Improve checksum calculation and address checking
1. Add a function that calculates the checksum of all the packet
components starting from the specified position. This
simplifies the code a bit and makes it easier to translate
nested packets like ICMP error messages.
2. Don't hardcode IP source and destination addresses. This is
required to translate ICMP error messages.
Bug: 8276725
Change-Id: I2cae45683ae3943e508608fd0a140180dbc60823
diff --git a/translate.c b/translate.c
index c0bd59a..4092bcc 100644
--- a/translate.c
+++ b/translate.c
@@ -33,21 +33,81 @@
#include "logging.h"
#include "debug.h"
-/* function: payload_length
- * calculates the total length of the packet components after pos
+/* function: packet_checksum
+ * calculates the checksum over all the packet components starting from pos
+ * checksum - checksum of packet components before pos
+ * packet - packet to calculate the checksum of
+ * pos - position to start counting from
+ * returns - the completed 16-bit checksum, ready to write into a checksum header field
+ */
+uint16_t packet_checksum(uint32_t checksum, clat_packet packet, int pos) {
+ int i;
+ for (i = pos; i < CLAT_POS_MAX; i++) {
+ if (packet[i].iov_len > 0) {
+ checksum = ip_checksum_add(checksum, packet[i].iov_base, packet[i].iov_len);
+ }
+ }
+ return ip_checksum_finish(checksum);
+}
+
+/* function: packet_length
+ * returns the total length of all the packet components after pos
* packet - packet to calculate the length of
* pos - position to start counting from
* returns: the total length of the packet components after pos
*/
-uint16_t payload_length(clat_packet packet, int pos) {
+uint16_t packet_length(clat_packet packet, int pos) {
size_t len = 0;
int i;
- for (i = pos + 1; i < POS_MAX; i++) {
+ for (i = pos + 1; i < CLAT_POS_MAX; i++) {
len += packet[i].iov_len;
}
return len;
}
+/* function: is_in_plat_subnet
+ * returns true iff the given IPv6 address is in the plat subnet.
+ * addr - IPv6 address
+ */
+int is_in_plat_subnet(const struct in6_addr *addr6) {
+ // Assumes a /96 plat subnet.
+ return (addr6 != NULL) && (memcmp(addr6, &Global_Clatd_Config.plat_subnet, 12) == 0);
+}
+
+/* function: ipv6_addr_to_ipv4_addr
+ * return the corresponding ipv4 address for the given ipv6 address
+ * addr6 - ipv6 address
+ * returns: the IPv4 address
+ */
+uint32_t ipv6_addr_to_ipv4_addr(const struct in6_addr *addr6) {
+
+ if (is_in_plat_subnet(addr6)) {
+ // Assumes a /96 plat subnet.
+ return addr6->s6_addr32[3];
+ } else {
+ // Currently this can only be our own address; other packets are dropped by ipv6_packet.
+ return Global_Clatd_Config.ipv4_local_subnet.s_addr;
+ }
+}
+
+/* function: ipv4_addr_to_ipv6_addr
+ * return the corresponding ipv6 address for the given ipv4 address
+ * addr4 - ipv4 address
+ */
+struct in6_addr ipv4_addr_to_ipv6_addr(uint32_t addr4) {
+ struct in6_addr addr6;
+ // Both addresses are in network byte order (addr4 comes from a network packet, and the config
+ // file entry is read using inet_ntop).
+ if (addr4 == Global_Clatd_Config.ipv4_local_subnet.s_addr) {
+ return Global_Clatd_Config.ipv6_local_subnet;
+ } else {
+ // Assumes a /96 plat subnet.
+ addr6 = Global_Clatd_Config.plat_subnet;
+ addr6.s6_addr32[3] = addr4;
+ return addr6;
+ }
+}
+
/* function: fill_tun_header
* fill in the header for the tun fd
* tun_header - tunnel header, already allocated
@@ -58,16 +118,6 @@
tun_header->proto = htons(proto);
}
-/* function: ipv6_src_to_ipv4_src
- * return the corresponding ipv4 address for the given ipv6 address
- * sourceaddr - ipv6 source address
- * returns: the IPv4 address
- */
-uint32_t ipv6_src_to_ipv4_src(const struct in6_addr *sourceaddr) {
- // assumes a /96 plat subnet
- return sourceaddr->s6_addr32[3];
-}
-
/* function: fill_ip_header
* generate an ipv4 header from an ipv6 header
* ip_targ - (ipv4) target packet header, source: original ipv4 addr, dest: local subnet addr
@@ -89,22 +139,8 @@
ip->protocol = protocol;
ip->check = 0;
- ip->saddr = ipv6_src_to_ipv4_src(&old_header->ip6_src);
- ip->daddr = Global_Clatd_Config.ipv4_local_subnet.s_addr;
-}
-
-/* function: ipv4_dst_to_ipv6_dst
- * return the corresponding ipv6 address for the given ipv4 address
- * destination - ipv4 destination address (network byte order)
- */
-struct in6_addr ipv4_dst_to_ipv6_dst(uint32_t destination) {
- struct in6_addr v6_destination;
-
- // assumes a /96 plat subnet
- v6_destination = Global_Clatd_Config.plat_subnet;
- v6_destination.s6_addr32[3] = destination;
-
- return v6_destination;
+ ip->saddr = ipv6_addr_to_ipv4_addr(&old_header->ip6_src);
+ ip->daddr = ipv6_addr_to_ipv4_addr(&old_header->ip6_dst);
}
/* function: fill_ip6_header
@@ -123,8 +159,8 @@
ip6->ip6_nxt = protocol;
ip6->ip6_hlim = old_header->ttl;
- ip6->ip6_src = Global_Clatd_Config.ipv6_local_subnet;
- ip6->ip6_dst = ipv4_dst_to_ipv6_dst(old_header->daddr);
+ ip6->ip6_src = ipv4_addr_to_ipv6_addr(old_header->saddr);
+ ip6->ip6_dst = ipv4_addr_to_ipv6_addr(old_header->daddr);
}
/* function: icmp_to_icmp6
@@ -152,16 +188,14 @@
icmp6_targ->icmp6_id = icmp->un.echo.id;
icmp6_targ->icmp6_seq = icmp->un.echo.sequence;
- icmp6_targ->icmp6_cksum = 0;
- checksum = ip_checksum_add(checksum, icmp6_targ, sizeof(struct icmp6_hdr));
- checksum = ip_checksum_add(checksum, payload, payload_size);
- icmp6_targ->icmp6_cksum = ip_checksum_finish(checksum);
-
out[pos].iov_len = sizeof(struct icmp6_hdr);
- out[POS_PAYLOAD].iov_base = (char *) payload;
- out[POS_PAYLOAD].iov_len = payload_size;
+ out[CLAT_POS_PAYLOAD].iov_base = (char *) payload;
+ out[CLAT_POS_PAYLOAD].iov_len = payload_size;
- return POS_PAYLOAD + 1;
+ icmp6_targ->icmp6_cksum = 0; // Checksum field must be 0 when calculating checksum.
+ icmp6_targ->icmp6_cksum = packet_checksum(checksum, out, pos);
+
+ return CLAT_POS_PAYLOAD + 1;
}
/* function: icmp6_to_icmp
@@ -189,16 +223,14 @@
icmp_targ->un.echo.id = icmp6->icmp6_id;
icmp_targ->un.echo.sequence = icmp6->icmp6_seq;
- icmp_targ->checksum = 0;
- checksum = ip_checksum_add(0, icmp_targ, sizeof(struct icmphdr));
- checksum = ip_checksum_add(checksum, (void *)payload, payload_size);
- icmp_targ->checksum = ip_checksum_finish(checksum);
-
out[pos].iov_len = sizeof(struct icmphdr);
- out[POS_PAYLOAD].iov_base = (char *) payload;
- out[POS_PAYLOAD].iov_len = payload_size;
+ out[CLAT_POS_PAYLOAD].iov_base = (char *) payload;
+ out[CLAT_POS_PAYLOAD].iov_len = payload_size;
- return POS_PAYLOAD + 1;
+ icmp_targ->checksum = 0; // Checksum field must be 0 when calculating checksum.
+ icmp_targ->checksum = packet_checksum(0, out, pos);
+
+ return CLAT_POS_PAYLOAD + 1;
}
/* function: udp_packet
@@ -271,17 +303,15 @@
struct udphdr *udp_targ = out[pos].iov_base;
memcpy(udp_targ, udp, sizeof(struct udphdr));
- udp_targ->check = 0; // reset checksum, to be calculated
-
- checksum = ip_checksum_add(checksum, udp_targ, sizeof(struct udphdr));
- checksum = ip_checksum_add(checksum, payload, payload_size);
- udp_targ->check = ip_checksum_finish(checksum);
out[pos].iov_len = sizeof(struct udphdr);
- out[POS_PAYLOAD].iov_base = (char *) payload;
- out[POS_PAYLOAD].iov_len = payload_size;
+ out[CLAT_POS_PAYLOAD].iov_base = (char *) payload;
+ out[CLAT_POS_PAYLOAD].iov_len = payload_size;
- return POS_PAYLOAD + 1;
+ udp_targ->check = 0; // Checksum field must be 0 when calculating checksum.
+ udp_targ->check = packet_checksum(checksum, out, pos);
+
+ return CLAT_POS_PAYLOAD + 1;
}
/* function: tcp_translate
@@ -312,13 +342,11 @@
memcpy(tcp_targ, tcp, header_size);
- tcp_targ->check = 0;
- checksum = ip_checksum_add(checksum, tcp_targ, header_size);
- checksum = ip_checksum_add(checksum, payload, payload_size);
- tcp_targ->check = ip_checksum_finish(checksum);
+ out[CLAT_POS_PAYLOAD].iov_base = (char *)payload;
+ out[CLAT_POS_PAYLOAD].iov_len = payload_size;
- out[POS_PAYLOAD].iov_base = (char *)payload;
- out[POS_PAYLOAD].iov_len = payload_size;
+ tcp_targ->check = 0; // Checksum field must be 0 when calculating checksum.
+ tcp_targ->check = packet_checksum(checksum, out, pos);
- return POS_PAYLOAD + 1;
+ return CLAT_POS_PAYLOAD + 1;
}