netfilter: conntrack: Only need first 4 bytes to get l4proto ports

We only need first 4 bytes instead of 8 bytes to get the ports of
tcp/udp/dccp/sctp/udplite in their pkt_to_tuple function.
Signed-off-by: Gao Feng <fgao@ikuai8.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_proto_dccp.c

@@ -402,7 +402,8 @@ static bool dccp_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
 {
 	struct dccp_hdr _hdr, *dh;
 
-	dh = skb_header_pointer(skb, dataoff, sizeof(_hdr), &_hdr);
+	/* Actually only need first 4 bytes to get ports. */
+	dh = skb_header_pointer(skb, dataoff, 4, &_hdr);
 	if (dh == NULL)
 		return false;
 

net/netfilter/nf_conntrack_proto_sctp.c

@@ -161,8 +161,8 @@ static bool sctp_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
 	const struct sctphdr *hp;
 	struct sctphdr _hdr;
 
-	/* Actually only need first 8 bytes. */
-	hp = skb_header_pointer(skb, dataoff, 8, &_hdr);
+	/* Actually only need first 4 bytes to get ports. */
+	hp = skb_header_pointer(skb, dataoff, 4, &_hdr);
 	if (hp == NULL)
 		return false;
 

net/netfilter/nf_conntrack_proto_tcp.c

@@ -282,8 +282,8 @@ static bool tcp_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
 	const struct tcphdr *hp;
 	struct tcphdr _hdr;
 
-	/* Actually only need first 8 bytes. */
-	hp = skb_header_pointer(skb, dataoff, 8, &_hdr);
+	/* Actually only need first 4 bytes to get ports. */
+	hp = skb_header_pointer(skb, dataoff, 4, &_hdr);
 	if (hp == NULL)
 		return false;
 

net/netfilter/nf_conntrack_proto_udp.c

@@ -44,8 +44,8 @@ static bool udp_pkt_to_tuple(const struct sk_buff *skb,
 	const struct udphdr *hp;
 	struct udphdr _hdr;
 
-	/* Actually only need first 8 bytes. */
-	hp = skb_header_pointer(skb, dataoff, sizeof(_hdr), &_hdr);
+	/* Actually only need first 4 bytes to get ports. */
+	hp = skb_header_pointer(skb, dataoff, 4, &_hdr);
 	if (hp == NULL)
 		return false;
 

net/netfilter/nf_conntrack_proto_udplite.c

@@ -54,7 +54,8 @@ static bool udplite_pkt_to_tuple(const struct sk_buff *skb,
 	const struct udphdr *hp;
 	struct udphdr _hdr;
 
-	hp = skb_header_pointer(skb, dataoff, sizeof(_hdr), &_hdr);
+	/* Actually only need first 4 bytes to get ports. */
+	hp = skb_header_pointer(skb, dataoff, 4, &_hdr);
 	if (hp == NULL)
 		return false;