#define MAXPACKETSIZE (65536 - 60 - 8) /* TODO: What are the magic numbers? */
#define DEFAULTDATALEN (64 - 8) /* TODO: What are the magic numbers? */
+/* ICMP header contains: type, code, checksum, identifier and sequence number. */
+#define ICMP_ECHO_HEADER_BYTES 8
+#define ICMP_ECHO_DATA_BYTES sizeof(struct timeval)
+#define ICMP_ECHO_PACKET_BYTES ICMP_ECHO_HEADER_BYTES + ICMP_ECHO_DATA_BYTES
+
/* Must be larger than the length of the longest configuration key (currently 'start_condition'). */
#define MAXCONFKEYLEN 20
static bool retry_down_cmd = false;
/*
- * Checksum routine for Internet Protocol family headers
+ * Generate an Internet Checksum per RFC 1071.
+ *
+ * This is not a general purpose implementation of RFC 1071. Since we only
+ * send ICMP echo packets, we assume 'data' will contain a specific number of
+ * bytes.
*/
-static int
-in_cksum(unsigned short * addr, int len)
+uint16_t
+checksum(uint16_t * data)
{
- int nleft = len;
- unsigned short * w = addr;
- int sum = 0;
- unsigned short answer = 0;
-
- /*
- * Our algorithm is simple, using a 32 bit accumulator (sum), we add
- * sequential 16 bit words to it, and at the end, fold back all the
- * carry bits from the top 16 bits into the lower 16 bits.
- */
- while (nleft > 1) {
- sum += *w++;
- nleft -= 2;
+ uint32_t accumulator = 0;
+ for (size_t i = 0; i < ICMP_ECHO_PACKET_BYTES / 2; i++) {
+ accumulator += ntohs(data[i]);
+ if (accumulator > 0xffff) accumulator -= 0xffff;
}
-
- /* mop up an odd byte, if necessary */
- if (nleft == 1) {
- *(u_char *)(&answer) = *(u_char *)w;
- sum += answer;
- }
-
- /* add back carry outs from top 16 bits to low 16 bits */
- sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */
- sum += (sum >> 16); /* add carry */
- answer = ~sum; /* truncate to 16 bits */
- return(answer);
+ return htons(~accumulator);
}
/*
int i;
struct icmp * icp;
struct monitor_host * p = hosts;
- u_char outpack[MAXPACKETSIZE];
+ unsigned char outpack[MAXPACKETSIZE]; /* Use char so this can be aliased later. */
while (p) {
if (p->socket != -1) {
int cc = DEFAULTDATALEN + 8; /* skips ICMP portion */
- /* compute ICMP checksum */
- icp->icmp_cksum = in_cksum((unsigned short *) icp, cc);
+ icp->icmp_cksum = checksum((uint16_t *) outpack);
i = sendto(p->socket, (char *) outpack, cc, 0, (const struct sockaddr *) (&p->dest), sizeof(struct sockaddr));