matrix-synapse vulnerable to denial of service due to malicious server ACL events

@@ -0,0 +1 @@
+Cache server ACL checking.

@@ -0,0 +1,102 @@
+// Copyright 2023 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! An implementation of Matrix server ACL rules.
+
+use std::net::Ipv4Addr;
+use std::str::FromStr;
+
+use anyhow::Error;
+use pyo3::prelude::*;
+use regex::Regex;
+
+use crate::push::utils::{glob_to_regex, GlobMatchType};
+
+/// Called when registering modules with python.
+pub fn register_module(py: Python<'_>, m: &PyModule) -> PyResult<()> {
+    let child_module = PyModule::new(py, "acl")?;
+    child_module.add_class::<ServerAclEvaluator>()?;
+
+    m.add_submodule(child_module)?;
+
+    // We need to manually add the module to sys.modules to make `from
+    // synapse.synapse_rust import acl` work.
+    py.import("sys")?
+        .getattr("modules")?
+        .set_item("synapse.synapse_rust.acl", child_module)?;
+
+    Ok(())
+}
+
+#[derive(Debug, Clone)]
+#[pyclass(frozen)]
+pub struct ServerAclEvaluator {
+    allow_ip_literals: bool,
+    allow: Vec<Regex>,
+    deny: Vec<Regex>,
+}
+
+#[pymethods]
+impl ServerAclEvaluator {
+    #[new]
+    pub fn py_new(
+        allow_ip_literals: bool,
+        allow: Vec<&str>,
+        deny: Vec<&str>,
+    ) -> Result<Self, Error> {
+        let allow = allow
+            .iter()
+            .map(|s| glob_to_regex(s, GlobMatchType::Whole))
+            .collect::<Result<_, _>>()?;
+        let deny = deny
+            .iter()
+            .map(|s| glob_to_regex(s, GlobMatchType::Whole))
+            .collect::<Result<_, _>>()?;
+
+        Ok(ServerAclEvaluator {
+            allow_ip_literals,
+            allow,
+            deny,
+        })
+    }
+
+    pub fn server_matches_acl_event(&self, server_name: &str) -> bool {
+        // first of all, check if literal IPs are blocked, and if so, whether the
+        // server name is a literal IP
+        if !self.allow_ip_literals {
+            // check for ipv6 literals. These start with '['.
+            if server_name.starts_with('[') {
+                return false;
+            }
+
+            // check for ipv4 literals. We can just lift the routine from std::net.
+            if Ipv4Addr::from_str(server_name).is_ok() {
+                return false;
+            }
+        }
+
+        // next, check the deny list
+        if self.deny.iter().any(|e| e.is_match(server_name)) {
+            return false;
+        }
+
+        // then the allow list.
+        if self.allow.iter().any(|e| e.is_match(server_name)) {
+            return true;
+        }
+
+        // everything else should be rejected.
+        false
+    }
+}

@@ -2,6 +2,7 @@ use lazy_static::lazy_static;
 use pyo3::prelude::*;
 use pyo3_log::ResetHandle;
 
+pub mod acl;
 pub mod push;
 
 lazy_static! {
@@ -38,6 +39,7 @@ fn synapse_rust(py: Python<'_>, m: &PyModule) -> PyResult<()> {
     m.add_function(wrap_pyfunction!(get_rust_file_digest, m)?)?;
     m.add_function(wrap_pyfunction!(reset_logging_config, m)?)?;
 
+    acl::register_module(py, m)?;
     push::register_module(py, m)?;
 
     Ok(())

@@ -0,0 +1,21 @@
+# Copyright 2023 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from typing import List
+
+class ServerAclEvaluator:
+    def __init__(
+        self, allow_ip_literals: bool, allow: List[str], deny: List[str]
+    ) -> None: ...
+    def server_matches_acl_event(self, server_name: str) -> bool: ...

@@ -39,9 +39,9 @@
     CANONICALJSON_MIN_INT,
     validate_canonicaljson,
 )
-from synapse.federation.federation_server import server_matches_acl_event
 from synapse.http.servlet import validate_json_object
 from synapse.rest.models import RequestBodyModel
+from synapse.storage.controllers.state import server_acl_evaluator_from_event
 from synapse.types import EventID, JsonDict, RoomID, StrCollection, UserID
 
 
@@ -106,7 +106,10 @@ def validate_new(self, event: EventBase, config: HomeServerConfig) -> None:
             self._validate_retention(event)
 
         elif event.type == EventTypes.ServerACL:
-            if not server_matches_acl_event(config.server.server_name, event):
+            server_acl_evaluator = server_acl_evaluator_from_event(event)
+            if not server_acl_evaluator.server_matches_acl_event(
+                config.server.server_name
+            ):
                 raise SynapseError(
                     400, "Can't create an ACL event that denies the local server"
                 )

@@ -29,10 +29,8 @@
     Union,
 )
 
-from matrix_common.regex import glob_to_regex
 from prometheus_client import Counter, Gauge, Histogram
 
-from twisted.internet.abstract import isIPAddress
 from twisted.python import failure
 
 from synapse.api.constants import (
@@ -1324,75 +1322,13 @@ async def check_server_matches_acl(self, server_name: str, room_id: str) -> None
         Raises:
             AuthError if the server does not match the ACL
         """
-        acl_event = await self._storage_controllers.state.get_current_state_event(
-            room_id, EventTypes.ServerACL, ""
+        server_acl_evaluator = (
+            await self._storage_controllers.state.get_server_acl_for_room(room_id)
         )
-        if not acl_event or server_matches_acl_event(server_name, acl_event):
-            return
-
-        raise AuthError(code=403, msg="Server is banned from room")
-
-
-def server_matches_acl_event(server_name: str, acl_event: EventBase) -> bool:
-    """Check if the given server is allowed by the ACL event
-
-    Args:
-        server_name: name of server, without any port part
-        acl_event: m.room.server_acl event
-
-    Returns:
-        True if this server is allowed by the ACLs
-    """
-    logger.debug("Checking %s against acl %s", server_name, acl_event.content)
-
-    # first of all, check if literal IPs are blocked, and if so, whether the
-    # server name is a literal IP
-    allow_ip_literals = acl_event.content.get("allow_ip_literals", True)
-    if not isinstance(allow_ip_literals, bool):
-        logger.warning("Ignoring non-bool allow_ip_literals flag")
-        allow_ip_literals = True
-    if not allow_ip_literals:
-        # check for ipv6 literals. These start with '['.
-        if server_name[0] == "[":
-            return False
-
-        # check for ipv4 literals. We can just lift the routine from twisted.
-        if isIPAddress(server_name):
-            return False
-
-    # next,  check the deny list
-    deny = acl_event.content.get("deny", [])
-    if not isinstance(deny, (list, tuple)):
-        logger.warning("Ignoring non-list deny ACL %s", deny)
-        deny = []
-    for e in deny:
-        if _acl_entry_matches(server_name, e):
-            # logger.info("%s matched deny rule %s", server_name, e)
-            return False
-
-    # then the allow list.
-    allow = acl_event.content.get("allow", [])
-    if not isinstance(allow, (list, tuple)):
-        logger.warning("Ignoring non-list allow ACL %s", allow)
-        allow = []
-    for e in allow:
-        if _acl_entry_matches(server_name, e):
-            # logger.info("%s matched allow rule %s", server_name, e)
-            return True
-
-    # everything else should be rejected.
-    # logger.info("%s fell through", server_name)
-    return False
-
-
-def _acl_entry_matches(server_name: str, acl_entry: Any) -> bool:
-    if not isinstance(acl_entry, str):
-        logger.warning(
-            "Ignoring non-str ACL entry '%s' (is %s)", acl_entry, type(acl_entry)
-        )
-        return False
-    regex = glob_to_regex(acl_entry)
-    return bool(regex.match(server_name))
+        if server_acl_evaluator and not server_acl_evaluator.server_matches_acl_event(
+            server_name
+        ):
+            raise AuthError(code=403, msg="Server is banned from room")
 
 
 class FederationHandlerRegistry:

@@ -2342,6 +2342,12 @@ async def _notify_persisted_event(
             # TODO retrieve the previous state, and exclude join -> join transitions
             self._notifier.notify_user_joined_room(event.event_id, event.room_id)
 
+        # If this is a server ACL event, clear the cache in the storage controller.
+        if event.type == EventTypes.ServerACL:
+            self._state_storage_controller.get_server_acl_for_room.invalidate(
+                (event.room_id,)
+            )
+
     def _sanity_check_event(self, ev: EventBase) -> None:
         """
         Do some early sanity checks of a received event

@@ -1730,6 +1730,11 @@ async def persist_and_notify_client_events(
                         event.event_id, event.room_id
                     )
 
+            if event.type == EventTypes.ServerACL:
+                self._storage_controllers.state.get_server_acl_for_room.invalidate(
+                    (event.room_id,)
+                )
+
             await self._maybe_kick_guest_users(event, context)
 
             if event.type == EventTypes.CanonicalAlias:

@@ -205,6 +205,12 @@ async def on_rdata(
                     self.notifier.notify_user_joined_room(
                         row.data.event_id, row.data.room_id
                     )
+
+                # If this is a server ACL event, clear the cache in the storage controller.
+                if row.data.type == EventTypes.ServerACL:
+                    self._state_storage_controller.get_server_acl_for_room.invalidate(
+                        (row.data.room_id,)
+                    )
         elif stream_name == UnPartialStatedRoomStream.NAME:
             for row in rows:
                 assert isinstance(row, UnPartialStatedRoomStreamRow)

@@ -37,6 +37,7 @@
     PartialCurrentStateTracker,
     PartialStateEventsTracker,
 )
+from synapse.synapse_rust.acl import ServerAclEvaluator
 from synapse.types import MutableStateMap, StateMap, get_domain_from_id
 from synapse.types.state import StateFilter
 from synapse.util.async_helpers import Linearizer
@@ -501,6 +502,31 @@ async def get_canonical_alias_for_room(self, room_id: str) -> Optional[str]:
 
         return event.content.get("alias")
 
+    @cached()
+    async def get_server_acl_for_room(
+        self, room_id: str
+    ) -> Optional[ServerAclEvaluator]:
+        """Get the server ACL evaluator for room, if any
+
+        This does up-front parsing of the content to ignore bad data and pre-compile
+        regular expressions.
+
+        Args:
+            room_id: The room ID
+
+        Returns:
+            The server ACL evaluator, if any
+        """
+
+        acl_event = await self.get_current_state_event(
+            room_id, EventTypes.ServerACL, ""
+        )
+
+        if not acl_event:
+            return None
+
+        return server_acl_evaluator_from_event(acl_event)
+
     @trace
     @tag_args
     async def get_current_state_deltas(
@@ -760,3 +786,36 @@ async def _get_joined_hosts(
                 cache.state_group = object()
 
         return frozenset(cache.hosts_to_joined_users)
+
+
+def server_acl_evaluator_from_event(acl_event: EventBase) -> "ServerAclEvaluator":
+    """
+    Create a ServerAclEvaluator from a m.room.server_acl event's content.
+
+    This does up-front parsing of the content to ignore bad data. It then creates
+    the ServerAclEvaluator which will pre-compile regular expressions from the globs.
+    """
+
+    # first of all, parse if literal IPs are blocked.
+    allow_ip_literals = acl_event.content.get("allow_ip_literals", True)
+    if not isinstance(allow_ip_literals, bool):
+        logger.warning("Ignoring non-bool allow_ip_literals flag")
+        allow_ip_literals = True
+
+    # next, parse the deny list by ignoring any non-strings.
+    deny = acl_event.content.get("deny", [])
+    if not isinstance(deny, (list, tuple)):
+        logger.warning("Ignoring non-list deny ACL %s", deny)
+        deny = []
+    else:
+        deny = [s for s in deny if isinstance(s, str)]
+
+    # then the allow list.
+    allow = acl_event.content.get("allow", [])
+    if not isinstance(allow, (list, tuple)):
+        logger.warning("Ignoring non-list allow ACL %s", allow)
+        allow = []
+    else:
+        allow = [s for s in allow if isinstance(s, str)]
+
+    return ServerAclEvaluator(allow_ip_literals, allow, deny)

@@ -22,10 +22,10 @@
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.config.server import DEFAULT_ROOM_VERSION
 from synapse.events import EventBase, make_event_from_dict
-from synapse.federation.federation_server import server_matches_acl_event
 from synapse.rest import admin
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
+from synapse.storage.controllers.state import server_acl_evaluator_from_event
 from synapse.types import JsonDict
 from synapse.util import Clock
 
@@ -67,37 +67,46 @@ def test_blocked_server(self) -> None:
         e = _create_acl_event({"allow": ["*"], "deny": ["evil.com"]})
         logging.info("ACL event: %s", e.content)
 
-        self.assertFalse(server_matches_acl_event("evil.com", e))
-        self.assertFalse(server_matches_acl_event("EVIL.COM", e))
+        server_acl_evalutor = server_acl_evaluator_from_event(e)
 
-        self.assertTrue(server_matches_acl_event("evil.com.au", e))
-        self.assertTrue(server_matches_acl_event("honestly.not.evil.com", e))
+        self.assertFalse(server_acl_evalutor.server_matches_acl_event("evil.com"))
+        self.assertFalse(server_acl_evalutor.server_matches_acl_event("EVIL.COM"))
+
+        self.assertTrue(server_acl_evalutor.server_matches_acl_event("evil.com.au"))
+        self.assertTrue(
+            server_acl_evalutor.server_matches_acl_event("honestly.not.evil.com")
+        )
 
     def test_block_ip_literals(self) -> None:
         e = _create_acl_event({"allow_ip_literals": False, "allow": ["*"]})
         logging.info("ACL event: %s", e.content)
 
-        self.assertFalse(server_matches_acl_event("1.2.3.4", e))
-        self.assertTrue(server_matches_acl_event("1a.2.3.4", e))
-        self.assertFalse(server_matches_acl_event("[1:2::]", e))
-        self.assertTrue(server_matches_acl_event("1:2:3:4", e))
+        server_acl_evalutor = server_acl_evaluator_from_event(e)
+
+        self.assertFalse(server_acl_evalutor.server_matches_acl_event("1.2.3.4"))
+        self.assertTrue(server_acl_evalutor.server_matches_acl_event("1a.2.3.4"))
+        self.assertFalse(server_acl_evalutor.server_matches_acl_event("[1:2::]"))
+        self.assertTrue(server_acl_evalutor.server_matches_acl_event("1:2:3:4"))
 
     def test_wildcard_matching(self) -> None:
         e = _create_acl_event({"allow": ["good*.com"]})
+
+        server_acl_evalutor = server_acl_evaluator_from_event(e)
+
         self.assertTrue(
-            server_matches_acl_event("good.com", e),
+            server_acl_evalutor.server_matches_acl_event("good.com"),
             "* matches 0 characters",
         )
         self.assertTrue(
-            server_matches_acl_event("GOOD.COM", e),
+            server_acl_evalutor.server_matches_acl_event("GOOD.COM"),
             "pattern is case-insensitive",
         )
         self.assertTrue(
-            server_matches_acl_event("good.aa.com", e),
+            server_acl_evalutor.server_matches_acl_event("good.aa.com"),
             "* matches several characters, including '.'",
         )
         self.assertFalse(
-            server_matches_acl_event("ishgood.com", e),
+            server_acl_evalutor.server_matches_acl_event("ishgood.com"),
             "pattern does not allow prefixes",
         )