Use pledge(2) and unveil(2) on OpenBSD

It has been on my todo-list for a long time. I tested it on
OpenBSD 6.5.

Thanks Richard Ulmer for the reminder.

Signed-off-by: Laslo Hunhold <dev@frign.de>

main.c

@@ -325,6 +325,10 @@ main(int argc, char *argv[])
 			die("signal: Failed to set SIG_IGN on SIGCHLD");
 		}
 
+		/* limit ourselves to reading the servedir and block further unveils */
+		eunveil(servedir, "r");
+		eunveil(NULL, NULL);
+
 		/* chroot */
 		if (chdir(servedir) < 0) {
 			die("chdir '%s':", servedir);
@@ -343,6 +347,13 @@ main(int argc, char *argv[])
 		if (pwd && setuid(pwd->pw_uid) < 0) {
 			die("setuid:");
 		}
+
+		if (udsname) {
+			epledge("stdio rpath proc unix", NULL);
+		} else {
+			epledge("stdio rpath proc inet", NULL);
+		}
+
 		if (getuid() == 0) {
 			die("Won't run as root user", argv0);
 		}
@@ -375,6 +386,14 @@ main(int argc, char *argv[])
 		}
 		exit(0);
 	default:
+		/* limit ourselves even further while we are waiting */
+		eunveil(NULL, NULL);
+		if (udsname) {
+			epledge("stdio cpath", NULL);
+		} else {
+			epledge("stdio", NULL);
+		}
+
 		while ((wpid = wait(&status)) > 0)
 			;
 	}

util.c

@@ -9,6 +9,10 @@
 #include <sys/types.h>
 #include <time.h>
 
+#ifdef __OpenBSD__
+#include <unistd.h>
+#endif /* __OpenBSD__ */
+
 #include "util.h"
 
 char *argv0;
@@ -53,6 +57,32 @@ die(const char *fmt, ...)
 	exit(1);
 }
 
+void
+epledge(const char *promises, const char *execpromises)
+{
+	(void)promises;
+	(void)execpromises;
+
+#ifdef __OpenBSD__
+	if (pledge(promises, execpromises) == -1) {
+		die("pledge:");
+	}
+#endif /* __OpenBSD__ */
+}
+
+void
+eunveil(const char *path, const char *permissions)
+{
+	(void)path;
+	(void)permissions;
+
+#ifdef __OpenBSD__
+	if (unveil(path, permissions) == -1) {
+		die("unveil:");
+	}
+#endif /* __OpenBSD__ */
+}
+
 char *
 timestamp(time_t t, char buf[TIMESTAMP_LEN])
 {

util.h

@@ -46,6 +46,9 @@ extern char *argv0;
 void warn(const char *, ...);
 void die(const char *, ...);
 
+void epledge(const char *, const char *);
+void eunveil(const char *, const char *);
+
 #define TIMESTAMP_LEN 30
 
 char *timestamp(time_t, char buf[TIMESTAMP_LEN]);