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.

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