[tor-commits] [tor/maint-0.4.4] statistics: Properly count all rendezvous cells (avoid undercounting).

[dgoulet at torproject.org]

commit 85a1e6c6018153f76afe175e51e0199dd2651678
Author: George Kadianakis <desnacked at riseup.net>
Date:   Mon Sep 7 13:17:41 2020 +0300

    statistics: Properly count all rendezvous cells (avoid undercounting).
    
    tl;dr We were not counting cells flying from the client to the service, but we
    were counting cells flying from the service to the client.
    
    When a rendezvous cell arrives from the client to the RP, the RP forwards it to
    the service.
    
    For this to happen, the cell first passes through command_process_relay_cell()
    which normally does the statistics counting. However because the `rend_circ`
    circuit was not flagged with `circuit_carries_hs_traffic_stats` in
    rend_mid_rendezvous(), the cell is not counted there.
    
    Then the cell goes to circuit_receive_relay_cell() which has a special code
    block based on `rend_splice` specifically for rendezvous cells, and the cell
    gets directly passed to `rend_circ` via a direct call to
    circuit_receive_relay_cell(). The cell never passes through
    command_process_relay_cell() ever again and hence is never counted by our
    rephist module.
    
    The fix here is to flag the `rend_circ` circuit with
    `circuit_carries_hs_traffic_stats` so that the cell is counted as soon as it
    hits command_process_relay_cell().
    
    Furthermore we avoid double-counting cells since the special code block of
    circuit_receive_relay_cell() makes us count rendezvous cells only as they enter
    the RP and not as they exit it.
    
    Fixes #40117.
---
 changes/bug40117           | 5 +++++
 src/feature/rend/rendmid.c | 6 ++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/changes/bug40117 b/changes/bug40117
new file mode 100644
index 0000000000..77646edf9c
--- /dev/null
+++ b/changes/bug40117
@@ -0,0 +1,5 @@
+  o Major bugfixes (stats, onion services):
+    - Fix a bug where we were undercounting the Tor network's total onion
+      service traffic, by only counting rendezvous traffic originating from
+      services and ignoring any traffic originating from clients. Fixes bug
+      40117; bugfix on 0.2.6.2-alpha.
diff --git a/src/feature/rend/rendmid.c b/src/feature/rend/rendmid.c
index a473f0c7e1..b497362857 100644
--- a/src/feature/rend/rendmid.c
+++ b/src/feature/rend/rendmid.c
@@ -343,10 +343,12 @@ rend_mid_rendezvous(or_circuit_t *circ, const uint8_t *request,
     goto err;
   }
 
-  /* Statistics: Mark this circuit as an RP circuit so that we collect
-     stats from it. */
+  /* Statistics: Mark circuits as RP circuits */
   if (options->HiddenServiceStatistics) {
+    /* `circ` is the RP <-> service circuit */
     circ->circuit_carries_hs_traffic_stats = 1;
+    /* `rend_circ` is the client <-> RP circuit */
+    rend_circ->circuit_carries_hs_traffic_stats = 1;
   }
 
   /* Send the RENDEZVOUS2 cell to the client. */