Merge remote-tracking branch 'upstream/release-v1.25.0'

synapse/http/client.py

@@ -125,7 +125,7 @@ def _make_scheduler(reactor):
     return _scheduler
 
 
-class IPBlacklistingResolver:
+class _IPBlacklistingResolver:
     """
     A proxy for reactor.nameResolver which only produces non-blacklisted IP
     addresses, preventing DNS rebinding attacks on URL preview.
@@ -199,6 +199,35 @@ class IPBlacklistingResolver:
         return r
 
 
+@implementer(IReactorPluggableNameResolver)
+class BlacklistingReactorWrapper:
+    """
+    A Reactor wrapper which will prevent DNS resolution to blacklisted IP
+    addresses, to prevent DNS rebinding.
+    """
+
+    def __init__(
+        self,
+        reactor: IReactorPluggableNameResolver,
+        ip_whitelist: Optional[IPSet],
+        ip_blacklist: IPSet,
+    ):
+        self._reactor = reactor
+
+        # We need to use a DNS resolver which filters out blacklisted IP
+        # addresses, to prevent DNS rebinding.
+        self._nameResolver = _IPBlacklistingResolver(
+            self._reactor, ip_whitelist, ip_blacklist
+        )
+
+    def __getattr__(self, attr: str) -> Any:
+        # Passthrough to the real reactor except for the DNS resolver.
+        if attr == "nameResolver":
+            return self._nameResolver
+        else:
+            return getattr(self._reactor, attr)
+
+
 class BlacklistingAgentWrapper(Agent):
     """
     An Agent wrapper which will prevent access to IP addresses being accessed
@@ -293,22 +322,11 @@ class SimpleHttpClient:
         self.user_agent = self.user_agent.encode("ascii")
 
         if self._ip_blacklist:
-            real_reactor = hs.get_reactor()
             # If we have an IP blacklist, we need to use a DNS resolver which
             # filters out blacklisted IP addresses, to prevent DNS rebinding.
-            nameResolver = IPBlacklistingResolver(
-                real_reactor, self._ip_whitelist, self._ip_blacklist
+            self.reactor = BlacklistingReactorWrapper(
+                hs.get_reactor(), self._ip_whitelist, self._ip_blacklist
             )
-
-            @implementer(IReactorPluggableNameResolver)
-            class Reactor:
-                def __getattr__(_self, attr):
-                    if attr == "nameResolver":
-                        return nameResolver
-                    else:
-                        return getattr(real_reactor, attr)
-
-            self.reactor = Reactor()
         else:
             self.reactor = hs.get_reactor()
 
@@ -703,11 +721,14 @@ class SimpleHttpClient:
 
         try:
             length = await make_deferred_yieldable(
-                readBodyToFile(response, output_stream, max_size)
+                read_body_with_max_size(response, output_stream, max_size)
+            )
+        except BodyExceededMaxSize:
+            SynapseError(
+                502,
+                "Requested file is too large > %r bytes" % (max_size,),
+                Codes.TOO_LARGE,
             )
-        except SynapseError:
-            # This can happen e.g. because the body is too large.
-            raise
         except Exception as e:
             raise SynapseError(502, ("Failed to download remote body: %s" % e)) from e
 
@@ -731,7 +752,11 @@ def _timeout_to_request_timed_out_error(f: Failure):
     return f
 
 
-class _ReadBodyToFileProtocol(protocol.Protocol):
+class BodyExceededMaxSize(Exception):
+    """The maximum allowed size of the HTTP body was exceeded."""
+
+
+class _ReadBodyWithMaxSizeProtocol(protocol.Protocol):
     def __init__(
         self, stream: BinaryIO, deferred: defer.Deferred, max_size: Optional[int]
     ):
@@ -744,13 +769,7 @@ class _ReadBodyToFileProtocol(protocol.Protocol):
         self.stream.write(data)
         self.length += len(data)
         if self.max_size is not None and self.length >= self.max_size:
-            self.deferred.errback(
-                SynapseError(
-                    502,
-                    "Requested file is too large > %r bytes" % (self.max_size,),
-                    Codes.TOO_LARGE,
-                )
-            )
+            self.deferred.errback(BodyExceededMaxSize())
             self.deferred = defer.Deferred()
             self.transport.loseConnection()
 
@@ -765,12 +784,15 @@ class _ReadBodyToFileProtocol(protocol.Protocol):
             self.deferred.errback(reason)
 
 
-def readBodyToFile(
+def read_body_with_max_size(
     response: IResponse, stream: BinaryIO, max_size: Optional[int]
 ) -> defer.Deferred:
     """
     Read a HTTP response body to a file-object. Optionally enforcing a maximum file size.
 
+    If the maximum file size is reached, the returned Deferred will resolve to a
+    Failure with a BodyExceededMaxSize exception.
+
     Args:
         response: The HTTP response to read from.
         stream: The file-object to write to.
@@ -781,7 +803,7 @@ def readBodyToFile(
     """
 
     d = defer.Deferred()
-    response.deliverBody(_ReadBodyToFileProtocol(stream, d, max_size))
+    response.deliverBody(_ReadBodyWithMaxSizeProtocol(stream, d, max_size))
     return d