Warn if Tor is a relay and a HS

Closes 12908; see #8742

changes/bug12908

@@ -0,0 +1,4 @@
+  o Minor features:
+    - Warn about attempts to run hidden services and relays in the
+      same process: that's probably not a good idea. Closes ticket
+      12908.

src/or/config.c

@@ -2563,6 +2563,13 @@ options_validate(or_options_t *old_options, or_options_t *options,
     REJECT("Can't use a relative path to torrc when RunAsDaemon is set.");
 #endif
 
+  if (server_mode(options) && options->RendConfigLines)
+    log_warn(LD_CONFIG,
+        "Tor is currently configured as a relay and a hidden service. "
+        "That's not very secure: you should probably run your hidden service "
+        "in a separate Tor process, at least -- see "
+        "https://trac.torproject.org/8742");
+
   /* XXXX require that the only port not be DirPort? */
   /* XXXX require that at least one port be listened-upon. */
   if (n_ports == 0 && !options->RendConfigLines)