fix(cntfilter): allow legacy sensitive-word lists over 64 patterns (#2467)

* fix(cntfilter): allow legacy sensitive-word lists over 64 patterns

Legacy sensitive-words.json files shipped ~70 rules. After v4.10.7,
BanWordFilter treated the 64-pattern safe_regex cap as a hard failure
and blocked every message. Raise the cap only on the sensitive-word
path, keep the 50ms CPU budget, and truncate oversized lists with a
one-time warning.

Fixes #2443

* fix(cntfilter): reject oversized sensitive-word lists

---------

Co-authored-by: dadachann <185672915+dadachann@users.noreply.github.com>

tests/unit_tests/pipeline/test_banwords.py

@@ -0,0 +1,113 @@
+"""BanWordFilter regression tests for legacy sensitive-word lists.
+
+v4.10.7 introduced a 64-pattern cap in safe_regex. Older installs still carry
+the previous default list (~70 patterns). The filter must keep applying those
+rules instead of blocking every message.
+"""
+
+from __future__ import annotations
+
+from importlib import import_module
+from unittest.mock import Mock
+
+import pytest
+
+from tests.factories import FakeApp
+
+
+def _load_banwords():
+    import_module('langbot.pkg.pipeline.pipelinemgr')
+    banwords = import_module('langbot.pkg.pipeline.cntfilter.filters.banwords')
+    entities = import_module('langbot.pkg.pipeline.cntfilter.entities')
+    safe_regex = import_module('langbot.pkg.utils.safe_regex')
+    return banwords, entities, safe_regex
+
+
+def _filter_with_words(words: list[str], *, mask: str = '*', mask_word: str = ''):
+    banwords, entities, _ = _load_banwords()
+    app = FakeApp()
+    app.sensitive_meta = Mock()
+    app.sensitive_meta.data = {
+        'words': words,
+        'mask': mask,
+        'mask_word': mask_word,
+    }
+    return banwords.BanWordFilter(app), entities, app
+
+
+@pytest.mark.asyncio
+async def test_legacy_word_list_over_pattern_cap_does_not_block_clean_message():
+    """A pre-v4.10.7 word list must not fail closed on every message."""
+    _, _, safe_regex = _load_banwords()
+    words = [f'word{i}' for i in range(safe_regex.MAX_PATTERN_COUNT + 6)]
+    filt, entities, _ = _filter_with_words(words)
+
+    result = await filt.process(Mock(), 'hello there, nothing banned')
+
+    assert result.level == entities.ResultLevel.PASS
+    assert result.replacement == 'hello there, nothing banned'
+    assert result.user_notice == ''
+
+
+@pytest.mark.asyncio
+async def test_legacy_word_list_still_masks_match_beyond_first_batch():
+    """Words past the first 64-pattern batch must still be applied."""
+    _, _, safe_regex = _load_banwords()
+    words = [f'word{i}' for i in range(safe_regex.MAX_PATTERN_COUNT)] + ['secret-token']
+    filt, entities, _ = _filter_with_words(words, mask_word='[hidden]')
+
+    result = await filt.process(Mock(), 'please hide secret-token now')
+
+    assert result.level == entities.ResultLevel.MASKED
+    assert 'secret-token' not in result.replacement
+    assert '[hidden]' in result.replacement
+
+
+@pytest.mark.asyncio
+async def test_legacy_word_list_masks_match_in_first_batch():
+    _, _, safe_regex = _load_banwords()
+    words = ['alpha-secret'] + [f'word{i}' for i in range(safe_regex.MAX_PATTERN_COUNT)]
+    filt, entities, _ = _filter_with_words(words, mask_word='[hidden]')
+
+    result = await filt.process(Mock(), 'alpha-secret is here')
+
+    assert result.level == entities.ResultLevel.MASKED
+    assert result.replacement == '[hidden] is here'
+
+
+@pytest.mark.asyncio
+async def test_invalid_sensitive_word_regex_still_blocks():
+    filt, entities, _ = _filter_with_words(['(unclosed'])
+
+    result = await filt.process(Mock(), 'any message')
+
+    assert result.level == entities.ResultLevel.BLOCK
+    assert result.user_notice == '内容检查规则执行失败，请联系管理员'
+    assert 'rejected' in result.console_notice.lower() or 'invalid' in result.console_notice.lower()
+
+
+@pytest.mark.asyncio
+async def test_oversized_word_list_is_blocked():
+    """Configured rules must never be silently skipped when the list is oversized."""
+    banwords, _, _ = _load_banwords()
+    words = [f'word{i}' for i in range(banwords._MAX_SENSITIVE_WORD_PATTERNS + 10)]
+    filt, entities, _ = _filter_with_words(words)
+
+    result = await filt.process(Mock(), 'hello there, nothing banned')
+
+    assert result.level == entities.ResultLevel.BLOCK
+    assert result.replacement == ''
+    assert result.user_notice == '内容检查规则执行失败，请联系管理员'
+    assert 'at most 256 regex patterns are allowed' in result.console_notice.lower()
+
+
+@pytest.mark.asyncio
+async def test_match_beyond_total_cap_cannot_bypass_filter():
+    banwords, _, _ = _load_banwords()
+    words = [f'word{i}' for i in range(banwords._MAX_SENSITIVE_WORD_PATTERNS)] + ['late-secret']
+    filt, entities, _ = _filter_with_words(words, mask_word='[hidden]')
+
+    result = await filt.process(Mock(), 'please hide late-secret now')
+
+    assert result.level == entities.ResultLevel.BLOCK
+    assert result.replacement == ''

tests/unit_tests/utils/test_safe_regex.py

@@ -53,6 +53,45 @@ async def test_matches_any_rejects_pattern_and_input_amplification():
         )
 
 
+@pytest.mark.asyncio
+async def test_mask_patterns_honors_explicit_pattern_count_cap():
+    patterns = ['a'] * (safe_regex.MAX_PATTERN_COUNT + 6)
+    found, masked = await safe_regex.mask_patterns(
+        patterns,
+        'hello',
+        mask='*',
+        mask_word='',
+        max_pattern_count=len(patterns),
+    )
+    assert found is False
+    assert masked == 'hello'
+
+    with pytest.raises(safe_regex.SafeRegexLimitError):
+        await safe_regex.mask_patterns(
+            patterns,
+            'hello',
+            mask='*',
+            mask_word='',
+        )
+
+
+@pytest.mark.asyncio
+async def test_mask_patterns_rejects_oversized_sequence_before_copying_it():
+    class OversizedPatterns(list):
+        def __iter__(self):
+            raise AssertionError('oversized patterns must not be materialized')
+
+    patterns = OversizedPatterns(['a'] * (safe_regex.MAX_PATTERN_COUNT + 1))
+
+    with pytest.raises(safe_regex.SafeRegexLimitError):
+        await safe_regex.mask_patterns(
+            patterns,
+            'hello',
+            mask='*',
+            mask_word='',
+        )
+
+
 @pytest.mark.asyncio
 async def test_mask_patterns_bounds_replacement_growth_and_masks_matches():
     found, masked = await safe_regex.mask_patterns(