[tor-commits] [tor/release-0.4.3] Adjust the rules for warning about too many connections.

[nickm at torproject.org]

commit faa752f3c9bd3faa2d23e6273f657771a3cad078
Author: Nick Mathewson <nickm at torproject.org>
Date:   Wed Jul 22 14:45:03 2020 -0400

    Adjust the rules for warning about too many connections.
    
    Previously we tolerated up to 1.5 connections for every relay we
    were connected to, and didn't warn if we had fewer than 5
    connections total.
    
    Now we tolerate up to 1.5 connections per relay, and up to 4
    connections per authority, and we don't warn at all when we have
    fewer than 25 connections total.
    
    Fixes bug 33880, which seems to have been provoked by our #17592
    change in 0.3.5.
---
 changes/ticket33880   |  6 ++++++
 src/core/or/channel.c | 32 +++++++++++++++++++++++++++++---
 2 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/changes/ticket33880 b/changes/ticket33880
new file mode 100644
index 0000000000..c1889bb134
--- /dev/null
+++ b/changes/ticket33880
@@ -0,0 +1,6 @@
+  o Minor bugfixes (relay, usability):
+    - Adjust the rules for when to warn about having too many connections
+      to other relays. Previously we'd tolerate up to 1.5 connections
+      per relay on average.  Now we tolerate more connections for directory
+      authorities, and raise the number of total connections we need
+      to see before we warn.  Fixes bug 33880; bugfix on 0.3.1.1-alpha.
diff --git a/src/core/or/channel.c b/src/core/or/channel.c
index 3886906875..71cb6bccbb 100644
--- a/src/core/or/channel.c
+++ b/src/core/or/channel.c
@@ -72,6 +72,7 @@
 #include "core/or/relay.h"
 #include "core/or/scheduler.h"
 #include "feature/client/entrynodes.h"
+#include "feature/nodelist/dirlist.h"
 #include "feature/nodelist/networkstatus.h"
 #include "feature/nodelist/nodelist.h"
 #include "feature/nodelist/routerlist.h"
@@ -749,6 +750,7 @@ channel_check_for_duplicates(void)
 {
   channel_idmap_entry_t **iter;
   channel_t *chan;
+  int total_dirauth_connections = 0, total_dirauths = 0;
   int total_relay_connections = 0, total_relays = 0, total_canonical = 0;
   int total_half_canonical = 0;
   int total_gt_one_connection = 0, total_gt_two_connections = 0;
@@ -756,13 +758,18 @@ channel_check_for_duplicates(void)
 
   HT_FOREACH(iter, channel_idmap, &channel_identity_map) {
     int connections_to_relay = 0;
+    const char *id_digest = (char *) (*iter)->digest;
 
     /* Only consider relay connections */
-    if (!connection_or_digest_is_known_relay((char*)(*iter)->digest))
+    if (!connection_or_digest_is_known_relay(id_digest))
       continue;
 
     total_relays++;
 
+    const bool is_dirauth = router_digest_is_trusted_dir(id_digest);
+    if (is_dirauth)
+      total_dirauths++;
+
     for (chan = TOR_LIST_FIRST(&(*iter)->channel_list); chan;
         chan = channel_next_with_rsa_identity(chan)) {
 
@@ -771,6 +778,8 @@ channel_check_for_duplicates(void)
 
       connections_to_relay++;
       total_relay_connections++;
+      if (is_dirauth)
+        total_dirauth_connections++;
 
       if (chan->is_canonical(chan, 0)) total_canonical++;
 
@@ -785,11 +794,28 @@ channel_check_for_duplicates(void)
     if (connections_to_relay > 4) total_gt_four_connections++;
   }
 
-#define MIN_RELAY_CONNECTIONS_TO_WARN 5
+  /* Don't bother warning about excessive connections unless we have
+   * at least this many connections, total.
+   */
+#define MIN_RELAY_CONNECTIONS_TO_WARN 25
+  /* If the average number of connections for a regular relay is more than
+   * this, that's too high.
+   */
+#define MAX_AVG_RELAY_CONNECTIONS 1.5
+  /* If the average number of connections for a dirauth is more than
+   * this, that's too high.
+   */
+#define MAX_AVG_DIRAUTH_CONNECTIONS 4
+
+  /* How many connections total would be okay, given the number of
+   * relays and dirauths that we have connections to? */
+  const int max_tolerable_connections = (int)(
+    (total_relays-total_dirauths) * MAX_AVG_RELAY_CONNECTIONS +
+    total_dirauths * MAX_AVG_DIRAUTH_CONNECTIONS);
 
   /* If we average 1.5 or more connections per relay, something is wrong */
   if (total_relays > MIN_RELAY_CONNECTIONS_TO_WARN &&
-          total_relay_connections >= 1.5*total_relays) {
+      total_relay_connections > max_tolerable_connections) {
     log_notice(LD_OR,
         "Your relay has a very large number of connections to other relays. "
         "Is your outbound address the same as your relay address? "