From bbb75ff6eeda25e2f0eebd0a6639efd48b4dbb3c Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Date: Mon, 16 Dec 2019 13:14:37 +0000
Subject: [PATCH] Exclude rejected state events when calculating state at
backwards extrems (#6527)
This fixes a weird bug where, if you were determined enough, you could end up with a rejected event forming part of the state at a backwards-extremity. Authing that backwards extrem would then lead to us trying to pull the rejected event from the db (with allow_rejected=False), which would fail with a 404.
---
changelog.d/6527.bugfix | 1 +
synapse/handlers/federation.py | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)
create mode 100644 changelog.d/6527.bugfix
diff --git a/changelog.d/6527.bugfix b/changelog.d/6527.bugfix
new file mode 100644
index 0000000000..53214b0748
--- /dev/null
+++ b/changelog.d/6527.bugfix
@@ -0,0 +1 @@
+Fix a bug which could cause the federation server to incorrectly return errors when handling certain obscure event graphs.
\ No newline at end of file
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index f4ac0bfbc8..abe02907b9 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -606,7 +606,7 @@ class FederationHandler(BaseHandler):
remote_event = event_map.get(event_id)
if not remote_event:
raise Exception("Unable to get missing prev_event %s" % (event_id,))
- if remote_event.is_state():
+ if remote_event.is_state() and remote_event.rejected_reason is None:
remote_state.append(remote_event)
auth_chain = [event_map[e_id] for e_id in auth_event_ids if e_id in event_map]
--
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