[tor-commits] [tor/maint-0.4.3] dirauth: Resume sending 503 directory error code

[nickm at torproject.org]

commit 6d9113d2f65b6e3142efdaa91a5b4761cd197be8
Author: David Goulet <dgoulet at torproject.org>
Date:   Tue Jan 28 09:39:09 2020 -0500

    dirauth: Resume sending 503 directory error code
    
    Authorities were never sending back 503 error code because by design they
    should be able to always answer directory requests regardless of bandwidth
    capacity.
    
    However, that recently backfired because of a large number of requests from
    unknown source using the DirPort that are _not_ getting their 503 code which
    overloaded the DirPort leading to the authority to be unable to answer to its
    fellow authorities.
    
    This is not a complete solution to the problem but it will help ease off the
    load on the authority side by sending back 503 codes *unless* the connection
    is from a known relay or an authority.
    
    Fixes #33029
    
    Signed-off-by: David Goulet <dgoulet at torproject.org>
---
 changes/ticket33029            |  5 +++++
 src/core/mainloop/connection.c | 17 +++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/changes/ticket33029 b/changes/ticket33029
new file mode 100644
index 000000000..c32ee4ad8
--- /dev/null
+++ b/changes/ticket33029
@@ -0,0 +1,5 @@
+  o Major bugfixes (directory authority):
+    - Directory authorities will now send a 503 (not enough bandwidth) code to
+      clients when under bandwidth pressure. Known relays and other authorities
+      will always be answered regardless of the bandwidth situation. Fixes bug
+      33029; bugfix on 0.1.2.5-alpha.
diff --git a/src/core/mainloop/connection.c b/src/core/mainloop/connection.c
index a157c0f3f..50cd3810a 100644
--- a/src/core/mainloop/connection.c
+++ b/src/core/mainloop/connection.c
@@ -3211,8 +3211,21 @@ connection_dir_is_global_write_low(const connection_t *conn, size_t attempt)
   size_t smaller_bucket =
     MIN(token_bucket_rw_get_write(&global_bucket),
         token_bucket_rw_get_write(&global_relayed_bucket));
-  if (authdir_mode(get_options()))
-    return false; /* there's always room to answer v2 if we're an auth dir */
+
+  /* Special case for authorities (directory only). */
+  if (authdir_mode_v3(get_options())) {
+    /* Are we configured to possibly reject requests under load? */
+    if (!get_options()->AuthDirRejectRequestsUnderLoad) {
+      /* Answer request no matter what. */
+      return false;
+    }
+    /* Always answer requests from a known relay which includes the other
+     * authorities. The following looks up the addresses for relays that we
+     * have their descriptor _and_ any configured trusted directories. */
+    if (nodelist_probably_contains_address(&conn->addr)) {
+      return false;
+    }
+  }
 
   if (!connection_is_rate_limited(conn))
     return false; /* local conns don't get limited */