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URL preview blacklisting fixes (#5155)

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Prevents a SynapseError being raised inside of a IResolutionReceiver and instead opts to just return 0 results. This thus means that we have to lump a failed lookup and a blacklisted lookup together with the same error message, but the substitute should be generic enough to cover both cases.
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Andrew Morgan 2019-05-10 10:32:44 -07:00 committed by GitHub
parent c2bb7476c9
commit 2f48c4e1ae
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4 changed files with 47 additions and 31 deletions
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1
changelog.d/5155.misc Normal file
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@ -0,0 +1 @@
Prevent an exception from being raised in a IResolutionReceiver and use a more generic error message for blacklisted URL previews.

45
synapse/http/client.py
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@ -90,9 +90,32 @@ class IPBlacklistingResolver(object):
def resolveHostName(self, recv, hostname, portNumber=0):
r = recv()
d = defer.Deferred()
addresses = []
def _callback():
r.resolutionBegan(None)
has_bad_ip = False
for i in addresses:
ip_address = IPAddress(i.host)
if check_against_blacklist(
ip_address, self._ip_whitelist, self._ip_blacklist
):
logger.info(
"Dropped %s from DNS resolution to %s due to blacklist" %
(ip_address, hostname)
)
has_bad_ip = True
# if we have a blacklisted IP, we'd like to raise an error to block the
# request, but all we can really do from here is claim that there were no
# valid results.
if not has_bad_ip:
for i in addresses:
r.addressResolved(i)
r.resolutionComplete()
@provider(IResolutionReceiver)
class EndpointReceiver(object):
@staticmethod
@ -101,34 +124,16 @@ class IPBlacklistingResolver(object):
@staticmethod
def addressResolved(address):
ip_address = IPAddress(address.host)
if check_against_blacklist(
ip_address, self._ip_whitelist, self._ip_blacklist
):
logger.info(
"Dropped %s from DNS resolution to %s" % (ip_address, hostname)
)
raise SynapseError(403, "IP address blocked by IP blacklist entry")
addresses.append(address)
@staticmethod
def resolutionComplete():
d.callback(addresses)
_callback()
self._reactor.nameResolver.resolveHostName(
EndpointReceiver, hostname, portNumber=portNumber
)
def _callback(addrs):
r.resolutionBegan(None)
for i in addrs:
r.addressResolved(i)
r.resolutionComplete()
d.addCallback(_callback)
return r

10
synapse/rest/media/v1/preview_url_resource.py
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@ -31,6 +31,7 @@ from six.moves import urllib_parse as urlparse
from canonicaljson import json
from twisted.internet import defer
from twisted.internet.error import DNSLookupError
from twisted.web.resource import Resource
from twisted.web.server import NOT_DONE_YET
@ -328,9 +329,18 @@ class PreviewUrlResource(Resource):
# handler will return a SynapseError to the client instead of
# blank data or a 500.
raise
except DNSLookupError:
# DNS lookup returned no results
# Note: This will also be the case if one of the resolved IP
# addresses is blacklisted
raise SynapseError(
502, "DNS resolution failure during URL preview generation",
Codes.UNKNOWN
)
except Exception as e:
# FIXME: pass through 404s and other error messages nicely
logger.warn("Error downloading %s: %r", url, e)
raise SynapseError(
500, "Failed to download content: %s" % (
traceback.format_exception_only(sys.exc_info()[0], e),

22
tests/rest/media/v1/test_url_preview.py
View File

@ -297,12 +297,12 @@ class URLPreviewTests(unittest.HomeserverTestCase):
# No requests made.
self.assertEqual(len(self.reactor.tcpClients), 0)
self.assertEqual(channel.code, 403)
self.assertEqual(channel.code, 502)
self.assertEqual(
channel.json_body,
{
'errcode': 'M_UNKNOWN',
'error': 'IP address blocked by IP blacklist entry',
'error': 'DNS resolution failure during URL preview generation',
},
)
@ -318,12 +318,12 @@ class URLPreviewTests(unittest.HomeserverTestCase):
request.render(self.preview_url)
self.pump()
self.assertEqual(channel.code, 403)
self.assertEqual(channel.code, 502)
self.assertEqual(
channel.json_body,
{
'errcode': 'M_UNKNOWN',
'error': 'IP address blocked by IP blacklist entry',
'error': 'DNS resolution failure during URL preview generation',
},
)
@ -339,7 +339,6 @@ class URLPreviewTests(unittest.HomeserverTestCase):
# No requests made.
self.assertEqual(len(self.reactor.tcpClients), 0)
self.assertEqual(channel.code, 403)
self.assertEqual(
channel.json_body,
{
@ -347,6 +346,7 @@ class URLPreviewTests(unittest.HomeserverTestCase):
'error': 'IP address blocked by IP blacklist entry',
},
)
self.assertEqual(channel.code, 403)
def test_blacklisted_ip_range_direct(self):
"""
@ -414,12 +414,12 @@ class URLPreviewTests(unittest.HomeserverTestCase):
)
request.render(self.preview_url)
self.pump()
self.assertEqual(channel.code, 403)
self.assertEqual(channel.code, 502)
self.assertEqual(
channel.json_body,
{
'errcode': 'M_UNKNOWN',
'error': 'IP address blocked by IP blacklist entry',
'error': 'DNS resolution failure during URL preview generation',
},
)
@ -439,12 +439,12 @@ class URLPreviewTests(unittest.HomeserverTestCase):
# No requests made.
self.assertEqual(len(self.reactor.tcpClients), 0)
self.assertEqual(channel.code, 403)
self.assertEqual(channel.code, 502)
self.assertEqual(
channel.json_body,
{
'errcode': 'M_UNKNOWN',
'error': 'IP address blocked by IP blacklist entry',
'error': 'DNS resolution failure during URL preview generation',
},
)
@ -460,11 +460,11 @@ class URLPreviewTests(unittest.HomeserverTestCase):
request.render(self.preview_url)
self.pump()
self.assertEqual(channel.code, 403)
self.assertEqual(channel.code, 502)
self.assertEqual(
channel.json_body,
{
'errcode': 'M_UNKNOWN',
'error': 'IP address blocked by IP blacklist entry',
'error': 'DNS resolution failure during URL preview generation',
},
)