feat: add option to ignore specific server signing keys

docs/configuration.md

@@ -57,6 +57,7 @@ The `global` section contains the following fields:
 | `turn_uris` | `array` | The TURN URIs | `[]` |
 | `turn_secret` | `string` | The TURN secret | `""` |
 | `turn_ttl` | `integer` | The TURN TTL in seconds | `86400` |
+| `ignored_keys` | `[string]` | Server keys that should be ignored | `["l/O9hxMVKB6Lg+3Hqf0FQQZhVESQcMzbPN1Cz2nM3og"]` ([ESS compromised key](https://github.com/element-hq/ess-helm/security/advisories/GHSA-qwcj-h6m8-vp6q)) |
 | `media` | `table` | See the [media configuration](#media) | See the [media configuration](#media) |
 | `emergency_password` | `string` | Set a password to login as the `conduit` user in case of emergency | N/A |
 | `well_known` | `table` | Used for [delegation](delegation.md) | See [delegation](delegation.md) |

src/config/mod.rs

@@ -8,7 +8,7 @@ use std::{
 };
 
 use bytesize::ByteSize;
-use ruma::{OwnedServerName, RoomVersionId};
+use ruma::{api::federation::discovery::VerifyKey, serde::Base64, OwnedServerName, RoomVersionId};
 use serde::{de::IgnoredAny, Deserialize};
 use tokio::time::{interval, Interval};
 use tracing::warn;
@@ -89,6 +89,9 @@ pub struct IncompleteConfig {
 
     pub turn: Option<TurnConfig>,
 
+    #[serde(default = "default_ignored_keys")]
+    pub ignored_keys: Vec<VerifyKey>,
+
     #[serde(default)]
     pub media: IncompleteMediaConfig,
 
@@ -136,6 +139,8 @@ pub struct Config {
 
     pub turn: Option<TurnConfig>,
 
+    pub ignored_keys: Vec<Base64>,
+
     pub media: MediaConfig,
 
     pub emergency_password: Option<String>,
@@ -186,6 +191,7 @@ impl From<IncompleteConfig> for Config {
             media,
             emergency_password,
             catchall,
+            ignored_keys,
         } = val;
 
         let turn = turn.or_else(|| {
@@ -204,6 +210,8 @@ impl From<IncompleteConfig> for Config {
             }
         });
 
+        let ignored_keys = ignored_keys.into_iter().map(|key| key.key).collect();
+
         let well_known_client = well_known
             .client
             .map(String::from)
@@ -283,6 +291,7 @@ impl From<IncompleteConfig> for Config {
             media,
             emergency_password,
             catchall,
+            ignored_keys,
         }
     }
 }
@@ -786,3 +795,12 @@ pub fn default_default_room_version() -> RoomVersionId {
 fn default_s3_duration() -> u64 {
     30
 }
+
+fn default_ignored_keys() -> Vec<VerifyKey> {
+    vec![VerifyKey::new(Base64::new(
+        // Compromised Element Server Suite (ESS) signing key:
+        //
+        // https://github.com/element-hq/ess-helm/security/advisories/GHSA-qwcj-h6m8-vp6q
+        b"l/O9hxMVKB6Lg+3Hqf0FQQZhVESQcMzbPN1Cz2nM3og".to_vec(),
+    ))]
+}

src/service/globals/mod.rs

@@ -421,7 +421,7 @@ impl Service {
     }
 
     /// Filters the key map of multiple servers down to keys that should be accepted given the expiry time,
-    /// room version, and timestamp of the parameters
+    /// room version, and timestamp of the parameters, as well as ignoring keys that are listed in `ignored_keys`.
     pub fn filter_keys_server_map(
         &self,
         keys: BTreeMap<String, SigningKeys>,
@@ -437,7 +437,7 @@ impl Service {
     }
 
     /// Filters the keys of a single server down to keys that should be accepted given the expiry time,
-    /// room version, and timestamp of the parameters
+    /// room version, and timestamp of the parameters, as well as removing any keys in `ignored_keys`.
     pub fn filter_keys_single_server(
         &self,
         keys: SigningKeys,
@@ -449,22 +449,32 @@ impl Service {
             // https://spec.matrix.org/v1.10/server-server-api/#get_matrixkeyv2server
                 || !rules.enforce_key_validity
         {
+            let filter_ignored_keys = |(_, base64): &(_, Base64)| {
+                !services().globals.config.ignored_keys.contains(base64)
+            };
+
             // Given that either the room version allows stale keys, or the valid_until_ts is
             // in the future, all verify_keys are valid
             let mut map: BTreeMap<_, _> = keys
                 .verify_keys
                 .into_iter()
                 .map(|(id, key)| (id, key.key))
+                .filter(filter_ignored_keys)
                 .collect();
 
-            map.extend(keys.old_verify_keys.into_iter().filter_map(|(id, key)| {
-                // Even on old room versions, we don't allow old keys if they are expired
-                if key.expired_ts > timestamp {
-                    Some((id, key.key))
-                } else {
-                    None
-                }
-            }));
+            map.extend(
+                keys.old_verify_keys
+                    .into_iter()
+                    .filter_map(|(id, key)| {
+                        // Even on old room versions, we don't allow old keys if they are expired
+                        if key.expired_ts > timestamp {
+                            Some((id, key.key))
+                        } else {
+                            None
+                        }
+                    })
+                    .filter(filter_ignored_keys),
+            );
 
             Some(map)
         } else {

src/service/rooms/event_handler/mod.rs

@@ -1421,7 +1421,8 @@ impl Service {
         Ok((sorted, eventid_info))
     }
 
-    /// Filters down the given signing keys, only keeping those which could be valid for this event.
+    /// Filters down the given signing keys, only keeping those which could be valid for this event,
+    /// as well as ignoring those listed in `ignored_keys`.
     #[tracing::instrument(skip_all)]
     pub async fn filter_required_signing_keys(
         &self,