udp: Add udp6_lib_lookup_skb and udp4_lib_lookup_skb

Add externally visible functions to lookup a UDP socket by skb. This
will be used for GRO in UDP sockets. These functions also check
if skb->dst is set, and if it is not skb->dev is used to get dev_net.
This allows calling lookup functions before dst has been set on the
skbuff.
Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/udp.h

@@ -269,6 +269,8 @@ struct sock *udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
 struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
 			       __be32 daddr, __be16 dport, int dif,
 			       struct udp_table *tbl, struct sk_buff *skb);
+struct sock *udp4_lib_lookup_skb(struct sk_buff *skb,
+				 __be16 sport, __be16 dport);
 struct sock *udp6_lib_lookup(struct net *net,
 			     const struct in6_addr *saddr, __be16 sport,
 			     const struct in6_addr *daddr, __be16 dport,
@@ -278,6 +280,8 @@ struct sock *__udp6_lib_lookup(struct net *net,
 			       const struct in6_addr *daddr, __be16 dport,
 			       int dif, struct udp_table *tbl,
 			       struct sk_buff *skb);
+struct sock *udp6_lib_lookup_skb(struct sk_buff *skb,
+				 __be16 sport, __be16 dport);
 
 /*
  * 	SNMP statistics for UDP and UDP-Lite

net/ipv4/udp.c

@@ -604,6 +604,19 @@ static inline struct sock *__udp4_lib_lookup_skb(struct sk_buff *skb,
 				 udptable, skb);
 }
 
+struct sock *udp4_lib_lookup_skb(struct sk_buff *skb,
+				 __be16 sport, __be16 dport)
+{
+	const struct iphdr *iph = ip_hdr(skb);
+	const struct net_device *dev =
+	    skb_dst(skb) ? skb_dst(skb)->dev : skb->dev;
+
+	return __udp4_lib_lookup(dev_net(dev), iph->saddr, sport,
+				 iph->daddr, dport, inet_iif(skb),
+				 &udp_table, skb);
+}
+EXPORT_SYMBOL_GPL(udp4_lib_lookup_skb);
+
 /* Must be called under rcu_read_lock().
  * Does increment socket refcount.
  */

net/ipv6/udp.c

@@ -326,6 +326,19 @@ static struct sock *__udp6_lib_lookup_skb(struct sk_buff *skb,
 				 udptable, skb);
 }
 
+struct sock *udp6_lib_lookup_skb(struct sk_buff *skb,
+				 __be16 sport, __be16 dport)
+{
+	const struct ipv6hdr *iph = ipv6_hdr(skb);
+	const struct net_device *dev =
+	    skb_dst(skb) ? skb_dst(skb)->dev : skb->dev;
+
+	return __udp6_lib_lookup(dev_net(dev), &iph->saddr, sport,
+				 &iph->daddr, dport, inet6_iif(skb),
+				 &udp_table, skb);
+}
+EXPORT_SYMBOL_GPL(udp6_lib_lookup_skb);
+
 /* Must be called under rcu_read_lock().
  * Does increment socket refcount.
  */