drop privileges, FreeBSD.

Expand on sandboxing support, assuming memcached
does not support end of life versions (available
since FreeBSD 10.x ~2014).

freebsd_priv.c

@@ -11,6 +11,33 @@
  * in FreeBSD vocabulary.
  */
 void drop_privileges() {
+    cap_rights_t wd, rd;
+
+    if (cap_rights_init(&wd, CAP_WRITE, CAP_READ) == NULL) {
+        fprintf(stderr, "cap_rights_init write protection failed: %s\n", strerror(errno));
+        exit(EXIT_FAILURE);
+    }
+
+    if (cap_rights_init(&rd, CAP_FCNTL, CAP_READ, CAP_EVENT) == NULL) {
+        fprintf(stderr, "cap_rights_init read protection failed: %s\n", strerror(errno));
+        exit(EXIT_FAILURE);
+    }
+
+    if (cap_rights_limit(STDIN_FILENO, &rd) != 0) {
+        fprintf(stderr, "cap_rights_limit stdin failed: %s\n", strerror(errno));
+        exit(EXIT_FAILURE);
+    }
+
+    if (cap_rights_limit(STDOUT_FILENO, &wd) != 0) {
+        fprintf(stderr, "cap_rights_limit stdout failed: %s\n", strerror(errno));
+        exit(EXIT_FAILURE);
+    }
+
+    if (cap_rights_limit(STDERR_FILENO, &wd) != 0) {
+        fprintf(stderr, "cap_rights_limit stderr failed: %s\n", strerror(errno));
+        exit(EXIT_FAILURE);
+    }
+
     if (cap_enter() != 0) {
         fprintf(stderr, "cap_enter failed: %s\n", strerror(errno));
         exit(EXIT_FAILURE);