[tor-commits] [tor/master] document a cool attack that we evaluated

[arma at torproject.org]

commit 3a94530595cfb57bdb4e3401d29a8a4d0b638d01
Author: Roger Dingledine <arma at torproject.org>
Date:   Fri Feb 17 14:02:25 2012 -0500

    document a cool attack that we evaluated
---
 src/or/policies.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/src/or/policies.c b/src/or/policies.c
index 0982b4b..e5062cd 100644
--- a/src/or/policies.c
+++ b/src/or/policies.c
@@ -1452,7 +1452,17 @@ compare_tor_addr_to_short_policy(const tor_addr_t *addr, uint16_t port,
   else
     accept = ! policy->is_accept;
 
-  /* ???? are these right? */
+  /* ???? are these right? -NM */
+  /* We should be sure not to return ADDR_POLICY_ACCEPTED in the accept
+   * case here, because it would cause clients to believe that the node
+   * allows exit enclaving. Trying it anyway would open up a cool attack
+   * where the node refuses due to exitpolicy, the client reacts in
+   * surprise by rewriting the node's exitpolicy to reject *:*, and then
+   * a bad guy targets users by causing them to attempt such connections
+   * to 98% of the exits.
+   *
+   * Once microdescriptors can handle addresses in special cases (e.g. if
+   * we ever solve ticket 1774), we can provide certainty here. -RD */
   if (accept)
     return ADDR_POLICY_PROBABLY_ACCEPTED;
   else