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Add a maximum size for well-known lookups. (#8950)

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Patrick Cloke 2020-12-16 17:25:24 -05:00 committed by GitHub
parent e1b8e37f93
commit ff5c4da128
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5 changed files with 80 additions and 18 deletions
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1
changelog.d/8950.misc Normal file
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@ -0,0 +1 @@
Add a maximum size of 50 kilobytes to .well-known lookups.

32
synapse/http/client.py
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@ -720,11 +720,14 @@ 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
@ -748,7 +751,11 @@ 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]
):
@ -761,13 +768,7 @@ 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()
@ -782,12 +783,15 @@ 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.
@ -798,7 +802,7 @@ def readBodyToFile(
"""
d = defer.Deferred()
response.deliverBody(_ReadBodyToFileProtocol(stream, d, max_size))
response.deliverBody(_ReadBodyWithMaxSizeProtocol(stream, d, max_size))
return d

25
synapse/http/federation/well_known_resolver.py
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@ -15,17 +15,19 @@
import logging
import random
import time
from io import BytesIO
from typing import Callable, Dict, Optional, Tuple
import attr
from twisted.internet import defer
from twisted.internet.interfaces import IReactorTime
from twisted.web.client import RedirectAgent, readBody
from twisted.web.client import RedirectAgent
from twisted.web.http import stringToDatetime
from twisted.web.http_headers import Headers
from twisted.web.iweb import IAgent, IResponse
from synapse.http.client import BodyExceededMaxSize, read_body_with_max_size
from synapse.logging.context import make_deferred_yieldable
from synapse.util import Clock, json_decoder
from synapse.util.caches.ttlcache import TTLCache
@ -53,6 +55,9 @@ WELL_KNOWN_MAX_CACHE_PERIOD = 48 * 3600
# lower bound for .well-known cache period
WELL_KNOWN_MIN_CACHE_PERIOD = 5 * 60
# The maximum size (in bytes) to allow a well-known file to be.
WELL_KNOWN_MAX_SIZE = 50 * 1024 # 50 KiB
# Attempt to refetch a cached well-known N% of the TTL before it expires.
# e.g. if set to 0.2 and we have a cached entry with a TTL of 5mins, then
# we'll start trying to refetch 1 minute before it expires.
@ -229,6 +234,9 @@ class WellKnownResolver:
server_name: name of the server, from the requested url
retry: Whether to retry the request if it fails.
Raises:
_FetchWellKnownFailure if we fail to lookup a result
Returns:
Returns the response object and body. Response may be a non-200 response.
"""
@ -250,7 +258,11 @@ class WellKnownResolver:
b"GET", uri, headers=Headers(headers)
)
)
body = await make_deferred_yieldable(readBody(response))
body_stream = BytesIO()
await make_deferred_yieldable(
read_body_with_max_size(response, body_stream, WELL_KNOWN_MAX_SIZE)
)
body = body_stream.getvalue()
if 500 <= response.code < 600:
raise Exception("Non-200 response %s" % (response.code,))
@ -259,6 +271,15 @@ class WellKnownResolver:
except defer.CancelledError:
# Bail if we've been cancelled
raise
except BodyExceededMaxSize:
# If the well-known file was too large, do not keep attempting
# to download it, but consider it a temporary error.
logger.warning(
"Requested .well-known file for %s is too large > %r bytes",
server_name.decode("ascii"),
WELL_KNOWN_MAX_SIZE,
)
raise _FetchWellKnownFailure(temporary=True)
except Exception as e:
if not retry or i >= WELL_KNOWN_RETRY_ATTEMPTS:
logger.info("Error fetching %s: %s", uri_str, e)

13
synapse/http/matrixfederationclient.py
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@ -37,16 +37,19 @@ from twisted.web.iweb import IBodyProducer, IResponse
import synapse.metrics
import synapse.util.retryutils
from synapse.api.errors import (
Codes,
FederationDeniedError,
HttpResponseException,
RequestSendFailed,
SynapseError,
)
from synapse.http import QuieterFileBodyProducer
from synapse.http.client import (
BlacklistingAgentWrapper,
BlacklistingReactorWrapper,
BodyExceededMaxSize,
encode_query_args,
readBodyToFile,
read_body_with_max_size,
)
from synapse.http.federation.matrix_federation_agent import MatrixFederationAgent
from synapse.logging.context import make_deferred_yieldable
@ -975,9 +978,15 @@ class MatrixFederationHttpClient:
headers = dict(response.headers.getAllRawHeaders())
try:
d = readBodyToFile(response, output_stream, max_size)
d = read_body_with_max_size(response, output_stream, max_size)
d.addTimeout(self.default_timeout, self.reactor)
length = await make_deferred_yieldable(d)
except BodyExceededMaxSize:
msg = "Requested file is too large > %r bytes" % (max_size,)
logger.warning(
"{%s} [%s] %s", request.txn_id, request.destination, msg,
)
SynapseError(502, msg, Codes.TOO_LARGE)
except Exception as e:
logger.warning(
"{%s} [%s] Error reading response: %s",

27
tests/http/federation/test_matrix_federation_agent.py
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@ -36,6 +36,7 @@ from synapse.crypto.context_factory import FederationPolicyForHTTPS
from synapse.http.federation.matrix_federation_agent import MatrixFederationAgent
from synapse.http.federation.srv_resolver import Server
from synapse.http.federation.well_known_resolver import (
WELL_KNOWN_MAX_SIZE,
WellKnownResolver,
_cache_period_from_headers,
)
@ -1107,6 +1108,32 @@ class MatrixFederationAgentTests(unittest.TestCase):
r = self.successResultOf(fetch_d)
self.assertEqual(r.delegated_server, None)
def test_well_known_too_large(self):
"""A well-known query that returns a result which is too large should be rejected."""
self.reactor.lookups["testserv"] = "1.2.3.4"
fetch_d = defer.ensureDeferred(
self.well_known_resolver.get_well_known(b"testserv")
)
# there should be an attempt to connect on port 443 for the .well-known
clients = self.reactor.tcpClients
self.assertEqual(len(clients), 1)
(host, port, client_factory, _timeout, _bindAddress) = clients.pop(0)
self.assertEqual(host, "1.2.3.4")
self.assertEqual(port, 443)
self._handle_well_known_connection(
client_factory,
expected_sni=b"testserv",
response_headers={b"Cache-Control": b"max-age=1000"},
content=b'{ "m.server": "' + (b"a" * WELL_KNOWN_MAX_SIZE) + b'" }',
)
# The result is sucessful, but disabled delegation.
r = self.successResultOf(fetch_d)
self.assertIsNone(r.delegated_server)
def test_srv_fallbacks(self):
"""Test that other SRV results are tried if the first one fails.
"""