diff --git a/libnetutils/Android.bp b/libnetutils/Android.bp index 1d43775d6..268496f7c 100644 --- a/libnetutils/Android.bp +++ b/libnetutils/Android.bp @@ -6,6 +6,7 @@ cc_library_shared { }, srcs: [ + "checksum.c", "dhcpclient.c", "dhcpmsg.c", "ifc_utils.c", diff --git a/libnetutils/checksum.c b/libnetutils/checksum.c new file mode 100644 index 000000000..74b5fddf6 --- /dev/null +++ b/libnetutils/checksum.c @@ -0,0 +1,145 @@ +/* + * Copyright 2011 Daniel Drown + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + * + * checksum.c - ipv4/ipv6 checksum calculation + */ +#include +#include +#include +#include +#include +#include +#include + +#include "netutils/checksum.h" + +/* function: ip_checksum_add + * adds data to a checksum. only known to work on little-endian hosts + * current - the current checksum (or 0 to start a new checksum) + * data - the data to add to the checksum + * len - length of data + */ +uint32_t ip_checksum_add(uint32_t current, const void* data, int len) { + uint32_t checksum = current; + int left = len; + const uint16_t* data_16 = data; + + while (left > 1) { + checksum += *data_16; + data_16++; + left -= 2; + } + if (left) { + checksum += *(uint8_t*)data_16; + } + + return 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_fold(uint32_t temp_sum) { + while (temp_sum > 0xffff) { + temp_sum = (temp_sum >> 16) + (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 + * len - length of data + */ +uint16_t ip_checksum(const void* data, int len) { + // TODO: consider starting from 0xffff so the checksum of a buffer entirely consisting of zeros + // is correctly calculated as 0. + uint32_t temp_sum; + + temp_sum = ip_checksum_add(0, data, len); + return ip_checksum_finish(temp_sum); +} + +/* function: ipv6_pseudo_header_checksum + * calculate the pseudo header checksum for use in tcp/udp/icmp headers + * 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(const struct ip6_hdr* ip6, uint32_t len, uint8_t protocol) { + uint32_t checksum_len = htonl(len); + uint32_t 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)); + current = ip_checksum_add(current, &checksum_next, sizeof(checksum_next)); + + return current; +} + +/* function: ipv4_pseudo_header_checksum + * calculate the pseudo header checksum for use in tcp/udp headers + * ip - the ipv4 header + * len - the transport length (transport header + payload) + */ +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)); + current = ip_checksum_add(current, &temp_length, sizeof(uint16_t)); + + 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 + } +} diff --git a/libnetutils/include/netutils/checksum.h b/libnetutils/include/netutils/checksum.h new file mode 100644 index 000000000..868217c5d --- /dev/null +++ b/libnetutils/include/netutils/checksum.h @@ -0,0 +1,34 @@ +/* + * Copyright 2011 Daniel Drown + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + * + * checksum.h - checksum functions + */ +#ifndef __CHECKSUM_H__ +#define __CHECKSUM_H__ + +#include +#include +#include + +uint32_t ip_checksum_add(uint32_t current, const void* data, int len); +uint16_t ip_checksum_finish(uint32_t temp_sum); +uint16_t ip_checksum(const void* data, int len); + +uint32_t ipv6_pseudo_header_checksum(const struct ip6_hdr* ip6, uint32_t len, uint8_t protocol); +uint32_t ipv4_pseudo_header_checksum(const struct iphdr* ip, uint16_t len); + +uint16_t ip_checksum_adjust(uint16_t checksum, uint32_t old_hdr_sum, uint32_t new_hdr_sum); + +#endif /* __CHECKSUM_H__ */