android clat service
This software provides the nat 4->6 translation needed for the "clat" part of
the 464xlat standard. It is needed for better IPv4 application support while
on an IPv6-only mobile network connection using 464xlat's nat64 (such as
T-Mobile's IPv6 trial).
A general diagram of how 464xlat works:
http://dan.drown.org/android/clat/Clat-Plat.png
Depends-on: I2392f8127dcd90d16b0f20ff31bcc5aa096db464
Change-Id: If2bc6916fc66fd4bca7cc241c83cfae839b82e15
Signed-off-by: Daniel Drown <dan-android@drown.org>
diff --git a/checksum.c b/checksum.c
new file mode 100644
index 0000000..14b7113
--- /dev/null
+++ b/checksum.c
@@ -0,0 +1,113 @@
+/*
+ * 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 <netinet/in.h>
+#include <netinet/ip.h>
+#include <netinet/ip_icmp.h>
+#include <netinet/udp.h>
+#include <netinet/tcp.h>
+#include <netinet/ip6.h>
+#include <netinet/icmp6.h>
+#include <linux/icmp.h>
+
+#include "checksum.h"
+
+/* function: ip_checksum_add
+ * adds data to a checksum
+ * current_sum - 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_sum, const void *data, int len) {
+ uint32_t checksum = current_sum;
+ 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_finish
+ * close the checksum
+ * temp_sum - sum from ip_checksum_add
+ */
+uint16_t ip_checksum_finish(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
+ * 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) {
+ 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
+ * current_sum - the current checksum or 0 to start a new checksum
+ * ip6 - the ipv6 header
+ */
+uint32_t ipv6_pseudo_header_checksum(uint32_t current_sum, const struct ip6_hdr *ip6) {
+ uint32_t checksum_len, checksum_next;
+
+ checksum_len = htonl(ntohs(ip6->ip6_plen));
+ checksum_next = htonl(ip6->ip6_nxt);
+
+ current_sum = ip_checksum_add(current_sum,&(ip6->ip6_src),sizeof(struct in6_addr));
+ current_sum = ip_checksum_add(current_sum,&(ip6->ip6_dst),sizeof(struct in6_addr));
+ current_sum = ip_checksum_add(current_sum,&checksum_len,sizeof(checksum_len));
+ current_sum = ip_checksum_add(current_sum,&checksum_next,sizeof(checksum_next));
+
+ return current_sum;
+}
+
+/* function: ipv4_pseudo_header_checksum
+ * calculate the pseudo header checksum for use in tcp/udp headers
+ * current_sum - the current checksum or 0 to start a new checksum
+ * ip - the ipv4 header
+ */
+uint32_t ipv4_pseudo_header_checksum(uint32_t current_sum, const struct iphdr *ip) {
+ uint16_t temp_protocol, temp_length;
+
+ temp_protocol = htons(ip->protocol);
+ temp_length = htons(ntohs(ip->tot_len) - ip->ihl*4);
+
+ current_sum = ip_checksum_add(current_sum, &(ip->saddr), sizeof(uint32_t));
+ current_sum = ip_checksum_add(current_sum, &(ip->daddr), sizeof(uint32_t));
+ current_sum = ip_checksum_add(current_sum, &temp_protocol, sizeof(uint16_t));
+ current_sum = ip_checksum_add(current_sum, &temp_length, sizeof(uint16_t));
+
+ return current_sum;
+}
