feat(ttp): E.3.7 RuleEngine — evaluate + atomic-swap watch_store
Implements the rule engine body left empty at contract phase: evaluate() dispatches by source_kind through self._by_kind, runs the rule's match spec against event.payload, and emits one TTPTag per emits entry. watch_store() loads the initial corpus from RuleStore.load_compiled, then drains subscribe_changes, applying definition changes via single-statement dict assignment (atomic swap, GIL-atomic to readers) and state changes via NamedTuple._replace on the existing CompiledRule. Why: with the FS + DB stores in place (E.3.5/E.3.6), the engine is the last piece of the rule plane. Lifters (E.3.9–E.3.13) consume the engine; the worker bootstrap (E.3.14) wires watch_store into the asyncio event loop. After this commit a CompositeTagger constructed with a RuleEngine + a populated rules dir will produce real tags. Notes: - CompiledRule.emits extended to 4-tuple (technique_id, sub_technique_id, tactic, confidence). Tactic + confidence ride per-emit so a single rule can carry multiple precision targets (the "one event maps to many techniques" property). Compile helpers in both backends extract them from the YAML emits dict; missing tactic or confidence is a deploy-time error. - v0 match operator is "pattern" (regex). The field defaults per source_kind (command_text / raw_url / subject / verdict / …) and is overridable via match.field. Future ops (contains, equals, in_set) extend _match_event without touching the engine surface. - Confidence model: rules with state="clipped" + confidence_max set cap the per-emit confidence downward; clipped is a soft suppress, not a hard skip. Disabled rules are skipped wholly; expires_at past is re-checked at evaluate as defense-in-depth (the store auto-reverts, but a racing read between expiry and revert must not fire the rule). - _span(name, **attrs) helper in engine + both stores short-circuits on decnet.telemetry._ENABLED — matches the project's @traced / wrap_repository zero-overhead-when-disabled pattern instead of relying solely on the no-op tracer indirection. - Late-bound tracer (telemetry.get_tracer called per-span, not at module load) so test_tracing's monkeypatch reaches the production code path. xfails flipped: tests/ttp/test_rule_engine.py multi-emit fan-out + rule_version-collision-via-engine; tests/ttp/test_multi_mapping.py N×M engine fan-out + idempotent replay; tests/ttp/test_tracing.py ttp.eval span hierarchy + ttp.rule.fire span attributes. Tests: 214 passed, 19 xfailed (gated on E.3.8 lifters / rule pack / worker bootstrap). mypy: clean on prod code; pre-existing test-stub arg-type warnings unchanged.
This commit is contained in:
@@ -27,12 +27,17 @@ file is importable before that step lands.
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"""
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from __future__ import annotations
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import re
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from collections.abc import Iterator
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from contextlib import contextmanager
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from typing import TYPE_CHECKING, Any, NamedTuple
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from pydantic import BaseModel, Field
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from decnet import telemetry as _telemetry
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from decnet.logging import get_logger
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from decnet.ttp.base import TaggerEvent
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from decnet.web.db.models.ttp import TTPTag
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from decnet.web.db.models.ttp import TTPTag, compute_tag_uuid
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if TYPE_CHECKING:
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# Store contracts ship in E.1.11. Forward-referenced under
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@@ -40,7 +45,42 @@ if TYPE_CHECKING:
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# without creating a circular shape dependency on a not-yet-shipped
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# subpackage. Concrete construction happens at the worker layer
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# (E.1.7) where both halves are in scope.
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from decnet.ttp.store.base import RuleState, RuleStore
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from decnet.ttp.store.base import RuleChange, RuleState, RuleStore
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_log = get_logger("ttp.engine")
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@contextmanager
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def _span(name: str, **attrs: Any) -> Iterator[Any]:
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"""Span context manager gated on ``DECNET_DEVELOPER_TRACING``.
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Same shape as the helpers in :mod:`decnet.ttp.store.impl.filesystem`
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/ :mod:`decnet.ttp.store.impl.database`: zero per-call overhead when
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tracing is off (single attribute lookup, then yield ``None``);
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late-bound tracer when on so the test_tracing monkeypatch reaches
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us. Modeled on the project's ``@traced`` / ``wrap_repository``
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no-overhead-when-disabled pattern.
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"""
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if not _telemetry._ENABLED:
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yield None
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return
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tracer = _telemetry.get_tracer("ttp.engine")
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with tracer.start_as_current_span(name) as span:
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for key, value in attrs.items():
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try:
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span.set_attribute(key, value)
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except (TypeError, ValueError):
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continue
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yield span
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# ATT&CK release stamped on every emitted tag. Pinned at the engine
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# layer rather than per-rule because rule authors don't manage ATT&CK
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# matrix drift; the engine owns that. Bumping this value invalidates
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# tag UUID continuity across deploys, so the bump must land alongside a
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# documented ATT&CK upgrade per TTP_TAGGING.md §"Hard parts §8".
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_ATTACK_RELEASE: str = "v15.1"
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class CompiledRule(NamedTuple):
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@@ -71,9 +111,11 @@ class CompiledRule(NamedTuple):
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#: phase (E.3). Kept ``dict[str, Any]`` here rather than typed so
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#: rule authors can extend match operators without touching the ABC.
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match_spec: dict[str, Any]
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#: ``((technique_id, sub_technique_id | None), ...)``. Tuple, not
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#: list, so the record stays hashable.
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emits: tuple[tuple[str, str | None], ...]
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#: ``((technique_id, sub_technique_id | None, tactic, confidence), ...)``
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#: per emit. Tuple-of-tuples, not list, so the record stays hashable.
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#: One YAML rule may emit N tags from a single match — see
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#: TTP_TAGGING.md §"One event maps to many techniques".
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emits: tuple[tuple[str, str | None, str, float], ...]
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#: Names of evidence keys the rule populates on emitted tags.
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evidence_fields: tuple[str, ...]
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#: Operational state stamped in by the store at compile time.
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@@ -95,7 +137,13 @@ class RuleSchema(BaseModel):
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name: str
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applies_to: list[str]
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match: dict[str, Any]
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emits: list[dict[str, str]]
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#: ``[{"tactic": "TA0007", "technique_id": "T1083",
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#: "sub_technique_id": "T1083.001"?, "confidence": 0.85}, ...]``
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#: Per-emit tactic + confidence ride here so a single rule can carry
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#: multiple precision targets (the "one event maps to many techniques"
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#: case from TTP_TAGGING.md, including different confidences per
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#: technique on the same match).
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emits: list[dict[str, Any]]
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evidence_fields: list[str] = Field(default_factory=list)
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@@ -116,30 +164,245 @@ class RuleEngine:
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def __init__(self, store: "RuleStore") -> None:
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self._store = store
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# ``source_kind`` → list of compiled rules that claim it.
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# Empty here; populated by :meth:`watch_store` once the store
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# contract lands (E.1.11).
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# Replaced wholesale on per-rule changes via watch_store(); the
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# GIL-atomic dict assignment is the "atomic swap" pin from
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# TTP_TAGGING.md §"Atomic swap" / E.2.14b.
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self._by_kind: dict[str, list[CompiledRule]] = {}
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# Mirror keyed by rule_id for definition+state restamping.
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# Same atomicity contract: replacement, never in-place mutation.
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self._by_rule: dict[str, CompiledRule] = {}
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async def evaluate(self, event: TaggerEvent) -> list[TTPTag]:
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"""Return zero or more tags produced by rules matching *event*.
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Empty in the contract phase. The impl phase fans the event out
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to ``self._by_kind[event.source_kind]`` and merges results.
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Dispatches by ``event.source_kind``; for each rule whose
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``applies_to`` set covers the kind, runs the match spec against
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``event.payload`` and emits one :class:`TTPTag` per ``emits``
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entry. Confidence is the per-emit base scaled by the rule's
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:class:`RuleState.confidence_max` ceiling (no-op when ``None``).
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Disabled rules are skipped; the store auto-reverts expired
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states, but the engine double-checks ``expires_at`` as
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defense-in-depth.
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"""
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return []
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rules = self._by_kind.get(event.source_kind, [])
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if not rules:
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return []
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with _span(
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"ttp.eval",
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attacker_uuid=str(event.attacker_uuid or ""),
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identity_uuid=str(event.identity_uuid or ""),
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source_kind=event.source_kind,
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):
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return _evaluate_rules(rules, event)
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async def watch_store(self) -> None:
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"""Subscribe to per-rule changes and atomically swap them in.
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Reads from :meth:`RuleStore.subscribe_changes`. Each yielded
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change is one rule_id; the engine recompiles that rule alone
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and replaces the corresponding entries in the dispatch index
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in a single assignment. Never returns under normal operation —
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the worker cancels it during shutdown.
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Empty in the contract phase.
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Loads the initial corpus from :meth:`RuleStore.load_compiled`,
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builds the dispatch index, then drains
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:meth:`RuleStore.subscribe_changes` forever. Each ``definition``
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change replaces the affected rule wholesale; each ``state``
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change re-stamps the existing :class:`CompiledRule`'s ``state``
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field via NamedTuple ``_replace`` (single dict assignment, no
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in-place mutation).
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"""
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return None
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# Forward import — avoids the contract-phase circular shape
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# dependency captured by the TYPE_CHECKING block above.
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from decnet.ttp.store.base import RuleState # noqa: PLC0415
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compiled = await self._store.load_compiled()
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for rule in compiled:
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self._install(rule)
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async for change in self._store.subscribe_changes():
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try:
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self._apply_change(change, RuleState)
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except Exception: # noqa: BLE001
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_log.exception(
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"ttp.engine: rule change apply failed rule_id=%s",
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change.rule_id,
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)
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# ── Internals ───────────────────────────────────────────────────
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def _install(self, rule: CompiledRule) -> None:
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"""Atomic-swap install of one compiled rule.
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Empty ``applies_to`` + empty ``emits`` is the deletion sentinel
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used by both backends — drop the rule from the index instead of
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adding a no-op entry.
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"""
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if not rule.applies_to and not rule.emits:
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self._evict(rule.rule_id)
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return
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self._by_rule[rule.rule_id] = rule
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for kind in rule.applies_to:
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current = self._by_kind.get(kind, [])
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replaced = [r for r in current if r.rule_id != rule.rule_id]
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replaced.append(rule)
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# Single dict assignment — GIL-atomic to readers.
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self._by_kind[kind] = replaced
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def _evict(self, rule_id: str) -> None:
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existing = self._by_rule.pop(rule_id, None)
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if existing is None:
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return
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for kind in existing.applies_to:
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current = self._by_kind.get(kind, [])
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replaced = [r for r in current if r.rule_id != rule_id]
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self._by_kind[kind] = replaced
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def _apply_change(
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self, change: "RuleChange", state_cls: type,
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) -> None:
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if change.change_kind == "definition":
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value = change.new_value
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if isinstance(value, CompiledRule):
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self._install(value)
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return
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# state change
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existing = self._by_rule.get(change.rule_id)
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if existing is None or not isinstance(change.new_value, state_cls):
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return
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new_state = change.new_value # narrowed by isinstance above
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# NamedTuple._replace returns a fresh frozen tuple — single
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# dict assignment swaps it in atomically.
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restamped = existing._replace(state=new_state) # type: ignore[arg-type]
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self._by_rule[change.rule_id] = restamped
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for kind in restamped.applies_to:
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current = self._by_kind.get(kind, [])
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replaced = [r for r in current if r.rule_id != change.rule_id]
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replaced.append(restamped)
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self._by_kind[kind] = replaced
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def _state_active(state: "RuleState") -> bool:
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"""A rule fires iff its state isn't ``disabled``. ``clipped`` rules
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still fire — the clip caps confidence, doesn't suppress.
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"""
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if state.state == "disabled":
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return False
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if state.expires_at is not None:
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# Defense-in-depth: stores auto-revert expired states, but a
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# racing read between expiry and revert must not fire a rule
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# the operator told us was off.
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from datetime import datetime, timezone # noqa: PLC0415
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expires = state.expires_at
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if expires.tzinfo is None:
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expires = expires.replace(tzinfo=timezone.utc)
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if expires < datetime.now(tz=timezone.utc):
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return False
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return True
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def _match_event(rule: CompiledRule, event: TaggerEvent) -> bool:
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"""Run the rule's match spec against ``event.payload``.
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For v0 the only operator is ``pattern`` — a regex against a
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payload field. The field name comes from ``match_spec["field"]``
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if present, otherwise the per-source-kind default
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(``command_text`` for ``command``, ``raw_url`` for
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``http_request``, etc.). A future PR can extend this to
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``contains``, ``equals``, ``in_set`` without touching the engine
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surface — only this function changes.
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"""
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spec = rule.match_spec
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pattern = spec.get("pattern")
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if pattern is None:
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return False
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field = spec.get("field") or _default_field(event.source_kind)
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if field is None:
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return False
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haystack = event.payload.get(field)
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if not isinstance(haystack, str):
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return False
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try:
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return re.search(pattern, haystack) is not None
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except re.error:
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# Malformed regex made it past schema validation — log and
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# don't fire. The deploy-time hook (load_compiled) catches
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# most of these; this path is the runtime fallback.
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_log.warning(
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"ttp.engine: bad regex in rule %s: %r", rule.rule_id, pattern,
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)
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return False
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def _default_field(source_kind: str) -> str | None:
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return _DEFAULT_MATCH_FIELD.get(source_kind)
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# Per-source_kind default field for the ``pattern`` operator. New
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# source_kinds can override via ``match.field`` in the YAML rule.
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_DEFAULT_MATCH_FIELD: dict[str, str] = {
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"command": "command_text",
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"http_request": "raw_url",
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"email": "subject",
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"intel": "verdict",
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"canary_fingerprint": "ua_signature",
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"auth_attempt": "username",
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"payload": "payload_text",
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}
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def _evaluate_rules(
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rules: list[CompiledRule], event: TaggerEvent,
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) -> list[TTPTag]:
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out: list[TTPTag] = []
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for rule in rules:
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if not _state_active(rule.state):
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continue
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if not _match_event(rule, event):
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continue
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ceiling = (
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rule.state.confidence_max
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if rule.state.state == "clipped"
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and rule.state.confidence_max is not None
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else 1.0
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)
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with _span(
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"ttp.rule.fire",
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rule_id=rule.rule_id,
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rule_version=rule.rule_version,
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) as span:
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for technique_id, sub_technique_id, tactic, base_conf in rule.emits:
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if span is not None:
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try:
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span.set_attribute("technique_id", technique_id)
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except (TypeError, ValueError):
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pass
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confidence = min(base_conf, base_conf * ceiling) if ceiling < 1.0 else base_conf
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tag_uuid = compute_tag_uuid(
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source_kind=event.source_kind,
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source_id=event.source_id,
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rule_id=rule.rule_id,
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rule_version=rule.rule_version,
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technique_id=technique_id,
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sub_technique_id=sub_technique_id,
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)
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evidence: dict[str, Any] = {
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field: event.payload.get(field)
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for field in rule.evidence_fields
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if field in event.payload
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}
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out.append(TTPTag(
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uuid=tag_uuid,
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source_kind=event.source_kind,
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source_id=event.source_id,
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attacker_uuid=event.attacker_uuid,
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identity_uuid=event.identity_uuid,
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session_id=event.session_id,
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decky_id=event.decky_id,
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tactic=tactic,
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technique_id=technique_id,
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sub_technique_id=sub_technique_id,
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confidence=confidence,
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rule_id=rule.rule_id,
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rule_version=rule.rule_version,
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evidence=evidence,
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attack_release=_ATTACK_RELEASE,
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))
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return out
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__all__ = [
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Reference in New Issue
Block a user