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monitoring-plugins/plugins/check_dns.c
Lorenz Kästle 802e46f8ea Run clang-format again
2025-09-15 12:59:37 +02:00

672 lines
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/*****************************************************************************
*
* Monitoring check_dns plugin
*
* License: GPL
* Copyright (c) 2000-2024 Monitoring Plugins Development Team
*
* Description:
*
* This file contains the check_dns plugin
*
* LIMITATION: nslookup on Solaris 7 can return output over 2 lines, which
* will not be picked up by this plugin
*
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*
*****************************************************************************/
const char *progname = "check_dns";
const char *copyright = "2000-2024";
const char *email = "devel@monitoring-plugins.org";
#include "common.h"
#include "utils.h"
#include "utils_base.h"
#include "netutils.h"
#include "runcmd.h"
#include "states.h"
#include "check_dns.d/config.h"
typedef struct {
int errorcode;
check_dns_config config;
} check_dns_config_wrapper;
static check_dns_config_wrapper process_arguments(int /*argc*/, char ** /*argv*/);
static check_dns_config_wrapper validate_arguments(check_dns_config_wrapper /*config_wrapper*/);
static mp_state_enum error_scan(char * /*input_buffer*/, bool * /*is_nxdomain*/,
const char /*dns_server*/[ADDRESS_LENGTH]);
static bool ip_match_cidr(const char * /*addr*/, const char * /*cidr_ro*/);
static unsigned long ip2long(const char * /*src*/);
static void print_help(void);
void print_usage(void);
static bool verbose = false;
static int qstrcmp(const void *p1, const void *p2) {
/* The actual arguments to this function are "pointers to
pointers to char", but strcmp() arguments are "pointers
to char", hence the following cast plus dereference */
return strcmp(*(char *const *)p1, *(char *const *)p2);
}
int main(int argc, char **argv) {
setlocale(LC_ALL, "");
bindtextdomain(PACKAGE, LOCALEDIR);
textdomain(PACKAGE);
/* Set signal handling and alarm */
if (signal(SIGALRM, runcmd_timeout_alarm_handler) == SIG_ERR) {
usage_va(_("Cannot catch SIGALRM"));
}
/* Parse extra opts if any */
argv = np_extra_opts(&argc, argv, progname);
check_dns_config_wrapper tmp = process_arguments(argc, argv);
if (tmp.errorcode == ERROR) {
usage_va(_("Could not parse arguments"));
}
const check_dns_config config = tmp.config;
char *command_line = NULL;
/* get the command to run */
xasprintf(&command_line, "%s %s %s", NSLOOKUP_COMMAND, config.query_address, config.dns_server);
struct timeval tv;
alarm(timeout_interval);
gettimeofday(&tv, NULL);
if (verbose) {
printf("%s\n", command_line);
}
output chld_out;
output chld_err;
char *msg = NULL;
mp_state_enum result = STATE_UNKNOWN;
/* run the command */
if ((np_runcmd(command_line, &chld_out, &chld_err, 0)) != 0) {
msg = (char *)_("nslookup returned an error status");
result = STATE_WARNING;
}
/* =====
* scan stdout, main results get retrieved here
* =====
*/
char *address = NULL; /* comma separated str with addrs/ptrs (sorted) */
char **addresses = NULL; // All addresses parsed from stdout
size_t n_addresses = 0; // counter for retrieved addresses
bool non_authoritative = false;
bool is_nxdomain = false;
bool parse_address = false; /* This flag scans for Address: but only after Name: */
for (size_t i = 0; i < chld_out.lines; i++) {
if (addresses == NULL) {
addresses = malloc(sizeof(*addresses) * 10);
} else if (!(n_addresses % 10)) {
addresses = realloc(addresses, sizeof(*addresses) * (n_addresses + 10));
}
if (verbose) {
puts(chld_out.line[i]);
}
if (strcasestr(chld_out.line[i], ".in-addr.arpa") ||
strcasestr(chld_out.line[i], ".ip6.arpa")) {
if ((strstr(chld_out.line[i], "canonical name = ") != NULL)) {
continue;
}
char *temp_buffer = NULL;
if ((temp_buffer = strstr(chld_out.line[i], "name = "))) {
addresses[n_addresses++] = strdup(temp_buffer + 7);
} else {
msg = (char *)_("Warning plugin error");
result = STATE_WARNING;
}
}
/* bug ID: 2946553 - Older versions of bind will use all available dns
servers, we have to match the one specified */
if (strstr(chld_out.line[i], "Server:") && strlen(config.dns_server) > 0) {
char *temp_buffer = strchr(chld_out.line[i], ':');
if (temp_buffer == NULL) {
die(STATE_UNKNOWN, _("'%s' returned a weirdly formatted Server line\n"),
NSLOOKUP_COMMAND);
}
temp_buffer++;
/* Strip leading tabs */
for (; *temp_buffer != '\0' && *temp_buffer == '\t'; temp_buffer++) {
/* NOOP */;
}
strip(temp_buffer);
if (strlen(temp_buffer) == 0) {
die(STATE_CRITICAL, _("DNS CRITICAL - '%s' returned empty server string\n"),
NSLOOKUP_COMMAND);
}
if (strcmp(temp_buffer, config.dns_server) != 0) {
die(STATE_CRITICAL, _("DNS CRITICAL - No response from DNS %s\n"),
config.dns_server);
}
}
/* the server is responding, we just got the host name... */
if (strstr(chld_out.line[i], "Name:")) {
parse_address = true;
} else if (parse_address && (strstr(chld_out.line[i], "Address:") ||
strstr(chld_out.line[i], "Addresses:"))) {
char *temp_buffer = strchr(chld_out.line[i], ':');
if (temp_buffer == NULL) {
die(STATE_UNKNOWN, _("'%s' returned a weirdly formatted Address line\n"),
NSLOOKUP_COMMAND);
}
temp_buffer++;
/* Strip leading spaces */
while (*temp_buffer == ' ') {
temp_buffer++;
}
strip(temp_buffer);
if (strlen(temp_buffer) == 0) {
die(STATE_CRITICAL, _("DNS CRITICAL - '%s' returned empty host name string\n"),
NSLOOKUP_COMMAND);
}
addresses[n_addresses++] = strdup(temp_buffer);
} else if (strstr(chld_out.line[i], _("Non-authoritative answer:"))) {
non_authoritative = true;
}
result = error_scan(chld_out.line[i], &is_nxdomain, config.dns_server);
if (result != STATE_OK) {
msg = strchr(chld_out.line[i], ':');
if (msg) {
msg++;
}
break;
}
}
char input_buffer[MAX_INPUT_BUFFER];
/* scan stderr */
for (size_t i = 0; i < chld_err.lines; i++) {
if (verbose) {
puts(chld_err.line[i]);
}
if (error_scan(chld_err.line[i], &is_nxdomain, config.dns_server) != STATE_OK) {
result =
max_state(result, error_scan(chld_err.line[i], &is_nxdomain, config.dns_server));
msg = strchr(input_buffer, ':');
if (msg) {
msg++;
} else {
msg = input_buffer;
}
}
}
if (is_nxdomain && !config.expect_nxdomain) {
die(STATE_CRITICAL, _("Domain '%s' was not found by the server\n"), config.query_address);
}
if (addresses) {
size_t slen = 1;
char *adrp = NULL;
qsort(addresses, n_addresses, sizeof(*addresses), qstrcmp);
for (size_t i = 0; i < n_addresses; i++) {
slen += strlen(addresses[i]) + 1;
}
// Temporary pointer adrp gets moved, address stays on the beginning
adrp = address = malloc(slen);
for (size_t i = 0; i < n_addresses; i++) {
if (i) {
*adrp++ = ',';
}
strcpy(adrp, addresses[i]);
adrp += strlen(addresses[i]);
}
*adrp = 0;
} else {
die(STATE_CRITICAL, _("DNS CRITICAL - '%s' msg parsing exited with no address\n"),
NSLOOKUP_COMMAND);
}
/* compare to expected address */
if (result == STATE_OK && config.expected_address_cnt > 0) {
result = STATE_CRITICAL;
char *temp_buffer = "";
unsigned long expect_match = (1 << config.expected_address_cnt) - 1;
unsigned long addr_match = (1 << n_addresses) - 1;
for (size_t i = 0; i < config.expected_address_cnt; i++) {
/* check if we get a match on 'raw' ip or cidr */
for (size_t j = 0; j < n_addresses; j++) {
if (strcmp(addresses[j], config.expected_address[i]) == 0 ||
ip_match_cidr(addresses[j], config.expected_address[i])) {
result = STATE_OK;
addr_match &= ~(1 << j);
expect_match &= ~(1 << i);
}
}
/* prepare an error string */
xasprintf(&temp_buffer, "%s%s; ", temp_buffer, config.expected_address[i]);
}
/* check if expected_address must cover all in addresses and none may be missing */
if (config.all_match && (expect_match != 0 || addr_match != 0)) {
result = STATE_CRITICAL;
}
if (result == STATE_CRITICAL) {
/* Strip off last semicolon... */
temp_buffer[strlen(temp_buffer) - 2] = '\0';
xasprintf(&msg, _("expected '%s' but got '%s'"), temp_buffer, address);
}
}
if (config.expect_nxdomain) {
if (!is_nxdomain) {
result = STATE_CRITICAL;
xasprintf(&msg, _("Domain '%s' was found by the server: '%s'\n"), config.query_address,
address);
} else {
if (address != NULL) {
free(address);
}
address = "NXDOMAIN";
}
}
/* check if authoritative */
if (result == STATE_OK && config.expect_authority && non_authoritative) {
result = STATE_CRITICAL;
xasprintf(&msg, _("server %s is not authoritative for %s"), config.dns_server,
config.query_address);
}
long microsec = deltime(tv);
double elapsed_time = (double)microsec / 1.0e6;
if (result == STATE_OK) {
result = get_status(elapsed_time, config.time_thresholds);
if (result == STATE_OK) {
printf("DNS %s: ", _("OK"));
} else if (result == STATE_WARNING) {
printf("DNS %s: ", _("WARNING"));
} else if (result == STATE_CRITICAL) {
printf("DNS %s: ", _("CRITICAL"));
}
printf(ngettext("%.3f second response time", "%.3f seconds response time", elapsed_time),
elapsed_time);
printf(_(". %s returns %s"), config.query_address, address);
if ((config.time_thresholds->warning != NULL) &&
(config.time_thresholds->critical != NULL)) {
printf("|%s\n",
fperfdata("time", elapsed_time, "s", true, config.time_thresholds->warning->end,
true, config.time_thresholds->critical->end, true, 0, false, 0));
} else if ((config.time_thresholds->warning == NULL) &&
(config.time_thresholds->critical != NULL)) {
printf("|%s\n", fperfdata("time", elapsed_time, "s", false, 0, true,
config.time_thresholds->critical->end, true, 0, false, 0));
} else if ((config.time_thresholds->warning != NULL) &&
(config.time_thresholds->critical == NULL)) {
printf("|%s\n",
fperfdata("time", elapsed_time, "s", true, config.time_thresholds->warning->end,
false, 0, true, 0, false, 0));
} else {
printf("|%s\n",
fperfdata("time", elapsed_time, "s", false, 0, false, 0, true, 0, false, 0));
}
} else if (result == STATE_WARNING) {
printf(_("DNS WARNING - %s\n"),
!strcmp(msg, "") ? _(" Probably a non-existent host/domain") : msg);
} else if (result == STATE_CRITICAL) {
printf(_("DNS CRITICAL - %s\n"),
!strcmp(msg, "") ? _(" Probably a non-existent host/domain") : msg);
} else {
printf(_("DNS UNKNOWN - %s\n"),
!strcmp(msg, "") ? _(" Probably a non-existent host/domain") : msg);
}
exit(result);
}
bool ip_match_cidr(const char *addr, const char *cidr_ro) {
char *subnet;
char *mask_c;
char *cidr = strdup(cidr_ro);
int mask;
subnet = strtok(cidr, "/");
mask_c = strtok(NULL, "\0");
if (!subnet || !mask_c) {
return false;
}
mask = atoi(mask_c);
/* https://www.cryptobells.com/verifying-ips-in-a-subnet-in-php/ */
return (ip2long(addr) & ~((1 << (32 - mask)) - 1)) == (ip2long(subnet) >> (32 - mask))
<< (32 - mask);
}
unsigned long ip2long(const char *src) {
unsigned long ip[4];
/* http://computer-programming-forum.com/47-c-language/1376ffb92a12c471.htm */
return (sscanf(src, "%3lu.%3lu.%3lu.%3lu", &ip[0], &ip[1], &ip[2], &ip[3]) == 4 &&
ip[0] < 256 && ip[1] < 256 && ip[2] < 256 && ip[3] < 256)
? ip[0] << 24 | ip[1] << 16 | ip[2] << 8 | ip[3]
: 0;
}
mp_state_enum error_scan(char *input_buffer, bool *is_nxdomain,
const char dns_server[ADDRESS_LENGTH]) {
const int nxdomain = strstr(input_buffer, "Non-existent") ||
strstr(input_buffer, "** server can't find") ||
strstr(input_buffer, "** Can't find") || strstr(input_buffer, "NXDOMAIN");
if (nxdomain) {
*is_nxdomain = true;
}
/* the DNS lookup timed out */
if (strstr(input_buffer,
_("Note: nslookup is deprecated and may be removed from future releases.")) ||
strstr(input_buffer,
_("Consider using the `dig' or `host' programs instead. Run nslookup with")) ||
strstr(input_buffer, _("the `-sil[ent]' option to prevent this message from appearing."))) {
return STATE_OK;
}
/* DNS server is not running... */
else if (strstr(input_buffer, "No response from server")) {
die(STATE_CRITICAL, _("No response from DNS %s\n"), dns_server);
} else if (strstr(input_buffer, "no servers could be reached")) {
die(STATE_CRITICAL, _("No response from DNS %s\n"), dns_server);
}
/* Host name is valid, but server doesn't have records... */
else if (strstr(input_buffer, "No records")) {
die(STATE_CRITICAL, _("DNS %s has no records\n"), dns_server);
}
/* Connection was refused */
else if (strstr(input_buffer, "Connection refused") ||
strstr(input_buffer, "Couldn't find server") || strstr(input_buffer, "Refused") ||
(strstr(input_buffer, "** server can't find") && strstr(input_buffer, ": REFUSED"))) {
die(STATE_CRITICAL, _("Connection to DNS %s was refused\n"), dns_server);
}
/* Query refused (usually by an ACL in the namserver) */
else if (strstr(input_buffer, "Query refused")) {
die(STATE_CRITICAL, _("Query was refused by DNS server at %s\n"), dns_server);
}
/* No information (e.g. nameserver IP has two PTR records) */
else if (strstr(input_buffer, "No information")) {
die(STATE_CRITICAL, _("No information returned by DNS server at %s\n"), dns_server);
}
/* Network is unreachable */
else if (strstr(input_buffer, "Network is unreachable")) {
die(STATE_CRITICAL, _("Network is unreachable\n"));
}
/* Internal server failure */
else if (strstr(input_buffer, "Server failure")) {
die(STATE_CRITICAL, _("DNS failure for %s\n"), dns_server);
}
/* Request error or the DNS lookup timed out */
else if (strstr(input_buffer, "Format error") || strstr(input_buffer, "Timed out")) {
return STATE_WARNING;
}
return STATE_OK;
}
/* process command-line arguments */
check_dns_config_wrapper process_arguments(int argc, char **argv) {
static struct option long_opts[] = {{"help", no_argument, 0, 'h'},
{"version", no_argument, 0, 'V'},
{"verbose", no_argument, 0, 'v'},
{"timeout", required_argument, 0, 't'},
{"hostname", required_argument, 0, 'H'},
{"server", required_argument, 0, 's'},
{"reverse-server", required_argument, 0, 'r'},
{"expected-address", required_argument, 0, 'a'},
{"expect-nxdomain", no_argument, 0, 'n'},
{"expect-authority", no_argument, 0, 'A'},
{"all", no_argument, 0, 'L'},
{"warning", required_argument, 0, 'w'},
{"critical", required_argument, 0, 'c'},
{0, 0, 0, 0}};
check_dns_config_wrapper result = {
.config = check_dns_config_init(),
.errorcode = OK,
};
if (argc < 2) {
result.errorcode = ERROR;
return result;
}
for (int index = 1; index < argc; index++) {
if (strcmp("-to", argv[index]) == 0) {
strcpy(argv[index], "-t");
}
}
char *warning = NULL;
char *critical = NULL;
int opt_index = 0;
int index = 0;
while (true) {
index = getopt_long(argc, argv, "hVvALnt:H:s:r:a:w:c:", long_opts, &opt_index);
if (index == -1 || index == EOF) {
break;
}
switch (index) {
case 'h': /* help */
print_help();
exit(STATE_UNKNOWN);
case 'V': /* version */
print_revision(progname, NP_VERSION);
exit(STATE_UNKNOWN);
case 'v': /* version */
verbose = true;
break;
case 't': /* timeout period */
timeout_interval = atoi(optarg);
break;
case 'H': /* hostname */
if (strlen(optarg) >= ADDRESS_LENGTH) {
die(STATE_UNKNOWN, _("Input buffer overflow\n"));
}
strcpy(result.config.query_address, optarg);
break;
case 's': /* server name */
/* TODO: this host_or_die check is probably unnecessary.
* Better to confirm nslookup response matches */
host_or_die(optarg);
if (strlen(optarg) >= ADDRESS_LENGTH) {
die(STATE_UNKNOWN, _("Input buffer overflow\n"));
}
strcpy(result.config.dns_server, optarg);
break;
case 'r': /* reverse server name */
/* TODO: Is this host_or_die necessary? */
// TODO This does not do anything!!! 2025-03-08 rincewind
host_or_die(optarg);
if (strlen(optarg) >= ADDRESS_LENGTH) {
die(STATE_UNKNOWN, _("Input buffer overflow\n"));
}
static char ptr_server[ADDRESS_LENGTH] = "";
strcpy(ptr_server, optarg);
break;
case 'a': /* expected address */
if (strlen(optarg) >= ADDRESS_LENGTH) {
die(STATE_UNKNOWN, _("Input buffer overflow\n"));
}
if (strchr(optarg, ',') != NULL) {
char *comma = strchr(optarg, ',');
while (comma != NULL) {
result.config.expected_address = (char **)realloc(
result.config.expected_address,
(result.config.expected_address_cnt + 1) * sizeof(char **));
result.config.expected_address[result.config.expected_address_cnt] =
strndup(optarg, comma - optarg);
result.config.expected_address_cnt++;
optarg = comma + 1;
comma = strchr(optarg, ',');
}
result.config.expected_address =
(char **)realloc(result.config.expected_address,
(result.config.expected_address_cnt + 1) * sizeof(char **));
result.config.expected_address[result.config.expected_address_cnt] = strdup(optarg);
result.config.expected_address_cnt++;
} else {
result.config.expected_address =
(char **)realloc(result.config.expected_address,
(result.config.expected_address_cnt + 1) * sizeof(char **));
result.config.expected_address[result.config.expected_address_cnt] = strdup(optarg);
result.config.expected_address_cnt++;
}
break;
case 'n': /* expect NXDOMAIN */
result.config.expect_nxdomain = true;
break;
case 'A': /* expect authority */
result.config.expect_authority = true;
break;
case 'L': /* all must match */
result.config.all_match = true;
break;
case 'w':
warning = optarg;
break;
case 'c':
critical = optarg;
break;
default: /* args not parsable */
usage5();
}
}
index = optind;
if (strlen(result.config.query_address) == 0 && index < argc) {
if (strlen(argv[index]) >= ADDRESS_LENGTH) {
die(STATE_UNKNOWN, _("Input buffer overflow\n"));
}
strcpy(result.config.query_address, argv[index++]);
}
if (strlen(result.config.dns_server) == 0 && index < argc) {
/* TODO: See -s option */
host_or_die(argv[index]);
if (strlen(argv[index]) >= ADDRESS_LENGTH) {
die(STATE_UNKNOWN, _("Input buffer overflow\n"));
}
strcpy(result.config.dns_server, argv[index++]);
}
set_thresholds(&result.config.time_thresholds, warning, critical);
return validate_arguments(result);
}
check_dns_config_wrapper validate_arguments(check_dns_config_wrapper config_wrapper) {
if (config_wrapper.config.query_address[0] == 0) {
printf("missing --host argument\n");
config_wrapper.errorcode = ERROR;
return config_wrapper;
}
if (config_wrapper.config.expected_address_cnt > 0 && config_wrapper.config.expect_nxdomain) {
printf("--expected-address and --expect-nxdomain cannot be combined\n");
config_wrapper.errorcode = ERROR;
return config_wrapper;
}
return config_wrapper;
}
void print_help(void) {
print_revision(progname, NP_VERSION);
printf("Copyright (c) 1999 Ethan Galstad <nagios@nagios.org>\n");
printf(COPYRIGHT, copyright, email);
printf("%s\n", _("This plugin uses the nslookup program to obtain the IP address for the given "
"host/domain query."));
printf("%s\n", _("An optional DNS server to use may be specified."));
printf("%s\n", _("If no DNS server is specified, the default server(s) specified in "
"/etc/resolv.conf will be used."));
printf("\n\n");
print_usage();
printf(UT_HELP_VRSN);
printf(UT_EXTRA_OPTS);
printf(" -H, --hostname=HOST\n");
printf(" %s\n", _("The name or address you want to query"));
printf(" -s, --server=HOST\n");
printf(" %s\n", _("Optional DNS server you want to use for the lookup"));
printf(" -a, --expected-address=IP-ADDRESS|CIDR|HOST\n");
printf(" %s\n",
_("Optional IP-ADDRESS/CIDR you expect the DNS server to return. HOST must end"));
printf(" %s\n",
_("with a dot (.). This option can be repeated multiple times (Returns OK if any"));
printf(" %s\n", _("value matches)."));
printf(" -n, --expect-nxdomain\n");
printf(" %s\n",
_("Expect the DNS server to return NXDOMAIN (i.e. the domain was not found)"));
printf(" %s\n", _("Cannot be used together with -a"));
printf(" -A, --expect-authority\n");
printf(" %s\n", _("Optionally expect the DNS server to be authoritative for the lookup"));
printf(" -w, --warning=seconds\n");
printf(" %s\n", _("Return warning if elapsed time exceeds value. Default off"));
printf(" -c, --critical=seconds\n");
printf(" %s\n", _("Return critical if elapsed time exceeds value. Default off"));
printf(" -L, --all\n");
printf(" %s\n",
_("Return critical if the list of expected addresses does not match all addresses"));
printf(" %s\n", _("returned. Default off"));
printf(UT_CONN_TIMEOUT, DEFAULT_SOCKET_TIMEOUT);
printf(UT_SUPPORT);
}
void print_usage(void) {
printf("%s\n", _("Usage:"));
printf("%s -H host [-s server] [-a expected-address] [-n] [-A] [-t timeout] [-w warn] [-c "
"crit] [-L]\n",
progname);
}
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