Partial checksum updates for TCP and UDP

src/checksum.c

@@ -64,6 +64,49 @@ unsigned short checksum(const void *data, int length)
 	return ~sum;
 }
 
+/**
+ * General checksum update computation function. Inspired by algorithm
+ * in RFC3022.
+ *
+ * @param	old_sum		Old checksum
+ * @param	old_data	Pointer to old part of data. Must be of even
+ * 				number of octets
+ * @param	old_len		Length of old data
+ * @param	new_data	Pointer to new part of data. Must be of even
+ * 				number of octets
+ * @param	new_len		Length of new data
+ *
+ * @return			Updated checksum
+ */
+unsigned short checksum_update(unsigned short old_sum,
+			       unsigned short *old_data, short old_len,
+			       unsigned short *new_data, short new_len)
+{
+	unsigned int sum;
+
+	sum = ~old_sum & 0xffff;
+
+	while (old_len) {
+		sum -= *old_data++;
+		if (sum & 0x80000000) {
+			sum--;
+			sum &= 0xffff;
+		}
+		old_len -= 2;
+	}
+
+	while (new_len) {
+		sum += *new_data++;
+		if (sum & 0x00010000) {
+			sum++;
+			sum &= 0xffff;
+		}
+		new_len -= 2;
+	}
+
+	return ~sum & 0xffff;
+}
+
 /**
  * IPv4 checksum computation function
  *
@@ -147,3 +190,81 @@ unsigned short checksum_ipv6(struct s_ipv6_addr ip_src,
 
 	return sum;
 }
+
+/**
+ * IPv4 checksum update computation function
+ *
+ * @param	old_sum		Old checksum
+ * @param	ip6_src		Original source IPv6 address
+ * @param	ip6_dest	Original destination IPv6 address
+ * @param	old_port	Original transport layer address (port)
+ * @param	ip4_src		New source IPv4 address
+ * @param	ip4_dest	New destination IPv4 address
+ * @param	new_port	New transport layer address (port)
+ *
+ * @return			Checksum
+ */
+unsigned short checksum_ipv4_update(unsigned short old_sum,
+				    struct s_ipv6_addr ip6_src,
+				    struct s_ipv6_addr ip6_dest,
+				    unsigned short old_port,
+				    struct s_ipv4_addr ip4_src,
+				    struct s_ipv4_addr ip4_dest,
+				    unsigned short new_port)
+{
+	struct s_ipv4_pseudo_delta delta4;
+	struct s_ipv6_pseudo_delta delta6;
+
+	delta4.ip_src	= ip4_src;
+	delta4.ip_dest	= ip4_dest;
+	delta4.port	= new_port;
+
+	delta6.ip_src	= ip6_src;
+	delta6.ip_dest	= ip6_dest;
+	delta6.port	= old_port;
+
+	return checksum_update(old_sum,
+			       (unsigned short *) &delta6,
+			       sizeof(struct s_ipv6_pseudo_delta),
+			       (unsigned short *) &delta4,
+			       sizeof(struct s_ipv4_pseudo_delta));
+}
+
+/**
+ * IPv6 checksum update computation function
+ *
+ * @param	old_sum		Old checksum
+ * @param	ip4_src		Original source IPv4 address
+ * @param	ip4_dest	Original destination IPv4 address
+ * @param	old_port	Original transport layer address (port)
+ * @param	ip6_src		New source IPv6 address
+ * @param	ip6_dest	New destination IPv6 address
+ * @param	new_port	New transport layer address (port)
+ *
+ * @return			Checksum
+ */
+unsigned short checksum_ipv6_update(unsigned short old_sum,
+				    struct s_ipv4_addr ip4_src,
+				    struct s_ipv4_addr ip4_dest,
+				    unsigned short old_port,
+				    struct s_ipv6_addr ip6_src,
+				    struct s_ipv6_addr ip6_dest,
+				    unsigned short new_port)
+{
+	struct s_ipv4_pseudo_delta delta4;
+	struct s_ipv6_pseudo_delta delta6;
+
+	delta4.ip_src	= ip4_src;
+	delta4.ip_dest	= ip4_dest;
+	delta4.port	= old_port;
+
+	delta6.ip_src	= ip6_src;
+	delta6.ip_dest	= ip6_dest;
+	delta6.port	= new_port;
+
+	return checksum_update(old_sum,
+			       (unsigned short *) &delta4,
+			       sizeof(struct s_ipv4_pseudo_delta),
+			       (unsigned short *) &delta6,
+			       sizeof(struct s_ipv6_pseudo_delta));
+}

src/checksum.h

@@ -23,11 +23,28 @@
 #include "ipv6.h"
 
 unsigned short checksum(const void *data, int length);
+unsigned short checksum_update(unsigned short old_sum,
+			       unsigned short *old_data, short old_len,
+			       unsigned short *new_data, short new_len);
 unsigned short checksum_ipv4(struct s_ipv4_addr ip_src,
 			     struct s_ipv4_addr ip_dest, unsigned short length,
 			     unsigned char proto, unsigned char *payload);
 unsigned short checksum_ipv6(struct s_ipv6_addr ip_src,
 			     struct s_ipv6_addr ip_dest, unsigned short length,
 			     unsigned char proto, unsigned char *payload);
+unsigned short checksum_ipv4_update(unsigned short old_sum,
+				    struct s_ipv6_addr ip6_src,
+				    struct s_ipv6_addr ip6_dest,
+				    unsigned short old_port,
+				    struct s_ipv4_addr ip4_src,
+				    struct s_ipv4_addr ip4_dest,
+				    unsigned short new_port);
+unsigned short checksum_ipv6_update(unsigned short old_sum,
+				    struct s_ipv4_addr ip4_src,
+				    struct s_ipv4_addr ip4_dest,
+				    unsigned short old_port,
+				    struct s_ipv6_addr ip6_src,
+				    struct s_ipv6_addr ip6_dest,
+				    unsigned short new_port);
 
 #endif /* CHECKSUM_H */

src/ipv4.h

@@ -56,6 +56,13 @@ struct s_ipv4_pseudo {
 	unsigned short		len;		/* 16 b; payload length */
 } __attribute__ ((__packed__));
 
+/* IPv4 pseudoheader structure for checksum update */
+struct s_ipv4_pseudo_delta {
+	struct s_ipv4_addr	ip_src;		/* 32 b; source address */
+	struct s_ipv4_addr	ip_dest;	/* 32 b; destination address */
+	unsigned short		port;		/* 16 b; transport layer address */
+} __attribute__ ((__packed__));
+
 int ipv4(struct s_ethernet *eth, char *packet);
 
 #endif /* IPV4_H */

src/ipv6.h

@@ -47,6 +47,13 @@ struct s_ipv6_pseudo {
 	unsigned char		next_header;	/*   8 b; next header */
 } __attribute__ ((__packed__));
 
+/* IPv6 pseudoheader structure for checksum update */
+struct s_ipv6_pseudo_delta {
+	struct s_ipv6_addr	ip_src;		/* 128 b; source address */
+	struct s_ipv6_addr	ip_dest;	/* 128 b; destination address */
+	unsigned short		port;		/*  16 b; transport layer address */
+} __attribute__ ((__packed__));
+
 int ipv6(struct s_ethernet *eth, char *packet);
 
 #endif /* IPV6_H */

src/tcp.c

@@ -110,9 +110,11 @@ int tcp_ipv4(struct s_ethernet *eth, struct s_ipv4 *ip4, char *payload,
 	tcp->port_dest = connection->ipv6_port_src;
 
 	/* compute TCP checksum */
-	tcp->checksum = 0x0;
+	tcp->checksum = checksum_ipv6_update(tcp->checksum,
-	tcp->checksum = checksum_ipv6(ip6->ip_src, ip6->ip_dest, payload_size,
+					     ip4->ip_src, ip4->ip_dest,
-				      IPPROTO_TCP, (unsigned char *) tcp);
+					     connection->ipv4_port_src,
+					     ip6->ip_src, ip6->ip_dest,
+					     connection->ipv6_port_src);
 
 	/* copy the payload data (with new checksum) */
 	memcpy(packet + sizeof(struct s_ethernet) + sizeof(struct s_ipv6),
@@ -198,10 +200,11 @@ int tcp_ipv6(struct s_ethernet *eth, struct s_ipv6 *ip6, char *payload)
 	tcp->port_src = connection->ipv4_port_src;
 
 	/* compute TCP checksum */
-	tcp->checksum = 0;
+	tcp->checksum = checksum_ipv4_update(tcp->checksum,
-	tcp->checksum = checksum_ipv4(ip4->ip_src, ip4->ip_dest,
+					     ip6->ip_src, ip6->ip_dest,
-				      htons(ip6->len), IPPROTO_TCP,
+					     connection->ipv6_port_src,
-				      (unsigned char *) tcp);
+					     ip4->ip_src, ip4->ip_dest,
+					     connection->ipv4_port_src);
 
 	/* copy the payload data (with new checksum) */
 	memcpy(packet + sizeof(struct s_ipv4), payload, htons(ip6->len));

src/udp.c

@@ -110,9 +110,17 @@ int udp_ipv4(struct s_ethernet *eth, struct s_ipv4 *ip4, char *payload,
 	udp->port_dest = connection->ipv6_port_src;
 
 	/* compute UDP checksum */
-	udp->checksum = 0x0;
+	if (udp->checksum) {
-	udp->checksum = checksum_ipv6(ip6->ip_src, ip6->ip_dest, payload_size,
+		udp->checksum = checksum_ipv6_update(udp->checksum,
-				      IPPROTO_UDP, (unsigned char *) udp);
+						     ip4->ip_src, ip4->ip_dest,
+						     connection->ipv4_port_src,
+						     ip6->ip_src, ip6->ip_dest,
+						     connection->ipv6_port_src);
+	} else {
+		/* if original checksum was 0x0000, we need to compute it */
+		udp->checksum = checksum_ipv6(ip6->ip_src, ip6->ip_dest, payload_size,
+					      IPPROTO_UDP, (unsigned char *) udp);
+	}
 
 	/* copy the payload data (with new checksum) */
 	memcpy(packet + sizeof(struct s_ethernet) + sizeof(struct s_ipv6),
@@ -198,10 +206,11 @@ int udp_ipv6(struct s_ethernet *eth, struct s_ipv6 *ip6, char *payload)
 	udp->port_src = connection->ipv4_port_src;
 
 	/* compute UDP checksum */
-	udp->checksum = 0x0;
+	udp->checksum = checksum_ipv4_update(udp->checksum,
-	udp->checksum = checksum_ipv4(ip4->ip_src, ip4->ip_dest,
+					     ip6->ip_src, ip6->ip_dest,
-				      htons(ip6->len), IPPROTO_UDP,
+					     connection->ipv6_port_src,
-				      (unsigned char *) payload);
+					     ip4->ip_src, ip4->ip_dest,
+					     connection->ipv4_port_src);
 
 	/* copy the payload data (with new checksum) */
 	memcpy(packet + sizeof(struct s_ipv4), payload, htons(ip6->len));