Don't let bad DNS make exit policy and declared exit policy get out of sync

Patch from "postman" on trac. Fixes bg 2366. Bug on 0.1.2.5-alpha.

changes/bug2366

@@ -0,0 +1,8 @@
+  o Minor bugfixes
+    - When a relay decides that its DNS is too broken for it to serve
+      as an exit server, it advertised itself as a non-exit, but
+      continued to act as an exit.  This could create accidental
+      partitioning opportunities for users.  Instead, if a relay is
+      going to advertise reject *:* as its exit policy, it should
+      really act with exit policy "reject *:*". Fixes bug 2366.
+      Bugfix on Tor 0.1.2.5-alpha.  Bugfix by user "postman" on trac.

src/or/policies.c

@@ -858,6 +858,14 @@ policies_parse_exit_policy(config_line_t *cfg, smartlist_t **dest,
   return 0;
 }
 
+/** Add "reject *:*" to the end of the policy in *<b>dest</b>, allocating
+ * *<b>dest</b> as needed. */
+void
+policies_exit_policy_append_reject_star(smartlist_t **dest)
+{
+  append_exit_policy_string(dest, "reject *:*");
+}
+
 /** Replace the exit policy of <b>r</b> with reject *:*. */
 void
 policies_set_router_exitpolicy_to_reject_all(routerinfo_t *r)

src/or/policies.h

@@ -41,6 +41,7 @@ addr_policy_result_t compare_addr_to_addr_policy(uint32_t addr,
 int policies_parse_exit_policy(config_line_t *cfg, smartlist_t **dest,
                                int rejectprivate, const char *local_address,
                                int add_default_policy);
+void policies_exit_policy_append_reject_star(smartlist_t **dest);
 void policies_set_router_exitpolicy_to_reject_all(routerinfo_t *exitrouter);
 int exit_policy_is_general_exit(smartlist_t *policy);
 int policy_is_reject_star(const smartlist_t *policy);

src/or/router.c

@@ -1410,9 +1410,14 @@ router_rebuild_descriptor(int force)
 
   ri->bandwidthcapacity = hibernating ? 0 : rep_hist_bandwidth_assess();
 
-  policies_parse_exit_policy(options->ExitPolicy, &ri->exit_policy,
-                             options->ExitPolicyRejectPrivate,
-                             ri->address, !options->BridgeRelay);
+  if (dns_seems_to_be_broken() || has_dns_init_failed()) {
+    /* DNS is screwed up; don't claim to be an exit. */
+    policies_exit_policy_append_reject_star(&ri->exit_policy);
+  } else {
+    policies_parse_exit_policy(options->ExitPolicy, &ri->exit_policy,
+                               options->ExitPolicyRejectPrivate,
+                               ri->address, !options->BridgeRelay);
+  }
   ri->policy_is_reject_star =
     policy_is_reject_star(ri->exit_policy);
 
@@ -1866,9 +1871,7 @@ router_dump_router_to_string(char *s, size_t maxlen, routerinfo_t *router,
   }
 
   /* Write the exit policy to the end of 's'. */
-  if (dns_seems_to_be_broken() || has_dns_init_failed() ||
-      !router->exit_policy || !smartlist_len(router->exit_policy)) {
-    /* DNS is screwed up; don't claim to be an exit. */
+  if (!router->exit_policy || !smartlist_len(router->exit_policy)) {
     strlcat(s+written, "reject *:*\n", maxlen-written);
     written += strlen("reject *:*\n");
     tmpe = NULL;