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Add check_media_file_for_spam spam checker hook

This commit is contained in:
Erik Johnston 2021-02-03 16:44:16 +00:00
parent afa18f1baa
commit 7e8083eb48
6 changed files with 210 additions and 6 deletions
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1
changelog.d/9311.feature Normal file
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@ -0,0 +1 @@
Add hook to spam checker modules that allow checking file uploads and remote downloads.

3
docs/spam_checker.md
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@ -61,6 +61,9 @@ class ExampleSpamChecker:
async def check_registration_for_spam(self, email_threepid, username, request_info):
return RegistrationBehaviour.ALLOW # allow all registrations
async def check_media_file_for_spam(self, file_wrapper, file_info):
return False # allow all media
```
## Configuration

47
synapse/events/spamcheck.py
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@ -17,6 +17,8 @@
import inspect
from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple, Union
from synapse.rest.media.v1._base import FileInfo
from synapse.rest.media.v1.media_storage import ReadableFileWrapper
from synapse.spam_checker_api import RegistrationBehaviour
from synapse.types import Collection
from synapse.util.async_helpers import maybe_awaitable
@ -214,3 +216,48 @@ class SpamChecker:
return behaviour
return RegistrationBehaviour.ALLOW
async def check_media_file_for_spam(
self, file_wrapper: ReadableFileWrapper, file_info: FileInfo
) -> bool:
"""Checks if a piece of newly uploaded media should be blocked.
This will be called for local uploads, downloads of remote media, each
thumbnail generated for those, and web pages/images used for URL
previews.
Note that care should be taken to not do blocking IO operations in the
main thread. For example, to get the contents of a file a module
should do::
async def check_media_file_for_spam(
self, file: ReadableFileWrapper, file_info: FileInfo
) -> bool:
buffer = BytesIO()
await file.write_chunks_to(buffer.write)
if buffer.getvalue() == b"Hello World":
return True
return False
Args:
file: An object that allows reading the contents of the media.
file_info: Metadata about the file.
Returns:
True if the media should be blocked or False if it should be
allowed.
"""
for spam_checker in self.spam_checkers:
# For backwards compatibility, only run if the method exists on the
# spam checker
checker = getattr(spam_checker, "check_media_file_for_spam", None)
if checker:
spam = await maybe_awaitable(checker(file_wrapper, file_info))
if spam:
return True
return False

59
synapse/rest/media/v1/media_storage.py
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@ -16,13 +16,17 @@ import contextlib
import logging
import os
import shutil
from typing import IO, TYPE_CHECKING, Any, Optional, Sequence
from typing import IO, TYPE_CHECKING, Any, Callable, Optional, Sequence
import attr
from twisted.internet.defer import Deferred
from twisted.internet.interfaces import IConsumer
from twisted.protocols.basic import FileSender
from synapse.api.errors import NotFoundError
from synapse.logging.context import defer_to_thread, make_deferred_yieldable
from synapse.util import Clock
from synapse.util.file_consumer import BackgroundFileConsumer
from ._base import FileInfo, Responder
@ -58,6 +62,8 @@ class MediaStorage:
self.local_media_directory = local_media_directory
self.filepaths = filepaths
self.storage_providers = storage_providers
self.spam_checker = hs.get_spam_checker()
self.clock = hs.get_clock()
async def store_file(self, source: IO, file_info: FileInfo) -> str:
"""Write `source` to the on disk media store, and also any other
@ -127,18 +133,29 @@ class MediaStorage:
f.flush()
f.close()
spam = await self.spam_checker.check_media_file_for_spam(
ReadableFileWrapper(self.clock, fname), file_info
)
if spam:
logger.info("Blocking media due to spam checker")
# Note that we'll delete the stored media, due to the
# try/except below. The media also won't be stored in
# the DB.
raise SpamMediaException()
for provider in self.storage_providers:
await provider.store_file(path, file_info)
finished_called[0] = True
yield f, fname, finish
except Exception:
except Exception as e:
try:
os.remove(fname)
except Exception:
pass
raise
raise e from None
if not finished_called:
raise Exception("Finished callback not called")
@ -302,3 +319,39 @@ class FileResponder(Responder):
def __exit__(self, exc_type, exc_val, exc_tb):
self.open_file.close()
class SpamMediaException(NotFoundError):
"""The media was blocked by a spam checker, so we simply 404 the request (in
the same way as if it was quarantined).
"""
@attr.s(slots=True)
class ReadableFileWrapper:
"""Wrapper that allows reading a file in chunks, yielding to the reactor,
and writing to a callback.
This is simplified `FileSender` that takes an IO object rather than an
`IConsumer`.
"""
CHUNK_SIZE = 2 ** 14
clock = attr.ib(type=Clock)
path = attr.ib(type=str)
async def write_chunks_to(self, callback: Callable[[bytes], None]):
"""Reads the file in chunks and calls the callback with each chunk.
"""
with open(self.path, "rb") as file:
while True:
chunk = file.read(self.CHUNK_SIZE)
if not chunk:
break
callback(chunk)
# We yield to the reactor by sleeping for 0 seconds.
await self.clock.sleep(0)

12
synapse/rest/media/v1/upload_resource.py
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@ -22,6 +22,7 @@ from twisted.web.http import Request
from synapse.api.errors import Codes, SynapseError
from synapse.http.server import DirectServeJsonResource, respond_with_json
from synapse.http.servlet import parse_string
from synapse.rest.media.v1.media_storage import SpamMediaException
if TYPE_CHECKING:
from synapse.app.homeserver import HomeServer
@ -86,9 +87,14 @@ class UploadResource(DirectServeJsonResource):
# disposition = headers.getRawHeaders(b"Content-Disposition")[0]
# TODO(markjh): parse content-dispostion
content_uri = await self.media_repo.create_content(
media_type, upload_name, request.content, content_length, requester.user
)
try:
content_uri = await self.media_repo.create_content(
media_type, upload_name, request.content, content_length, requester.user
)
except SpamMediaException:
# For uploading of media we want to respond with a 400, instead of
# the default 404, as that would just be confusing.
raise SynapseError(400, "Bad content")
logger.info("Uploaded content with URI %r", content_uri)

94
tests/rest/media/v1/test_media_storage.py
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@ -30,6 +30,8 @@ from twisted.internet import defer
from twisted.internet.defer import Deferred
from synapse.logging.context import make_deferred_yieldable
from synapse.rest import admin
from synapse.rest.client.v1 import login
from synapse.rest.media.v1._base import FileInfo
from synapse.rest.media.v1.filepath import MediaFilePaths
from synapse.rest.media.v1.media_storage import MediaStorage
@ -37,6 +39,7 @@ from synapse.rest.media.v1.storage_provider import FileStorageProviderBackend
from tests import unittest
from tests.server import FakeSite, make_request
from tests.utils import default_config
class MediaStorageTests(unittest.HomeserverTestCase):
@ -398,3 +401,94 @@ class MediaRepoTests(unittest.HomeserverTestCase):
headers.getRawHeaders(b"X-Robots-Tag"),
[b"noindex, nofollow, noarchive, noimageindex"],
)
class TestSpamChecker:
"""A spam checker module that rejects all media that includes the bytes
`evil`.
"""
def __init__(self, config, api):
self.config = config
self.api = api
def parse_config(config):
return config
async def check_event_for_spam(self, foo):
return False # allow all events
async def user_may_invite(self, inviter_userid, invitee_userid, room_id):
return True # allow all invites
async def user_may_create_room(self, userid):
return True # allow all room creations
async def user_may_create_room_alias(self, userid, room_alias):
return True # allow all room aliases
async def user_may_publish_room(self, userid, room_id):
return True # allow publishing of all rooms
async def check_media_file_for_spam(self, file_wrapper, file_info) -> bool:
buf = BytesIO()
await file_wrapper.write_chunks_to(buf.write)
return b"evil" in buf.getvalue()
class SpamCheckerTestCase(unittest.HomeserverTestCase):
servlets = [
login.register_servlets,
admin.register_servlets,
]
def prepare(self, reactor, clock, hs):
self.user = self.register_user("user", "pass")
self.tok = self.login("user", "pass")
# Allow for uploading and downloading to/from the media repo
self.media_repo = hs.get_media_repository_resource()
self.download_resource = self.media_repo.children[b"download"]
self.upload_resource = self.media_repo.children[b"upload"]
def default_config(self):
config = default_config("test")
config.update(
{
"spam_checker": [
{
"module": TestSpamChecker.__module__ + ".TestSpamChecker",
"config": {},
}
]
}
)
return config
def test_upload_innocent(self):
"""Attempt to upload some innocent data that should be allowed.
"""
image_data = unhexlify(
b"89504e470d0a1a0a0000000d4948445200000001000000010806"
b"0000001f15c4890000000a49444154789c63000100000500010d"
b"0a2db40000000049454e44ae426082"
)
self.helper.upload_media(
self.upload_resource, image_data, tok=self.tok, expect_code=200
)
def test_upload_ban(self):
"""Attempt to upload some data that includes bytes "evil", which should
get rejected by the spam checker.
"""
data = b"Some evil data"
self.helper.upload_media(
self.upload_resource, data, tok=self.tok, expect_code=400
)