diff options
Diffstat (limited to 'checksum.c')
| -rw-r--r-- | checksum.c | 54 |
1 files changed, 41 insertions, 13 deletions
@@ -49,19 +49,27 @@ uint32_t ip_checksum_add(uint32_t current, const void *data, int len) { return checksum; } -/* function: ip_checksum_finish - * close the checksum +/* function: ip_checksum_fold + * folds a 32-bit partial checksum into 16 bits * temp_sum - sum from ip_checksum_add + * returns: the folded checksum in network byte order */ -uint16_t ip_checksum_finish(uint32_t temp_sum) { +uint16_t ip_checksum_fold(uint32_t temp_sum) { while(temp_sum > 0xffff) temp_sum = (temp_sum >> 16) + (temp_sum & 0xFFFF); - temp_sum = (~temp_sum) & 0xffff; - return temp_sum; } +/* function: ip_checksum_finish + * folds and closes the checksum + * temp_sum - sum from ip_checksum_add + * returns: a header checksum value in network byte order + */ +uint16_t ip_checksum_finish(uint32_t temp_sum) { + return ~ip_checksum_fold(temp_sum); +} + /* function: ip_checksum * combined ip_checksum_add and ip_checksum_finish * data - data to checksum @@ -76,16 +84,16 @@ uint16_t ip_checksum(const void *data, int len) { /* function: ipv6_pseudo_header_checksum * calculate the pseudo header checksum for use in tcp/udp/icmp headers - * current - the current checksum or 0 to start a new checksum - * ip6 - the ipv6 header - * len - the transport length (transport header + payload) + * ip6 - the ipv6 header + * len - the transport length (transport header + payload) + * protocol - the transport layer protocol, can be different from ip6->ip6_nxt for fragments */ -uint32_t ipv6_pseudo_header_checksum(uint32_t current, const struct ip6_hdr *ip6, uint16_t len) { +uint32_t ipv6_pseudo_header_checksum(const struct ip6_hdr *ip6, uint16_t len, uint8_t protocol) { uint32_t checksum_len, checksum_next; - checksum_len = htonl((uint32_t) len); - checksum_next = htonl(ip6->ip6_nxt); + checksum_next = htonl(protocol); + uint32_t current = 0; current = ip_checksum_add(current, &(ip6->ip6_src), sizeof(struct in6_addr)); current = ip_checksum_add(current, &(ip6->ip6_dst), sizeof(struct in6_addr)); current = ip_checksum_add(current, &checksum_len, sizeof(checksum_len)); @@ -96,16 +104,16 @@ uint32_t ipv6_pseudo_header_checksum(uint32_t current, const struct ip6_hdr *ip6 /* function: ipv4_pseudo_header_checksum * calculate the pseudo header checksum for use in tcp/udp headers - * current - the current checksum or 0 to start a new checksum * ip - the ipv4 header * len - the transport length (transport header + payload) */ -uint32_t ipv4_pseudo_header_checksum(uint32_t current, const struct iphdr *ip, uint16_t len) { +uint32_t ipv4_pseudo_header_checksum(const struct iphdr *ip, uint16_t len) { uint16_t temp_protocol, temp_length; temp_protocol = htons(ip->protocol); temp_length = htons(len); + uint32_t current = 0; current = ip_checksum_add(current, &(ip->saddr), sizeof(uint32_t)); current = ip_checksum_add(current, &(ip->daddr), sizeof(uint32_t)); current = ip_checksum_add(current, &temp_protocol, sizeof(uint16_t)); @@ -113,3 +121,23 @@ uint32_t ipv4_pseudo_header_checksum(uint32_t current, const struct iphdr *ip, u return current; } + +/* function: ip_checksum_adjust + * calculates a new checksum given a previous checksum and the old and new pseudo-header checksums + * checksum - the header checksum in the original packet in network byte order + * old_hdr_sum - the pseudo-header checksum of the original packet + * new_hdr_sum - the pseudo-header checksum of the translated packet + * returns: the new header checksum in network byte order + */ +uint16_t ip_checksum_adjust(uint16_t checksum, uint32_t old_hdr_sum, uint32_t new_hdr_sum) { + // Algorithm suggested in RFC 1624. + // http://tools.ietf.org/html/rfc1624#section-3 + checksum = ~checksum; + uint16_t folded_sum = ip_checksum_fold(checksum + new_hdr_sum); + uint16_t folded_old = ip_checksum_fold(old_hdr_sum); + if (folded_sum > folded_old) { + return ~(folded_sum - folded_old); + } else { + return ~(folded_sum - folded_old - 1); // end-around borrow + } +} |