Reject invalid server names (#3480)

Make sure that server_names used in auth headers are sane, and reject them with
a sensible error code, before they disappear off into the depths of the system.

changelog.d/3480.feature

@@ -0,0 +1 @@
+Reject invalid server names in federation requests

synapse/federation/transport/server.py

@@ -18,6 +18,7 @@ from twisted.internet import defer
 
 from synapse.api.urls import FEDERATION_PREFIX as PREFIX
 from synapse.api.errors import Codes, SynapseError, FederationDeniedError
+from synapse.http.endpoint import parse_server_name
 from synapse.http.server import JsonResource
 from synapse.http.servlet import (
     parse_json_object_from_request, parse_integer_from_args, parse_string_from_args,
@@ -99,26 +100,6 @@ class Authenticator(object):
 
         origin = None
 
-        def parse_auth_header(header_str):
-            try:
-                params = auth.split(" ")[1].split(",")
-                param_dict = dict(kv.split("=") for kv in params)
-
-                def strip_quotes(value):
-                    if value.startswith("\""):
-                        return value[1:-1]
-                    else:
-                        return value
-
-                origin = strip_quotes(param_dict["origin"])
-                key = strip_quotes(param_dict["key"])
-                sig = strip_quotes(param_dict["sig"])
-                return (origin, key, sig)
-            except Exception:
-                raise AuthenticationError(
-                    400, "Malformed Authorization header", Codes.UNAUTHORIZED
-                )
-
         auth_headers = request.requestHeaders.getRawHeaders(b"Authorization")
 
         if not auth_headers:
@@ -127,8 +108,8 @@ class Authenticator(object):
             )
 
         for auth in auth_headers:
-            if auth.startswith("X-Matrix"):
-                (origin, key, sig) = parse_auth_header(auth)
+            if auth.startswith(b"X-Matrix"):
+                (origin, key, sig) = _parse_auth_header(auth)
                 json_request["origin"] = origin
                 json_request["signatures"].setdefault(origin, {})[key] = sig
 
@@ -165,6 +146,47 @@ class Authenticator(object):
             logger.exception("Error resetting retry timings on %s", origin)
 
 
+def _parse_auth_header(header_bytes):
+    """Parse an X-Matrix auth header
+
+    Args:
+        header_bytes (bytes): header value
+
+    Returns:
+        Tuple[str, str, str]: origin, key id, signature.
+
+    Raises:
+        AuthenticationError if the header could not be parsed
+    """
+    try:
+        header_str = header_bytes.decode('utf-8')
+        params = header_str.split(" ")[1].split(",")
+        param_dict = dict(kv.split("=") for kv in params)
+
+        def strip_quotes(value):
+            if value.startswith(b"\""):
+                return value[1:-1]
+            else:
+                return value
+
+        origin = strip_quotes(param_dict["origin"])
+        # ensure that the origin is a valid server name
+        parse_server_name(origin)
+
+        key = strip_quotes(param_dict["key"])
+        sig = strip_quotes(param_dict["sig"])
+        return origin, key, sig
+    except Exception as e:
+        logger.warn(
+            "Error parsing auth header '%s': %s",
+            header_bytes.decode('ascii', 'replace'),
+            e,
+        )
+        raise AuthenticationError(
+            400, "Malformed Authorization header", Codes.UNAUTHORIZED,
+        )
+
+
 class BaseFederationServlet(object):
     REQUIRE_AUTH = True
 

synapse/http/endpoint.py

@@ -38,6 +38,36 @@ _Server = collections.namedtuple(
 )
 
 
+def parse_server_name(server_name):
+    """Split a server name into host/port parts.
+
+    Does some basic sanity checking of the
+
+    Args:
+        server_name (str): server name to parse
+
+    Returns:
+        Tuple[str, int|None]: host/port parts.
+
+    Raises:
+        ValueError if the server name could not be parsed.
+    """
+    try:
+        if server_name[-1] == ']':
+            # ipv6 literal, hopefully
+            if server_name[0] != '[':
+                raise Exception()
+
+            return server_name, None
+
+        domain_port = server_name.rsplit(":", 1)
+        domain = domain_port[0]
+        port = int(domain_port[1]) if domain_port[1:] else None
+        return domain, port
+    except Exception:
+        raise ValueError("Invalid server name '%s'" % server_name)
+
+
 def matrix_federation_endpoint(reactor, destination, ssl_context_factory=None,
                                timeout=None):
     """Construct an endpoint for the given matrix destination.
@@ -50,9 +80,7 @@ def matrix_federation_endpoint(reactor, destination, ssl_context_factory=None,
         timeout (int): connection timeout in seconds
     """
 
-    domain_port = destination.split(":")
-    domain = domain_port[0]
-    port = int(domain_port[1]) if domain_port[1:] else None
+    domain, port = parse_server_name(destination)
 
     endpoint_kw_args = {}
 

tests/http/test_endpoint.py

@@ -0,0 +1,46 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# 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 synapse.http.endpoint import parse_server_name
+from tests import unittest
+
+
+class ServerNameTestCase(unittest.TestCase):
+    def test_parse_server_name(self):
+        test_data = {
+            'localhost': ('localhost', None),
+            'my-example.com:1234': ('my-example.com', 1234),
+            '1.2.3.4': ('1.2.3.4', None),
+            '[0abc:1def::1234]': ('[0abc:1def::1234]', None),
+            '1.2.3.4:1': ('1.2.3.4', 1),
+            '[0abc:1def::1234]:8080': ('[0abc:1def::1234]', 8080),
+        }
+
+        for i, o in test_data.items():
+            self.assertEqual(parse_server_name(i), o)
+
+    def test_parse_bad_server_names(self):
+        test_data = [
+            "",  # empty
+            "localhost:http",  # non-numeric port
+            "1234]",  # smells like ipv6 literal but isn't
+        ]
+        for i in test_data:
+            try:
+                parse_server_name(i)
+                self.fail(
+                    "Expected parse_server_name(\"%s\") to throw" % i,
+                )
+            except ValueError:
+                pass