add a url_preview_ip_range_whitelist config param so we can whitelist the matrix.org IP space

synapse/config/repository.py

@@ -100,6 +100,11 @@ class ContentRepositoryConfig(Config):
                     "to work"
                 )
 
+            if "url_preview_ip_range_whitelist" in config:
+                self.url_preview_ip_range_whitelist = IPSet(
+                    config["url_preview_ip_range_whitelist"]
+                )
+
             if "url_preview_url_blacklist" in config:
                 self.url_preview_url_blacklist = config["url_preview_url_blacklist"]
 
@@ -162,6 +167,15 @@ class ContentRepositoryConfig(Config):
         # - '10.0.0.0/8'
         # - '172.16.0.0/12'
         # - '192.168.0.0/16'
+        #
+        # List of IP address CIDR ranges that the URL preview spider is allowed
+        # to access even if they are specified in url_preview_ip_range_blacklist.
+        # This is useful for specifying exceptions to wide-ranging blacklisted
+        # target IP ranges - e.g. for enabling URL previews for a specific private
+        # website only visible in your network.
+        #
+        # url_preview_ip_range_whitelist:
+        # - '192.168.1.1'
 
         # Optional list of URL matches that the URL preview spider is
         # denied from accessing.  You should use url_preview_ip_range_blacklist

synapse/http/client.py

@@ -380,13 +380,15 @@ class CaptchaServerHttpClient(SimpleHttpClient):
 class SpiderEndpointFactory(object):
     def __init__(self, hs):
         self.blacklist = hs.config.url_preview_ip_range_blacklist
+        if hasattr(hs.config, "url_preview_ip_range_whitelist"):
+            self.whitelist = hs.config.url_preview_ip_range_whitelist
         self.policyForHTTPS = hs.get_http_client_context_factory()
 
     def endpointForURI(self, uri):
         logger.info("Getting endpoint for %s", uri.toBytes())
         if uri.scheme == "http":
             return SpiderEndpoint(
-                reactor, uri.host, uri.port, self.blacklist,
+                reactor, uri.host, uri.port, self.blacklist, self.whitelist,
                 endpoint=TCP4ClientEndpoint,
                 endpoint_kw_args={
                     'timeout': 15
@@ -395,7 +397,7 @@ class SpiderEndpointFactory(object):
         elif uri.scheme == "https":
             tlsPolicy = self.policyForHTTPS.creatorForNetloc(uri.host, uri.port)
             return SpiderEndpoint(
-                reactor, uri.host, uri.port, self.blacklist,
+                reactor, uri.host, uri.port, self.blacklist, self.whitelist,
                 endpoint=SSL4ClientEndpoint,
                 endpoint_kw_args={
                     'sslContextFactory': tlsPolicy,

synapse/http/endpoint.py

@@ -79,12 +79,13 @@ class SpiderEndpoint(object):
     """An endpoint which refuses to connect to blacklisted IP addresses
     Implements twisted.internet.interfaces.IStreamClientEndpoint.
     """
-    def __init__(self, reactor, host, port, blacklist,
+    def __init__(self, reactor, host, port, blacklist, whitelist,
                  endpoint=TCP4ClientEndpoint, endpoint_kw_args={}):
         self.reactor = reactor
         self.host = host
         self.port = port
         self.blacklist = blacklist
+        self.whitelist = whitelist
         self.endpoint = endpoint
         self.endpoint_kw_args = endpoint_kw_args
 
@@ -93,7 +94,10 @@ class SpiderEndpoint(object):
         address = yield self.reactor.resolve(self.host)
 
         from netaddr import IPAddress
-        if IPAddress(address) in self.blacklist:
+        ip_address = IPAddress(address)
+
+        if ip_address in self.blacklist:
+            if self.whitelist is None or ip_address not in self.whitelist:
                 raise ConnectError(
                     "Refusing to spider blacklisted IP address %s" % address
                 )