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Properly parse event_fields in filters (#15607) 

The event_fields property in filters should use the proper
escape rules, namely backslashes can be escaped with
an additional backslash.

This adds tests (adapted from matrix-js-sdk) and implements
the logic to properly split the event_fields strings.
This commit is contained in:
Patrick Cloke 2023-05-22 11:31:22 -04:00 committed by GitHub
parent 201597fc86
commit c5d1e6d414
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5 changed files with 99 additions and 34 deletions
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1
changelog.d/15607.bugfix Normal file
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@ -0,0 +1 @@
Fix a long-standing bug where filters with multiple backslashes were rejected.

15
synapse/api/filtering.py
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@ -128,20 +128,7 @@ USER_FILTER_SCHEMA = {
"account_data": {"$ref": "#/definitions/filter"},
"room": {"$ref": "#/definitions/room_filter"},
"event_format": {"type": "string", "enum": ["client", "federation"]},
"event_fields": {
"type": "array",
"items": {
"type": "string",
# Don't allow '\\' in event field filters. This makes matching
# events a lot easier as we can then use a negative lookbehind
# assertion to split '\.' If we allowed \\ then it would
# incorrectly split '\\.' See synapse.events.utils.serialize_event
#
# Note that because this is a regular expression, we have to escape
# each backslash in the pattern.
"pattern": r"^((?!\\\\).)*$",
},
},
"event_fields": {"type": "array", "items": {"type": "string"}},
},
"additionalProperties": True, # Allow new fields for forward compatibility
}

72
synapse/events/utils.py
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@ -22,6 +22,7 @@ from typing import (
Iterable,
List,
Mapping,
Match,
MutableMapping,
Optional,
Union,
@ -46,12 +47,10 @@ if TYPE_CHECKING:
from synapse.handlers.relations import BundledAggregations
# Split strings on "." but not "\." This uses a negative lookbehind assertion for '\'
# (?<!stuff) matches if the current position in the string is not preceded
# by a match for 'stuff'.
# TODO: This is fast, but fails to handle "foo\\.bar" which should be treated as
# the literal fields "foo\" and "bar" but will instead be treated as "foo\\.bar"
SPLIT_FIELD_REGEX = re.compile(r"(?<!\\)\.")
# Split strings on "." but not "\." (or "\\\.").
SPLIT_FIELD_REGEX = re.compile(r"\\*\.")
# Find escaped characters, e.g. those with a \ in front of them.
ESCAPE_SEQUENCE_PATTERN = re.compile(r"\\(.)")
CANONICALJSON_MAX_INT = (2**53) - 1
CANONICALJSON_MIN_INT = -CANONICALJSON_MAX_INT
@ -253,6 +252,57 @@ def _copy_field(src: JsonDict, dst: JsonDict, field: List[str]) -> None:
sub_out_dict[key_to_move] = sub_dict[key_to_move]
def _escape_slash(m: Match[str]) -> str:
"""
Replacement function; replace a backslash-backslash or backslash-dot with the
second character. Leaves any other string alone.
"""
if m.group(1) in ("\\", "."):
return m.group(1)
return m.group(0)
def _split_field(field: str) -> List[str]:
"""
Splits strings on unescaped dots and removes escaping.
Args:
field: A string representing a path to a field.
Returns:
A list of nested fields to traverse.
"""
# Convert the field and remove escaping:
#
# 1. "content.body.thing\.with\.dots"
# 2. ["content", "body", "thing\.with\.dots"]
# 3. ["content", "body", "thing.with.dots"]
# Find all dots (and their preceding backslashes). If the dot is unescaped
# then emit a new field part.
result = []
prev_start = 0
for match in SPLIT_FIELD_REGEX.finditer(field):
# If the match is an *even* number of characters than the dot was escaped.
if len(match.group()) % 2 == 0:
continue
# Add a new part (up to the dot, exclusive) after escaping.
result.append(
ESCAPE_SEQUENCE_PATTERN.sub(
_escape_slash, field[prev_start : match.end() - 1]
)
)
prev_start = match.end()
# Add any part of the field after the last unescaped dot. (Note that if the
# character is a dot this correctly adds a blank string.)
result.append(re.sub(r"\\(.)", _escape_slash, field[prev_start:]))
return result
def only_fields(dictionary: JsonDict, fields: List[str]) -> JsonDict:
"""Return a new dict with only the fields in 'dictionary' which are present
in 'fields'.
@ -260,7 +310,7 @@ def only_fields(dictionary: JsonDict, fields: List[str]) -> JsonDict:
If there are no event fields specified then all fields are included.
The entries may include '.' characters to indicate sub-fields.
So ['content.body'] will include the 'body' field of the 'content' object.
A literal '.' character in a field name may be escaped using a '\'.
A literal '.' or '\' character in a field name may be escaped using a '\'.
Args:
dictionary: The dictionary to read from.
@ -275,13 +325,7 @@ def only_fields(dictionary: JsonDict, fields: List[str]) -> JsonDict:
# for each field, convert it:
# ["content.body.thing\.with\.dots"] => [["content", "body", "thing\.with\.dots"]]
split_fields = [SPLIT_FIELD_REGEX.split(f) for f in fields]
# for each element of the output array of arrays:
# remove escaping so we can use the right key names.
split_fields[:] = [
[f.replace(r"\.", r".") for f in field_array] for field_array in split_fields
]
split_fields = [_split_field(f) for f in fields]
output: JsonDict = {}
for field_array in split_fields:

6
tests/api/test_filtering.py
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@ -48,8 +48,6 @@ class FilteringTestCase(unittest.HomeserverTestCase):
invalid_filters: List[JsonDict] = [
# `account_data` must be a dictionary
{"account_data": "Hello World"},
# `event_fields` entries must not contain backslashes
{"event_fields": [r"\\foo"]},
# `event_format` must be "client" or "federation"
{"event_format": "other"},
# `not_rooms` must contain valid room IDs
@ -114,10 +112,6 @@ class FilteringTestCase(unittest.HomeserverTestCase):
"event_format": "client",
"event_fields": ["type", "content", "sender"],
},
# a single backslash should be permitted (though it is debatable whether
# it should be permitted before anything other than `.`, and what that
# actually means)
#
# (note that event_fields is implemented in
# synapse.events.utils.serialize_event, and so whether this actually works
# is tested elsewhere. We just want to check that it is allowed through the

39
tests/events/test_utils.py
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@ -16,6 +16,7 @@ import unittest as stdlib_unittest
from typing import Any, List, Mapping, Optional
import attr
from parameterized import parameterized
from synapse.api.constants import EventContentFields
from synapse.api.room_versions import RoomVersions
@ -23,6 +24,7 @@ from synapse.events import EventBase, make_event_from_dict
from synapse.events.utils import (
PowerLevelsContent,
SerializeEventConfig,
_split_field,
copy_and_fixup_power_levels_contents,
maybe_upsert_event_field,
prune_event,
@ -794,3 +796,40 @@ class CopyPowerLevelsContentTestCase(stdlib_unittest.TestCase):
def test_invalid_nesting_raises_type_error(self) -> None:
with self.assertRaises(TypeError):
copy_and_fixup_power_levels_contents({"a": {"b": {"c": 1}}}) # type: ignore[dict-item]
class SplitFieldTestCase(stdlib_unittest.TestCase):
@parameterized.expand(
[
# A field with no dots.
["m", ["m"]],
# Simple dotted fields.
["m.foo", ["m", "foo"]],
["m.foo.bar", ["m", "foo", "bar"]],
# Backslash is used as an escape character.
[r"m\.foo", ["m.foo"]],
[r"m\\.foo", ["m\\", "foo"]],
[r"m\\\.foo", [r"m\.foo"]],
[r"m\\\\.foo", ["m\\\\", "foo"]],
[r"m\foo", [r"m\foo"]],
[r"m\\foo", [r"m\foo"]],
[r"m\\\foo", [r"m\\foo"]],
[r"m\\\\foo", [r"m\\foo"]],
# Ensure that escapes at the end don't cause issues.
["m.foo\\", ["m", "foo\\"]],
["m.foo\\", ["m", "foo\\"]],
[r"m.foo\.", ["m", "foo."]],
[r"m.foo\\.", ["m", "foo\\", ""]],
[r"m.foo\\\.", ["m", r"foo\."]],
# Empty parts (corresponding to properties which are an empty string) are allowed.
[".m", ["", "m"]],
["..m", ["", "", "m"]],
["m.", ["m", ""]],
["m..", ["m", "", ""]],
["m..foo", ["m", "", "foo"]],
# Invalid escape sequences.
[r"\m", [r"\m"]],
]
)
def test_split_field(self, input: str, expected: str) -> None:
self.assertEqual(_split_field(input), expected)