Use the federation blacklist for requests to untrusted Identity Servers (#6000)

Uses a SimpleHttpClient instance equipped with the federation_ip_range_blacklist list for requests to identity servers provided by user input. Does not use a blacklist when contacting identity servers specified by account_threepid_delegates. The homeserver trusts the latter and we don't want to prevent homeserver admins from specifying delegates that are on internal IP addresses.

Fixes #5935

5 files changed, 28 insertions, 4 deletions

diff --git a/changelog.d/6000.feature b/changelog.d/6000.feature
new file mode 100644

index 0000000000..0a159bd10d
--- /dev/null
+++ b/changelog.d/6000.feature
@@ -0,0 +1 @@
+Apply the federation blacklist to requests to identity servers.
\ No newline at end of file
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml

index 61d9f09a99..e53b979c35 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -110,6 +110,9 @@ pid_file: DATADIR/homeserver.pid
 # blacklist IP address CIDR ranges. If this option is not specified, or
 # specified with an empty list, no ip range blacklist will be enforced.
 #
+# As of Synapse v1.4.0 this option also affects any outbound requests to identity
+# servers provided by user input.
+#
 # (0.0.0.0 and :: are always blacklisted, whether or not they are explicitly
 # listed here, since they correspond to unroutable addresses.)
 #
diff --git a/synapse/config/server.py b/synapse/config/server.py

index 7f8d315954..419787a89c 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -545,6 +545,9 @@ class ServerConfig(Config):
         # blacklist IP address CIDR ranges. If this option is not specified, or
         # specified with an empty list, no ip range blacklist will be enforced.
         #
+        # As of Synapse v1.4.0 this option also affects any outbound requests to identity
+        # servers provided by user input.
+        #
         # (0.0.0.0 and :: are always blacklisted, whether or not they are explicitly
         # listed here, since they correspond to unroutable addresses.)
         #
diff --git a/synapse/handlers/identity.py b/synapse/handlers/identity.py

index af6f591942..264bdc2189 100644
--- a/synapse/handlers/identity.py
+++ b/synapse/handlers/identity.py
@@ -31,6 +31,7 @@ from synapse.api.errors import (
     SynapseError,
 )
 from synapse.config.emailconfig import ThreepidBehaviour
+from synapse.http.client import SimpleHttpClient
 from synapse.util.stringutils import random_string
 
 from ._base import BaseHandler
@@ -42,7 +43,12 @@ class IdentityHandler(BaseHandler):
     def __init__(self, hs):
         super(IdentityHandler, self).__init__(hs)
 
-        self.http_client = hs.get_simple_http_client()
+        self.http_client = SimpleHttpClient(hs)
+        # We create a blacklisting instance of SimpleHttpClient for contacting identity
+        # servers specified by clients
+        self.blacklisting_http_client = SimpleHttpClient(
+            hs, ip_blacklist=hs.config.federation_ip_range_blacklist
+        )
         self.federation_http_client = hs.get_http_client()
         self.hs = hs
 
@@ -143,7 +149,9 @@ class IdentityHandler(BaseHandler):
             bind_url = "https://%s/_matrix/identity/api/v1/3pid/bind" % (id_server,)
 
         try:
-            data = yield self.http_client.post_json_get_json(
+            # Use the blacklisting http client as this call is only to identity servers
+            # provided by a client
+            data = yield self.blacklisting_http_client.post_json_get_json(
                 bind_url, bind_data, headers=headers
             )
 
@@ -246,7 +254,11 @@ class IdentityHandler(BaseHandler):
         headers = {b"Authorization": auth_headers}
 
         try:
-            yield self.http_client.post_json_get_json(url, content, headers)
+            # Use the blacklisting http client as this call is only to identity servers
+            # provided by a client
+            yield self.blacklisting_http_client.post_json_get_json(
+                url, content, headers
+            )
             changed = True
         except HttpResponseException as e:
             changed = False
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py

index 39df0f128d..94cd0cf3ef 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -31,6 +31,7 @@ from synapse import types
 from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import AuthError, Codes, HttpResponseException, SynapseError
 from synapse.handlers.identity import LookupAlgorithm, create_id_access_token_header
+from synapse.http.client import SimpleHttpClient
 from synapse.types import RoomID, UserID
 from synapse.util.async_helpers import Linearizer
 from synapse.util.distributor import user_joined_room, user_left_room
@@ -62,7 +63,11 @@ class RoomMemberHandler(object):
         self.auth = hs.get_auth()
         self.state_handler = hs.get_state_handler()
         self.config = hs.config
-        self.simple_http_client = hs.get_simple_http_client()
+        # We create a blacklisting instance of SimpleHttpClient for contacting identity
+        # servers specified by clients
+        self.simple_http_client = SimpleHttpClient(
+            hs, ip_blacklist=hs.config.federation_ip_range_blacklist
+        )
 
         self.federation_handler = hs.get_handlers().federation_handler
         self.directory_handler = hs.get_handlers().directory_handler