enum flow_offload_tuple_dir dir;
+	struct flow_offload *flow;
+	unsigned int thoff, mtu;
+	struct iphdr *iph;
 
 	dir = tuplehash->tuple.dir;
 	flow = container_of(tuplehash, struct flow_offload, tuplehash[dir]);
 
-	mtu = flow->tuplehash[dir].tuple.mtu + offset;
+	mtu = flow->tuplehash[dir].tuple.mtu + ctx->offset;
 	if (unlikely(nf_flow_exceeds_mtu(skb, mtu)))
-		return NF_ACCEPT;
+		return 0;
 
-	iph = (struct iphdr *)(skb_network_header(skb) + offset);
-	thoff = (iph->ihl * 4) + offset;
+	iph = (struct iphdr *)(skb_network_header(skb) + ctx->offset);
+	thoff = (iph->ihl * 4) + ctx->offset;
 	if (nf_flow_state_check(flow, iph->protocol, skb, thoff))
-		return NF_ACCEPT;
+		return 0;
 
 	if (!nf_flow_dst_check(&tuplehash->tuple)) {
 		flow_offload_teardown(flow);
-		return NF_ACCEPT;
+		return 0;
 	}
 
-	if (skb_try_make_writable(skb, thoff + hdrsize))
-		return NF_DROP;
+	if (skb_try_make_writable(skb, thoff + ctx->hdrsize))
+		return -1;
 
 	flow_offload_refresh(flow_table, flow);
 
 	nf_flow_encap_pop(skb, tuplehash);
-	thoff -= offset;
+	thoff -= ctx->offset;
 
 	iph = ip_hdr(skb);
 	nf_flow_nat_ip(flow, skb, thoff, dir, iph);
@@ -398,6 +401,35 @@ nf_flow_offload_ip_hook(void *priv, struct sk_buff *skb,
 	if (flow_table->flags & NF_FLOWTABLE_COUNTER)
 		nf_ct_acct_update(flow->ct, tuplehash->tuple.dir, skb->len);
 
+	return 1;
+}
+
+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;
+	enum flow_offload_tuple_dir dir;
+	struct nf_flowtable_ctx ctx = {
+		.in	= state->in,
+	};
+	struct flow_offload *flow;
+	struct net_device *outdev;
+	struct rtable *rt;
+	__be32 nexthop;
+	int ret;
+
+	tuplehash = nf_flow_offload_lookup(&ctx, flow_table, skb);
+	if (!tuplehash)
+		return NF_ACCEPT;
+
+	ret = nf_flow_offload_forward(&ctx, flow_table, tuplehash, skb);
+	if (ret < 0)
+		return NF_DROP;
+	else if (ret == 0)
+		return NF_ACCEPT;
+
 	if (unlikely(tuplehash->tuple.xmit_type == FLOW_OFFLOAD_XMIT_XFRM)) {
 		rt = (struct rtable *)tuplehash->tuple.dst_cache;
 		memset(skb->cb, 0, sizeof(struct inet_skb_parm));
@@ -406,6 +438,9 @@ nf_flow_offload_ip_hook(void *priv, struct sk_buff *skb,
 		return nf_flow_xmit_xfrm(skb, state, &rt->dst);
 	}
 
+	dir = tuplehash->tuple.dir;
+	flow = container_of(tuplehash, struct flow_offload, tuplehash[dir]);
+
 	switch (tuplehash->tuple.xmit_type) {
 	case FLOW_OFFLOAD_XMIT_NEIGH:
 		rt = (struct rtable *)tuplehash->tuple.dst_cache;