net/sctp: Refactor SCTP skb checksum computation

This patch consolidates the SCTP checksum calculation code from various
places to a single new function, sctp_compute_cksum(skb, offset).
Signed-off-by: Joe Stringer <joe@wand.net.nz>
Reviewed-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sctp/checksum.h

@@ -85,4 +85,19 @@ static inline __le32 sctp_end_cksum(__u32 crc32)
 	return cpu_to_le32(~crc32);
 }
 
+/* Calculate the CRC32C checksum of an SCTP packet.  */
+static inline __le32 sctp_compute_cksum(const struct sk_buff *skb,
+					unsigned int offset)
+{
+	const struct sk_buff *iter;
+
+	__u32 crc32 = sctp_start_cksum(skb->data + offset,
+				       skb_headlen(skb) - offset);
+	skb_walk_frags(skb, iter)
+		crc32 = sctp_update_cksum((__u8 *) iter->data,
+					  skb_headlen(iter), crc32);
+
+	return sctp_end_cksum(crc32);
+}
+
 #endif /* __sctp_checksum_h__ */

net/netfilter/ipvs/ip_vs_proto_sctp.c

@@ -66,15 +66,7 @@ sctp_conn_schedule(int af, struct sk_buff *skb, struct ip_vs_proto_data *pd,
 static void sctp_nat_csum(struct sk_buff *skb, sctp_sctphdr_t *sctph,
 			  unsigned int sctphoff)
 {
-	__u32 crc32;
-	struct sk_buff *iter;
-
-	crc32 = sctp_start_cksum((__u8 *)sctph, skb_headlen(skb) - sctphoff);
-	skb_walk_frags(skb, iter)
-		crc32 = sctp_update_cksum((u8 *) iter->data,
-					  skb_headlen(iter), crc32);
-	sctph->checksum = sctp_end_cksum(crc32);
-
+	sctph->checksum = sctp_compute_cksum(skb, sctphoff);
 	skb->ip_summed = CHECKSUM_UNNECESSARY;
 }
 
@@ -151,10 +143,7 @@ sctp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp)
 {
 	unsigned int sctphoff;
 	struct sctphdr *sh, _sctph;
-	struct sk_buff *iter;
-	__le32 cmp;
-	__le32 val;
-	__u32 tmp;
+	__le32 cmp, val;
 
 #ifdef CONFIG_IP_VS_IPV6
 	if (af == AF_INET6)
@@ -168,13 +157,7 @@ sctp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp)
 		return 0;
 
 	cmp = sh->checksum;
-
-	tmp = sctp_start_cksum((__u8 *) sh, skb_headlen(skb));
-	skb_walk_frags(skb, iter)
-		tmp = sctp_update_cksum((__u8 *) iter->data,
-					skb_headlen(iter), tmp);
-
-	val = sctp_end_cksum(tmp);
+	val = sctp_compute_cksum(skb, sctphoff);
 
 	if (val != cmp) {
 		/* CRC failure, dump it. */

net/netfilter/nf_nat_proto_sctp.c

@@ -34,9 +34,7 @@ sctp_manip_pkt(struct sk_buff *skb,
 	       const struct nf_conntrack_tuple *tuple,
 	       enum nf_nat_manip_type maniptype)
 {
-	struct sk_buff *frag;
 	sctp_sctphdr_t *hdr;
-	__u32 crc32;
 
 	if (!skb_make_writable(skb, hdroff + sizeof(*hdr)))
 		return false;
@@ -51,11 +49,7 @@ sctp_manip_pkt(struct sk_buff *skb,
 		hdr->dest = tuple->dst.u.sctp.port;
 	}
 
-	crc32 = sctp_start_cksum((u8 *)hdr, skb_headlen(skb) - hdroff);
-	skb_walk_frags(skb, frag)
-		crc32 = sctp_update_cksum((u8 *)frag->data, skb_headlen(frag),
-					  crc32);
-	hdr->checksum = sctp_end_cksum(crc32);
+	hdr->checksum = sctp_compute_cksum(skb, hdroff);
 
 	return true;
 }

net/sctp/input.c

@@ -87,15 +87,7 @@ static inline int sctp_rcv_checksum(struct net *net, struct sk_buff *skb)
 {
 	struct sctphdr *sh = sctp_hdr(skb);
 	__le32 cmp = sh->checksum;
-	struct sk_buff *list;
-	__le32 val;
-	__u32 tmp = sctp_start_cksum((__u8 *)sh, skb_headlen(skb));
-
-	skb_walk_frags(skb, list)
-		tmp = sctp_update_cksum((__u8 *)list->data, skb_headlen(list),
-					tmp);
-
-	val = sctp_end_cksum(tmp);
+	__le32 val = sctp_compute_cksum(skb, 0);
 
 	if (val != cmp) {
 		/* CRC failure, dump it. */