backport candidate:

If not enough of our entry guards are available so we add a new
one, we might use the new one even if it overlapped with the
current circuit's exit relay (or its family). Anonymity bugfix
pointed out by rovv.


svn:r16698

ChangeLog

-Changes in version 0.2.1.5-alpha - 2008-08-??
+Changes in version 0.2.1.5-alpha - 2008-09-??
   o Major features [IPv6 support]:
     - Convert many internal address representations to optionally hold
       IPv6 addresses.
@@ -18,6 +18,10 @@ Changes in version 0.2.1.5-alpha - 2008-08-??
       a digest of all zeroes, or asks to extend back to the relay that
       sent the extend cell, tear down the circuit. Ideas suggested
       by rovv.
+    - If not enough of our entry guards are available so we add a new
+      one, we might use the new one even if it overlapped with the
+      current circuit's exit relay (or its family). Anonymity bugfix
+      pointed out by rovv.
 
   o Minor bugfixes:
     - Recover 3-7 bytes that were wasted per memory chunk.  Fixes bug

src/or/circuitbuild.c

@@ -2476,8 +2476,13 @@ choose_random_entry(cpath_build_state_t *state)
        * be a long time til we get it. -RD */
       r = add_an_entry_guard(NULL, 0);
       if (r) {
-        smartlist_add(live_entry_guards, r);
         entry_guards_changed();
+        /* XXX we start over here in case the new node we added shares
+         * a family with our exit node. There's a chance that we'll just
+         * load up on entry guards here, if the network we're using is
+         * one big family. Perhaps we should teach add_an_entry_guard()
+         * to understand nodes-to-avoid-if-possible? -RD */
+        goto retry;
       }
     }
     if (!r && need_uptime) {