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.

1 files changed, 17 insertions, 0 deletions

diff --git a/plugins/check_curl.c b/plugins/check_curl.c
index 1dec8a2a..19d36237 100644
--- a/plugins/check_curl.c
+++ b/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);
         }