X-Git-Url: http://git.subgeniuskitty.com/icmpmonitor/.git/blobdiff_plain/4a0d85a5f1ed0900bf617f86ee238b3c644fe7b8..22e9f47e32f5905d2bd9ae5ee35020ace9091428:/icmpmonitor.c diff --git a/icmpmonitor.c b/icmpmonitor.c index 284da67..462c920 100644 --- a/icmpmonitor.c +++ b/icmpmonitor.c @@ -11,6 +11,12 @@ * See LICENSE file for copyright and license details. */ +/* Wishlist */ +/* TODO: Add IPv6 support. */ +/* TODO: Turn the global '-r' functionality into per-host config file option. */ +/* TODO: Add 'auto' keyword to 'start_condition', testing host on startup. */ +/* TODO: Double-check the network code when interrupted while receiving a packet. */ + #include #include #include @@ -27,6 +33,7 @@ #include #include #include +#include #include "iniparser/iniparser.h" @@ -35,11 +42,20 @@ #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 + +/* Minimum time in seconds between pings. If this value is increased above the */ +/* `ping_interval` for a given host, some pings to that host may not be sent. */ +#define TIMER_RESOLUTION 1 + /* Must be larger than the length of the longest configuration key (currently 'start_condition'). */ #define MAXCONFKEYLEN 20 /* One struct per host as listed in the config file. */ -struct monitor_host { +struct host_entry { /* From the config file */ char * name; int ping_interval; @@ -55,226 +71,187 @@ struct monitor_host { struct sockaddr_in dest; /* Linked list */ - struct monitor_host * next; + struct host_entry * next; }; /* Globals */ /* Since the program is based around signals, a linked list of hosts is maintained here. */ - static struct monitor_host * hosts = NULL; + static struct host_entry * first_host_in_list = NULL; /* Set by command line flags. */ static bool verbose = false; static bool retry_down_cmd = false; - /* TODO: Get rid of this global. */ - static int send_delay = 1; /* - * 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(const 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); } /* - * Subtracts two timeval structs. - * Ensure out >= in. - * Modifies out = out - in. + * Calculate difference (a-b) between two timeval structs. */ -static void -tv_sub(register struct timeval * out, register struct timeval * in) +void +timeval_diff(struct timeval * a, const struct timeval * b) { - if ((out->tv_usec -= in->tv_usec) < 0) { - --out->tv_sec; - out->tv_usec += 1000000; + if (a->tv_usec < b->tv_usec) { + a->tv_sec--; + a->tv_usec += 1000000; } - out->tv_sec -= in->tv_sec; + a->tv_usec -= b->tv_usec; + a->tv_sec -= b->tv_sec; } /* - * Compose and transmit an ICMP ECHO REQUEST packet. The IP packet - * will be added on by the kernel. The ID field is our UNIX process ID, - * and the sequence number is an ascending integer. The first 8 bytes - * of the data portion are used to hold a UNIX "timeval" struct in VAX - * byte-order, to compute the round-trip time. + * This function iterates over the list of hosts, pinging any which are due. */ -static void -pinger(int ignore) +void +pinger(int ignore) /* Dummy parameter since this function registers as a signal handler. */ { - int i; - struct icmp * icp; - struct monitor_host * p = hosts; - u_char outpack[MAXPACKETSIZE]; - - while (p) { - if (p->socket != -1) { - struct timeval now; - - gettimeofday(&now, (struct timezone *) NULL); - tv_sub(&now, &p->last_ping_received); - - if (now.tv_sec > (p->max_delay + p->ping_interval)) { - if ((p->host_up) || retry_down_cmd) { - if (verbose) printf("INFO: Host %s stopped responding. Executing DOWN command.\n", p->name); - p->host_up = false; - if (!fork()) { - system(p->down_cmd); - exit(EXIT_SUCCESS); - } else { - wait(NULL); - } - } - } + assert(first_host_in_list); - gettimeofday(&now, (struct timezone *) NULL); - tv_sub(&now, &p->last_ping_sent); + struct icmp * icmp_packet; + struct host_entry * host = first_host_in_list; + unsigned char packet[IP_PACKET_MAX_BYTES]; /* Use char so this can be aliased later. */ - if (now.tv_sec > p->ping_interval) { /* Time to send ping */ - icp = (struct icmp *) outpack; - icp->icmp_type = ICMP_ECHO; - icp->icmp_code = 0; - icp->icmp_cksum = 0; - icp->icmp_seq = p->socket; - icp->icmp_id = getpid() & 0xFFFF; + while (host) { + struct timeval elapsed_time; + gettimeofday(&elapsed_time, NULL); + timeval_diff(&elapsed_time, &host->last_ping_received); - if (verbose) printf("INFO: Sending ICMP packet to %s.\n", p->name); + if ((elapsed_time.tv_sec > host->max_delay) && (host->host_up || retry_down_cmd)) { + if (verbose) printf("INFO: Host %s stopped responding. Executing DOWN command.\n", host->name); + host->host_up = false; + if (!fork()) { + system(host->down_cmd); + exit(EXIT_SUCCESS); + } + } - gettimeofday((struct timeval *) &outpack[8], (struct timezone *) NULL); + if (elapsed_time.tv_sec > host->ping_interval) { + if (verbose) printf("INFO: Sending ICMP packet to %s.\n", host->name); - int cc = DEFAULTDATALEN + 8; /* skips ICMP portion */ + icmp_packet = (struct icmp *) packet; + icmp_packet->icmp_type = ICMP_ECHO; + icmp_packet->icmp_code = 0; + icmp_packet->icmp_cksum = 0; + icmp_packet->icmp_seq = host->socket; + icmp_packet->icmp_id = getpid() & 0xFFFF; - /* compute ICMP checksum */ - icp->icmp_cksum = in_cksum((unsigned short *) icp, cc); + /* Write a timestamp struct in the packet's data segment for use in calculating travel times. */ + gettimeofday((struct timeval *) &packet[ICMP_ECHO_HEADER_BYTES], NULL); - i = sendto(p->socket, (char *) outpack, cc, 0, (const struct sockaddr *) (&p->dest), sizeof(struct sockaddr)); + icmp_packet->icmp_cksum = checksum((uint16_t *) packet); - gettimeofday(&p->last_ping_sent, (struct timezone *) NULL); + size_t bytes_sent = sendto(host->socket, packet, ICMP_ECHO_PACKET_BYTES, 0, + (const struct sockaddr *) &host->dest, + sizeof(struct sockaddr)); - if (i < 0 || i != cc) { - if (i<0) fprintf(stderr, "WARN: Failed sending ICMP packet to %s.\n", p->name); - } + if (bytes_sent == ICMP_ECHO_PACKET_BYTES) { + gettimeofday(&host->last_ping_sent, NULL); + } else { + fprintf(stderr, "WARN: Failed sending ICMP packet to %s.\n", host->name); } } - p = p->next; + host = host->next; } - signal(SIGALRM, pinger); /* restore handler */ - alarm(send_delay); + signal(SIGALRM, pinger); + alarm(TIMER_RESOLUTION); } -static void -read_icmp_data(struct monitor_host * p) +void +read_icmp_data(struct host_entry * host) { - int cc, iphdrlen, delay; - socklen_t fromlen; - struct sockaddr_in from; - struct ip * ip; - struct icmp * icmp; - struct timeval tv; - unsigned char buf[MAXPACKETSIZE]; + struct timeval now; + gettimeofday(&now, NULL); - gettimeofday(&tv, (struct timezone *) NULL); - - fromlen = sizeof(from); - if ((cc = recvfrom(p->socket, buf, sizeof(buf), 0, (struct sockaddr *)&from, &fromlen)) < 0) { - if (errno != EINTR) fprintf(stderr, "WARN: Error reading ICMP data from %s.\n", p->name); + struct sockaddr_in from; + socklen_t fromlen = sizeof(from); + int bytes; + unsigned char packet[IP_PACKET_MAX_BYTES]; /* Use char so this can be aliased later. */ + if ((bytes = recvfrom(host->socket, packet, sizeof(packet), 0, (struct sockaddr *) &from, &fromlen)) < 0) { + if (errno != EINTR) fprintf(stderr, "WARN: Error reading ICMP data from %s.\n", host->name); return; } - /* check IP header actual len */ - ip = (struct ip *) buf; - iphdrlen = ip->ip_hl << 2; - icmp = (struct icmp *) (buf + iphdrlen); + struct ip * ip = (struct ip *) packet; + int iphdrlen = ip->ip_hl << 2; + struct icmp * icmp = (struct icmp *) (packet + iphdrlen); - if (cc < iphdrlen + ICMP_MINLEN) { - fprintf(stderr, "WARN: Received short packet from %s.\n", p->name); + if (bytes < iphdrlen + ICMP_MINLEN) { + fprintf(stderr, "WARN: Received short packet from %s.\n", host->name); return; } - if (icmp->icmp_type == ICMP_ECHOREPLY && icmp->icmp_id == (getpid() & 0xFFFF) && icmp->icmp_seq == p->socket) { - - memcpy(&p->last_ping_received, &tv, sizeof(tv)); - - tv_sub(&tv, (struct timeval *) &icmp->icmp_data[0]); - delay = tv.tv_sec * 1000 + (tv.tv_usec / 1000); - - if (verbose) printf("INFO: Got ICMP reply from %s in %d ms.\n", p->name, delay); - if (!p->host_up) { - if (verbose) printf("INFO: Host %s started responding. Executing UP command.\n", p->name); - p->host_up = true; + if (icmp->icmp_type == ICMP_ECHOREPLY && icmp->icmp_id == (getpid() & 0xFFFF) && icmp->icmp_seq == host->socket) { + memcpy(&host->last_ping_received, &now, sizeof(now)); + if (verbose) printf("INFO: Got ICMP reply from %s.\n", host->name); + if (!host->host_up) { + if (verbose) printf("INFO: Host %s started responding. Executing UP command.\n", host->name); + host->host_up = true; if (!fork()) { - system(p->up_cmd); + system(host->up_cmd); exit(EXIT_SUCCESS); - } else { - wait(NULL); } } } else { - /* TODO: Do anything here? */ + /* The packet isn't what we expected. Ignore it and move on. */ } } -static void +/* + * This function contains the main program loop, listening for replies to pings + * sent from the signal-driven pinger(). + */ +void get_response(void) { - fd_set rfds; - int retval, maxd = -1; - struct monitor_host * p; - - while (1) { - p = hosts; + while (true) { + fd_set rfds; FD_ZERO(&rfds); - while (p) { - if (p->socket != -1) { - if (p->socket > maxd) maxd = p->socket; - FD_SET(p->socket, &rfds); - } - p = p->next; + + assert(first_host_in_list); + struct host_entry * host = first_host_in_list; + + int max_fd = -1; + while (host) { + if (host->socket > max_fd) max_fd = host->socket; + FD_SET(host->socket, &rfds); + host = host->next; } - retval = select(maxd+1, &rfds, NULL, NULL, NULL); - if (retval < 0) { - /* Intentionally empty. We arrive here when interrupted by a signal. No action should be taken. */ - } else { - if (retval > 0) { - p = hosts; - while (p) { - if (p->socket!=-1 && FD_ISSET(p->socket, &rfds)) read_icmp_data(p); - p = p->next; - } - } else { - /* TODO: How to handle this error? */ + int retval; + if ((retval = select(max_fd+1, &rfds, NULL, NULL, NULL)) > 0) { + assert(first_host_in_list); + host = first_host_in_list; + while (host) { + if (FD_ISSET(host->socket, &rfds)) read_icmp_data(host); + host = host->next; } + } else { + /* An error or interruption occurred. */ + /* We can't do anything about it, so loop and try again. */ } } } -static void +/* + * Parse a configuration file using the `iniparser` library. + * See `icmpmonitor.ini` and `README.md` for examples and reference. + */ +void parse_config(const char * conf_file) { dictionary * conf = iniparser_load(conf_file); @@ -289,42 +266,41 @@ parse_config(const char * conf_file) exit(EXIT_FAILURE); } - struct monitor_host * host_list_end = NULL; + struct host_entry * host_list_end = NULL; for (int i=0; i < host_count; i++) { /* Allocate a reusable buffer large enough to hold the full 'section:key' string. */ int section_len = strlen(iniparser_getsecname(conf, i)); - char * key_buf = malloc(section_len + 1 + MAXCONFKEYLEN + 1); + char * key_buf = malloc(section_len + 1 + MAX_CONF_KEY_LEN + 1); /* +1 for ':' and '\0' */ strcpy(key_buf, iniparser_getsecname(conf, i)); key_buf[section_len++] = ':'; - struct monitor_host * cur_host = malloc(sizeof(struct monitor_host)); + struct host_entry * cur_host = malloc(sizeof(struct host_entry)); key_buf[section_len] = '\0'; - strncat(key_buf, "host", MAXCONFKEYLEN); + strncat(key_buf, "host", MAX_CONF_KEY_LEN); cur_host->name = strdup(iniparser_getstring(conf, key_buf, NULL)); key_buf[section_len] = '\0'; - strncat(key_buf, "interval", MAXCONFKEYLEN); + strncat(key_buf, "interval", MAX_CONF_KEY_LEN); cur_host->ping_interval = iniparser_getint(conf, key_buf, -1); key_buf[section_len] = '\0'; - strncat(key_buf, "max_delay", MAXCONFKEYLEN); + strncat(key_buf, "max_delay", MAX_CONF_KEY_LEN); cur_host->max_delay = iniparser_getint(conf, key_buf, -1); key_buf[section_len] = '\0'; - strncat(key_buf, "up_cmd", MAXCONFKEYLEN); + strncat(key_buf, "up_cmd", MAX_CONF_KEY_LEN); cur_host->up_cmd = strdup(iniparser_getstring(conf, key_buf, NULL)); key_buf[section_len] = '\0'; - strncat(key_buf, "down_cmd", MAXCONFKEYLEN); + strncat(key_buf, "down_cmd", MAX_CONF_KEY_LEN); cur_host->down_cmd = strdup(iniparser_getstring(conf, key_buf, NULL)); key_buf[section_len] = '\0'; - /* TODO: Parse for up/down/auto in start_condition. */ - /* TODO: Do a host up/down check if necessary. */ - cur_host->host_up = true; + strncat(key_buf, "start_condition", MAX_CONF_KEY_LEN); + const char * value = iniparser_getstring(conf, key_buf, NULL); + if (value) cur_host->host_up = *value == 'u' ? true : false; - /* TODO: Do I want to make any checks for start_condition? */ if (cur_host->name == NULL || cur_host->ping_interval == -1 || cur_host->max_delay == -1) { fprintf(stderr, "ERROR: Problems parsing section %s.\n", iniparser_getsecname(conf, i)); exit(EXIT_FAILURE); @@ -334,8 +310,8 @@ parse_config(const char * conf_file) cur_host->next = NULL; gettimeofday(&(cur_host->last_ping_received), (struct timezone *) NULL); - if (hosts == NULL) { - hosts = cur_host; + if (first_host_in_list == NULL) { + first_host_in_list = cur_host; host_list_end = cur_host; } else { host_list_end->next = cur_host; @@ -347,62 +323,84 @@ parse_config(const char * conf_file) iniparser_freedict(conf); } -static int +/* + * Parse string (IP or hostname) to Internet address. + * + * Returns 0 if host can't be resolved, otherwise returns an Internet address. + */ +uint32_t get_host_addr(const char * name) { - static int res; - struct hostent * host_ent; - - if ((res = inet_addr(name)) < 0) { - host_ent = gethostbyname(name); - if (!host_ent) return -1; - memcpy(&res, host_ent->h_addr, host_ent->h_length); - } - return(res); + struct addrinfo hints; + memset(&hints, 0, sizeof(hints)); + hints.ai_family = AF_INET; + + int rv; + struct addrinfo * address; + if ((rv = getaddrinfo(name, NULL, &hints, &address)) != 0) return 0; + uint32_t result = ((struct sockaddr_in *)(address->ai_addr))->sin_addr.s_addr; + freeaddrinfo(address); + return result; } -static int -gcd(int x, int y) +size_t +gcd(const size_t x, const size_t y) { - int remainder = x % y; + size_t remainder = x % y; if (remainder == 0) return y; return gcd(y, remainder); } -static void +void +remove_host_from_list(struct host_entry * host) +{ + assert(first_host_in_list); + assert(host); + + if (host == first_host_in_list) { + first_host_in_list = host->next; + } else { + struct host_entry * temp = first_host_in_list; + while (temp->next != host && temp->next != NULL) temp = temp->next; + if (temp->next == NULL) return; + temp->next = temp->next->next; + } + free(host); +} + +void init_hosts(void) { - struct monitor_host * p = hosts; + struct host_entry * host; struct protoent * proto; - int ok = 0; if ((proto = getprotobyname("icmp")) == NULL) { fprintf(stderr, "ERROR: Unknown protocol: icmp.\n"); exit(EXIT_FAILURE); } - while (p) { - bzero(&p->dest, sizeof(p->dest)); - p->dest.sin_family = AF_INET; - if ((p->dest.sin_addr.s_addr = get_host_addr(p->name)) <= 0) { - fprintf(stderr, "WARN: Can't resolve host. Skipping client %s.\n", p->name); - p->socket=-1; - } else { - if ((p->socket = socket(AF_INET,SOCK_RAW,proto->p_proto)) < 0) { - fprintf(stderr, "WARN: Can't create socket. Skipping client %s.\n", p->name); - p->socket=-1; - } else { - if (ok == 0) send_delay = p->ping_interval; - else send_delay = gcd(send_delay, p->ping_interval); - ok++; - } + assert(first_host_in_list); + host = first_host_in_list; + while (host) { + struct host_entry * next_host = host->next; + bzero(&host->dest, sizeof(host->dest)); + host->dest.sin_family = AF_INET; + if (!(host->dest.sin_addr.s_addr = get_host_addr(host->name))) { + fprintf(stderr, "WARN: Removing unresolvable host %s from list.\n", host->name); + remove_host_from_list(host); } - p = p->next; + host = next_host; } - if (!ok) { - fprintf(stderr, "ERROR: No hosts left to process.\n"); - exit(EXIT_FAILURE); + assert(first_host_in_list); + host = first_host_in_list; + while (host) { + struct host_entry * next_host = host->next; + if ((host->socket = socket(AF_INET, SOCK_RAW, proto->p_proto)) < 0) { + fprintf(stderr, "WARN: Failed creating socket. Removing host %s from list.\n", host->name); + remove_host_from_list(host); + } + host = next_host; } } @@ -441,7 +439,7 @@ parse_params(int argc, char ** argv) break; } } - if (hosts == NULL) { + if (first_host_in_list == NULL) { fprintf(stderr, "ERROR: Unable to parse a config file.\n"); exit(EXIT_FAILURE); } @@ -455,7 +453,7 @@ main(int argc, char ** argv) init_hosts(); signal(SIGALRM, pinger); - alarm(send_delay); + alarm(TIMER_RESOLUTION); get_response();