Convert blacklisted IPv4 addresses to compatible IPv6 addresses. (#9240)

Also add a few more IP ranges to the default blacklist.

2 files changed, 91 insertions, 27 deletions

diff --git a/synapse/config/repository.py b/synapse/config/repository.py
index 850ac3ebd6..fcaea8fb93 100644
--- a/synapse/config/repository.py
+++ b/synapse/config/repository.py
@@ -17,9 +17,7 @@ import os
 from collections import namedtuple
 from typing import Dict, List
 
-from netaddr import IPSet
-
-from synapse.config.server import DEFAULT_IP_RANGE_BLACKLIST
+from synapse.config.server import DEFAULT_IP_RANGE_BLACKLIST, generate_ip_set
 from synapse.python_dependencies import DependencyException, check_requirements
 from synapse.util.module_loader import load_module
 
@@ -187,16 +185,17 @@ class ContentRepositoryConfig(Config):
                     "to work"
                 )
 
-            self.url_preview_ip_range_blacklist = IPSet(
-                config["url_preview_ip_range_blacklist"]
-            )
-
             # we always blacklist '0.0.0.0' and '::', which are supposed to be
             # unroutable addresses.
-            self.url_preview_ip_range_blacklist.update(["0.0.0.0", "::"])
+            self.url_preview_ip_range_blacklist = generate_ip_set(
+                config["url_preview_ip_range_blacklist"],
+                ["0.0.0.0", "::"],
+                config_path=("url_preview_ip_range_blacklist",),
+            )
 
-            self.url_preview_ip_range_whitelist = IPSet(
-                config.get("url_preview_ip_range_whitelist", ())
+            self.url_preview_ip_range_whitelist = generate_ip_set(
+                config.get("url_preview_ip_range_whitelist", ()),
+                config_path=("url_preview_ip_range_whitelist",),
             )
 
             self.url_preview_url_blacklist = config.get("url_preview_url_blacklist", ())
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 47a0370173..b5e82ba3d0 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -15,6 +15,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import itertools
 import logging
 import os.path
 import re
@@ -23,7 +24,7 @@ from typing import Any, Dict, Iterable, List, Optional, Set
 
 import attr
 import yaml
-from netaddr import IPSet
+from netaddr import AddrFormatError, IPNetwork, IPSet
 
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.util.stringutils import parse_and_validate_server_name
@@ -40,6 +41,66 @@ logger = logging.Logger(__name__)
 # in the list.
 DEFAULT_BIND_ADDRESSES = ["::", "0.0.0.0"]
 
+
+def _6to4(network: IPNetwork) -> IPNetwork:
+    """Convert an IPv4 network into a 6to4 IPv6 network per RFC 3056."""
+
+    # 6to4 networks consist of:
+    # * 2002 as the first 16 bits
+    # * The first IPv4 address in the network hex-encoded as the next 32 bits
+    # * The new prefix length needs to include the bits from the 2002 prefix.
+    hex_network = hex(network.first)[2:]
+    hex_network = ("0" * (8 - len(hex_network))) + hex_network
+    return IPNetwork(
+        "2002:%s:%s::/%d" % (hex_network[:4], hex_network[4:], 16 + network.prefixlen,)
+    )
+
+
+def generate_ip_set(
+    ip_addresses: Optional[Iterable[str]],
+    extra_addresses: Optional[Iterable[str]] = None,
+    config_path: Optional[Iterable[str]] = None,
+) -> IPSet:
+    """
+    Generate an IPSet from a list of IP addresses or CIDRs.
+
+    Additionally, for each IPv4 network in the list of IP addresses, also
+    includes the corresponding IPv6 networks.
+
+    This includes:
+
+    * IPv4-Compatible IPv6 Address (see RFC 4291, section 2.5.5.1)
+    * IPv4-Mapped IPv6 Address (see RFC 4291, section 2.5.5.2)
+    * 6to4 Address (see RFC 3056, section 2)
+
+    Args:
+        ip_addresses: An iterable of IP addresses or CIDRs.
+        extra_addresses: An iterable of IP addresses or CIDRs.
+        config_path: The path in the configuration for error messages.
+
+    Returns:
+        A new IP set.
+    """
+    result = IPSet()
+    for ip in itertools.chain(ip_addresses or (), extra_addresses or ()):
+        try:
+            network = IPNetwork(ip)
+        except AddrFormatError as e:
+            raise ConfigError(
+                "Invalid IP range provided: %s." % (ip,), config_path
+            ) from e
+        result.add(network)
+
+        # It is possible that these already exist in the set, but that's OK.
+        if ":" not in str(network):
+            result.add(IPNetwork(network).ipv6(ipv4_compatible=True))
+            result.add(IPNetwork(network).ipv6(ipv4_compatible=False))
+            result.add(_6to4(network))
+
+    return result
+
+
+# IP ranges that are considered private / unroutable / don't make sense.
 DEFAULT_IP_RANGE_BLACKLIST = [
     # Localhost
     "127.0.0.0/8",
@@ -53,6 +114,8 @@ DEFAULT_IP_RANGE_BLACKLIST = [
     "192.0.0.0/24",
     # Link-local networks.
     "169.254.0.0/16",
+    # Formerly used for 6to4 relay.
+    "192.88.99.0/24",
     # Testing networks.
     "198.18.0.0/15",
     "192.0.2.0/24",
@@ -66,6 +129,12 @@ DEFAULT_IP_RANGE_BLACKLIST = [
     "fe80::/10",
     # Unique local addresses.
     "fc00::/7",
+    # Testing networks.
+    "2001:db8::/32",
+    # Multicast.
+    "ff00::/8",
+    # Site-local addresses
+    "fec0::/10",
 ]
 
 DEFAULT_ROOM_VERSION = "6"
@@ -294,17 +363,15 @@ class ServerConfig(Config):
         )
 
         # Attempt to create an IPSet from the given ranges
-        try:
-            self.ip_range_blacklist = IPSet(ip_range_blacklist)
-        except Exception as e:
-            raise ConfigError("Invalid range(s) provided in ip_range_blacklist.") from e
+
         # Always blacklist 0.0.0.0, ::
-        self.ip_range_blacklist.update(["0.0.0.0", "::"])
+        self.ip_range_blacklist = generate_ip_set(
+            ip_range_blacklist, ["0.0.0.0", "::"], config_path=("ip_range_blacklist",)
+        )
 
-        try:
-            self.ip_range_whitelist = IPSet(config.get("ip_range_whitelist", ()))
-        except Exception as e:
-            raise ConfigError("Invalid range(s) provided in ip_range_whitelist.") from e
+        self.ip_range_whitelist = generate_ip_set(
+            config.get("ip_range_whitelist", ()), config_path=("ip_range_whitelist",)
+        )
 
         # The federation_ip_range_blacklist is used for backwards-compatibility
         # and only applies to federation and identity servers. If it is not given,
@@ -312,14 +379,12 @@ class ServerConfig(Config):
         federation_ip_range_blacklist = config.get(
             "federation_ip_range_blacklist", ip_range_blacklist
         )
-        try:
-            self.federation_ip_range_blacklist = IPSet(federation_ip_range_blacklist)
-        except Exception as e:
-            raise ConfigError(
-                "Invalid range(s) provided in federation_ip_range_blacklist."
-            ) from e
         # Always blacklist 0.0.0.0, ::
-        self.federation_ip_range_blacklist.update(["0.0.0.0", "::"])
+        self.federation_ip_range_blacklist = generate_ip_set(
+            federation_ip_range_blacklist,
+            ["0.0.0.0", "::"],
+            config_path=("federation_ip_range_blacklist",),
+        )
 
         self.start_pushers = config.get("start_pushers", True)