OpenBSD: pledge(2) some network-facing checks (#2225)

OpenBSD's pledge(2) system call allows the current process to
self-restrict itself, being reduced to promised pledges. For example,
unless a process says it wants to write to files, it is not allowed to
do so any longer.

This change starts by calling pledge(2) in some network-facing checks,
removing the more dangerous privileges, such as executing other files.

My initial motivation came from check_icmp, being installed as a setuid
binary and (temporarily) running with root privileges. There, the
pledge(2) calls result in check_icmp to only being allowed to interact
with the network and to setuid(2) to the calling user later on.

Afterwards, I went through my most commonly used monitoring plugins
directly interacting with the network. Thus, I continued with
pledge(2)-ing check_curl - having a huge codebase and all -,
check_ntp_time, check_smtp, check_ssh, and check_tcp.

For most of those, the changes were quite similar: start with
network-friendly promises, parse the configuration, give up file access,
and proceed with the actual check.

plugins-root/check_icmp.c

@@ -812,6 +812,15 @@ void parse_address(const struct sockaddr_storage *addr, char *dst, socklen_t siz
 }
 
 int main(int argc, char **argv) {
+#ifdef __OpenBSD__
+	/* - rpath is required to read --extra-opts (given up later)
+	 * - inet is required for sockets
+	 * - dns is required for name lookups (given up later)
+	 * - id is required for temporary privilege drops in configparsing and for
+	 *   permanent privilege dropping after opening the socket (given up later) */
+	pledge("stdio rpath inet dns id", NULL);
+#endif // __OpenBSD__
+
 	setlocale(LC_ALL, "");
 	bindtextdomain(PACKAGE, LOCALEDIR);
 	textdomain(PACKAGE);
@@ -836,6 +845,10 @@ int main(int argc, char **argv) {
 		crash("failed to parse config");
 	}
 
+#ifdef __OpenBSD__
+	pledge("stdio inet dns id", NULL);
+#endif // __OpenBSD__
+
 	const check_icmp_config config = tmp_config.config;
 
 	if (config.output_format_is_set) {
@@ -898,6 +911,10 @@ int main(int argc, char **argv) {
 		return 1;
 	}
 
+#ifdef __OpenBSD__
+	pledge("stdio inet", NULL);
+#endif // __OpenBSD__
+
 	if (sockset.socket4) {
 		int result = setsockopt(sockset.socket4, SOL_IP, IP_TTL, &config.ttl, sizeof(config.ttl));
 		if (debug) {

plugins/check_curl.c

@@ -120,6 +120,14 @@ mp_state_enum np_net_ssl_check_certificate(X509 *certificate, int days_till_exp_
 #endif /* defined(HAVE_SSL) && defined(USE_OPENSSL) */
 
 int main(int argc, char **argv) {
+#ifdef __OpenBSD__
+	/* - rpath is required to read --extra-opts, CA and/or client certs
+	 * - wpath is required to write --cookie-jar (possibly given up later)
+	 * - inet is required for sockets
+	 * - dns is required for name lookups */
+	pledge("stdio rpath wpath inet dns", NULL);
+#endif // __OpenBSD__
+
 	setlocale(LC_ALL, "");
 	bindtextdomain(PACKAGE, LOCALEDIR);
 	textdomain(PACKAGE);
@@ -135,6 +143,15 @@ int main(int argc, char **argv) {
 
 	const check_curl_config config = tmp_config.config;
 
+#ifdef __OpenBSD__
+	if (!config.curl_config.cookie_jar_file) {
+		if (verbose >= 2) {
+			printf(_("* No \"--cookie-jar\" is used, giving up \"wpath\" pledge(2)\n"));
+		}
+		pledge("stdio rpath inet dns", NULL);
+	}
+#endif // __OpenBSD__
+
 	if (config.output_format_is_set) {
 		mp_set_format(config.output_format);
 	}

plugins/check_ntp_time.c

@@ -661,6 +661,14 @@ static check_ntp_time_config_wrapper process_arguments(int argc, char **argv) {
 }
 
 int main(int argc, char *argv[]) {
+#ifdef __OpenBSD__
+	/* - rpath is required to read --extra-opts (given up later)
+	 * - inet is required for sockets
+	 * - unix is required for Unix domain sockets
+	 * - dns is required for name lookups */
+	pledge("stdio rpath inet unix dns", NULL);
+#endif // __OpenBSD__
+
 	setlocale(LC_ALL, "");
 	bindtextdomain(PACKAGE, LOCALEDIR);
 	textdomain(PACKAGE);
@@ -674,6 +682,10 @@ int main(int argc, char *argv[]) {
 		usage4(_("Could not parse arguments"));
 	}
 
+#ifdef __OpenBSD__
+	pledge("stdio inet unix dns", NULL);
+#endif // __OpenBSD__
+
 	const check_ntp_time_config config = tmp_config.config;
 
 	if (config.output_format_is_set) {

plugins/check_smtp.c

@@ -100,6 +100,14 @@ static int my_close(int /*socket_descriptor*/);
 static int verbose = 0;
 
 int main(int argc, char **argv) {
+#ifdef __OpenBSD__
+	/* - rpath is required to read --extra-opts (given up later)
+	 * - inet is required for sockets
+	 * - unix is required for Unix domain sockets
+	 * - dns is required for name lookups */
+	pledge("stdio rpath inet unix dns", NULL);
+#endif // __OpenBSD__
+
 	setlocale(LC_ALL, "");
 	bindtextdomain(PACKAGE, LOCALEDIR);
 	textdomain(PACKAGE);
@@ -113,6 +121,10 @@ int main(int argc, char **argv) {
 		usage4(_("Could not parse arguments"));
 	}
 
+#ifdef __OpenBSD__
+	pledge("stdio inet unix dns", NULL);
+#endif // __OpenBSD__
+
 	const check_smtp_config config = tmp_config.config;
 
 	if (config.output_format_is_set) {

plugins/check_ssh.c

@@ -61,6 +61,14 @@ static int ssh_connect(mp_check *overall, char *haddr, int hport, char *remote_v
 					   char *remote_protocol);
 
 int main(int argc, char **argv) {
+#ifdef __OpenBSD__
+	/* - rpath is required to read --extra-opts (given up later)
+	 * - inet is required for sockets
+	 * - unix is required for Unix domain sockets
+	 * - dns is required for name lookups */
+	pledge("stdio rpath inet unix dns", NULL);
+#endif // __OpenBSD__
+
 	setlocale(LC_ALL, "");
 	bindtextdomain(PACKAGE, LOCALEDIR);
 	textdomain(PACKAGE);
@@ -74,6 +82,10 @@ int main(int argc, char **argv) {
 		usage4(_("Could not parse arguments"));
 	}
 
+#ifdef __OpenBSD__
+	pledge("stdio inet unix dns", NULL);
+#endif // __OpenBSD__
+
 	check_ssh_config config = tmp_config.config;
 
 	mp_check overall = mp_check_init();

plugins/check_tcp.c

@@ -89,6 +89,14 @@ const int DEFAULT_NNTPS_PORT = 563;
 const int DEFAULT_CLAMD_PORT = 3310;
 
 int main(int argc, char **argv) {
+#ifdef __OpenBSD__
+	/* - rpath is required to read --extra-opts (given up later)
+	 * - inet is required for sockets
+	 * - unix is required for Unix domain sockets
+	 * - dns is required for name lookups */
+	pledge("stdio rpath inet unix dns", NULL);
+#endif // __OpenBSD__
+
 	setlocale(LC_ALL, "");
 	bindtextdomain(PACKAGE, LOCALEDIR);
 	textdomain(PACKAGE);
@@ -216,6 +224,10 @@ int main(int argc, char **argv) {
 		usage4(_("Could not parse arguments"));
 	}
 
+#ifdef __OpenBSD__
+	pledge("stdio inet unix dns", NULL);
+#endif // __OpenBSD__
+
 	config = paw.config;
 
 	if (verbosity > 0) {