Fix well-known lookups with the federation certificate whitelist (#5997)

3 files changed, 22 insertions, 15 deletions

diff --git a/synapse/config/tls.py b/synapse/config/tls.py
index c0148aa95c..fc47ba3e9a 100644
--- a/synapse/config/tls.py
+++ b/synapse/config/tls.py
@@ -110,8 +110,15 @@ class TlsConfig(Config):
         # Support globs (*) in whitelist values
         self.federation_certificate_verification_whitelist = []
         for entry in fed_whitelist_entries:
+            try:
+                entry_regex = glob_to_regex(entry.encode("ascii").decode("ascii"))
+            except UnicodeEncodeError:
+                raise ConfigError(
+                    "IDNA domain names are not allowed in the "
+                    "federation_certificate_verification_whitelist: %s" % (entry,)
+                )
+
             # Convert globs to regex
-            entry_regex = glob_to_regex(entry)
             self.federation_certificate_verification_whitelist.append(entry_regex)
 
         # List of custom certificate authorities for federation traffic validation
diff --git a/synapse/crypto/context_factory.py b/synapse/crypto/context_factory.py
index 06e63a96b5..e93f0b3705 100644
--- a/synapse/crypto/context_factory.py
+++ b/synapse/crypto/context_factory.py
@@ -15,7 +15,6 @@
 
 import logging
 
-import idna
 from service_identity import VerificationError
 from service_identity.pyopenssl import verify_hostname, verify_ip_address
 from zope.interface import implementer
@@ -114,14 +113,20 @@ class ClientTLSOptionsFactory(object):
         self._no_verify_ssl_context = self._no_verify_ssl.getContext()
         self._no_verify_ssl_context.set_info_callback(self._context_info_cb)
 
-    def get_options(self, host):
+    def get_options(self, host: bytes):
+
+        # IPolicyForHTTPS.get_options takes bytes, but we want to compare
+        # against the str whitelist. The hostnames in the whitelist are already
+        # IDNA-encoded like the hosts will be here.
+        ascii_host = host.decode("ascii")
+
         # Check if certificate verification has been enabled
         should_verify = self._config.federation_verify_certificates
 
         # Check if we've disabled certificate verification for this host
         if should_verify:
             for regex in self._config.federation_certificate_verification_whitelist:
-                if regex.match(host):
+                if regex.match(ascii_host):
                     should_verify = False
                     break
 
@@ -162,7 +167,7 @@ class SSLClientConnectionCreator(object):
     Replaces twisted.internet.ssl.ClientTLSOptions
     """
 
-    def __init__(self, hostname, ctx, verify_certs):
+    def __init__(self, hostname: bytes, ctx, verify_certs: bool):
         self._ctx = ctx
         self._verifier = ConnectionVerifier(hostname, verify_certs)
 
@@ -190,21 +195,16 @@ class ConnectionVerifier(object):
 
     # This code is based on twisted.internet.ssl.ClientTLSOptions.
 
-    def __init__(self, hostname, verify_certs):
+    def __init__(self, hostname: bytes, verify_certs):
         self._verify_certs = verify_certs
 
-        if isIPAddress(hostname) or isIPv6Address(hostname):
-            self._hostnameBytes = hostname.encode("ascii")
+        _decoded = hostname.decode("ascii")
+        if isIPAddress(_decoded) or isIPv6Address(_decoded):
             self._is_ip_address = True
         else:
-            # twisted's ClientTLSOptions falls back to the stdlib impl here if
-            # idna is not installed, but points out that lacks support for
-            # IDNA2008 (http://bugs.python.org/issue17305).
-            #
-            # We can rely on having idna.
-            self._hostnameBytes = idna.encode(hostname)
             self._is_ip_address = False
 
+        self._hostnameBytes = hostname
         self._hostnameASCII = self._hostnameBytes.decode("ascii")
 
     def verify_context_info_cb(self, ssl_connection, where):
diff --git a/synapse/http/federation/matrix_federation_agent.py b/synapse/http/federation/matrix_federation_agent.py
index feae7de5be..647d26dc56 100644
--- a/synapse/http/federation/matrix_federation_agent.py
+++ b/synapse/http/federation/matrix_federation_agent.py
@@ -217,7 +217,7 @@ class MatrixHostnameEndpoint(object):
             self._tls_options = None
         else:
             self._tls_options = tls_client_options_factory.get_options(
-                self._parsed_uri.host.decode("ascii")
+                self._parsed_uri.host
             )
 
         self._srv_resolver = srv_resolver