Netflow record collapsing defense.

This defense will cause Cisco, Juniper, Fortinet, and other routers operating
in the default configuration to collapse netflow records that would normally
be split due to the 15 second flow idle timeout.

Collapsing these records should greatly reduce the utility of default netflow
data for correlation attacks, since all client-side records should become 30
minute chunks of total bytes sent/received, rather than creating multiple
separate records for every webpage load/ssh command interaction/XMPP chat/whatever
else happens to be inactive for more than 15 seconds.

The defense adds consensus parameters to govern the range of timeout values
for sending padding packets, as well as for keeping connections open.

The defense only sends padding when connections are otherwise inactive, and it
does not pad connections used solely for directory traffic at all. By default
it also doesn't pad inter-relay connections.

Statistics on the total padding in the last 24 hours are exported to the
extra-info descriptors.

1 files changed, 40 insertions, 2 deletions

diff --git a/src/or/channel.c b/src/or/channel.c
index a1ccb2c8e3..74793436da 100644
--- a/src/or/channel.c
+++ b/src/or/channel.c
@@ -49,6 +49,7 @@
 #include "or.h"
 #include "channel.h"
 #include "channeltls.h"
+#include "channelpadding.h"
 #include "circuitbuild.h"
 #include "circuitlist.h"
 #include "circuitstats.h"
@@ -63,6 +64,7 @@
 #include "router.h"
 #include "routerlist.h"
 #include "scheduler.h"
+#include "compat_time.h"
 
 /* Global lists of channels */
 
@@ -105,6 +107,8 @@ HT_GENERATE2(channel_gid_map, channel_s, gidmap_node,
              channel_id_hash, channel_id_eq,
              0.6, tor_reallocarray_, tor_free_);
 
+HANDLE_IMPL(channel, channel_s,);
+
 /* Counter for ID numbers */
 static uint64_t n_channels_allocated = 0;
 /*
@@ -922,6 +926,11 @@ channel_free(channel_t *chan)
     circuitmux_set_policy(chan->cmux, NULL);
   }
 
+  /* Remove all timers and associated handle entries now */
+  timer_free(chan->padding_timer);
+  channel_handle_free(chan->timer_handle);
+  channel_handles_clear(chan);
+
   /* Call a free method if there is one */
   if (chan->free_fn) chan->free_fn(chan);
 
@@ -1000,6 +1009,11 @@ channel_force_free(channel_t *chan)
     circuitmux_set_policy(chan->cmux, NULL);
   }
 
+  /* Remove all timers and associated handle entries now */
+  timer_free(chan->padding_timer);
+  channel_handle_free(chan->timer_handle);
+  channel_handles_clear(chan);
+
   /* Call a free method if there is one */
   if (chan->free_fn) chan->free_fn(chan);
 
@@ -2619,6 +2633,19 @@ channel_do_open_actions(channel_t *chan)
     }
   }
 
+  /* Disable or reduce padding according to user prefs. */
+  if (chan->padding_enabled || get_options()->ConnectionPadding == 1) {
+    if (!get_options()->ConnectionPadding) {
+      channelpadding_disable_padding_on_channel(chan);
+    }
+
+    /* Padding can be forced and/or reduced by clients, regardless of if
+     * the channel supports it */
+    if (get_options()->ReducedConnectionPadding) {
+      channelpadding_reduce_padding_on_channel(chan);
+    }
+  }
+
   circuit_n_chan_done(chan, 1, close_origin_circuits);
 }
 
@@ -4215,8 +4242,12 @@ channel_timestamp_active(channel_t *chan)
   time_t now = time(NULL);
 
   tor_assert(chan);
+  chan->timestamp_xfer_ms = monotime_coarse_absolute_msec();
 
   chan->timestamp_active = now;
+
+  /* Clear any potential netflow padding timer. We're active */
+  chan->next_padding_time_ms = 0;
 }
 
 /**
@@ -4299,11 +4330,14 @@ void
 channel_timestamp_recv(channel_t *chan)
 {
   time_t now = time(NULL);
-
   tor_assert(chan);
+  chan->timestamp_xfer_ms = monotime_coarse_absolute_msec();
 
   chan->timestamp_active = now;
   chan->timestamp_recv = now;
+
+  /* Clear any potential netflow padding timer. We're active */
+  chan->next_padding_time_ms = 0;
 }
 
 /**
@@ -4316,11 +4350,15 @@ void
 channel_timestamp_xmit(channel_t *chan)
 {
   time_t now = time(NULL);
-
   tor_assert(chan);
 
+  chan->timestamp_xfer_ms = monotime_coarse_absolute_msec();
+
   chan->timestamp_active = now;
   chan->timestamp_xmit = now;
+
+  /* Clear any potential netflow padding timer. We're active */
+  chan->next_padding_time_ms = 0;
 }
 
 /***************************************************************