MeshSate/app/engines/binary.py

"""L2b YARA 规则与二进制分析引擎。

包含：
- YARA 规则匹配（规则库从 ``rules/`` 目录加载，支持热加载）
- PE 文件结构分析（pefile）：节区异常、导入表、编译信息、签名
- 可执行文件能力识别（capa，若已安装）
"""

from __future__ import annotations

import os
import threading
from typing import Any, Dict, List, Optional

from app.engines.base import Engine, EngineResult, Finding, ScanTarget, Severity

BINARY_EXTS = {".exe", ".dll", ".sys", ".scr", ".com", ".cpl", ".ocx", ".msi", ".apk", ".jar", ".so", ".bin", ".elf"}

# ---------- 模块级全局 YARA 规则单例 ----------
# 所有 YaraEngine 实例共享同一个编译结果，避免重复 compile
# rules_dir 不同时（极少见）才分叉加载
_YARA_GLOBAL: Dict[str, Dict[str, Any]] = {}
_YARA_LOCK = threading.Lock()


def _get_global_yara(rules_dir: str) -> Optional[Any]:
    """获取全局共享的 YARA Rules 对象（自动按目录 mtime 重载）。"""
    with _YARA_LOCK:
        cached = _YARA_GLOBAL.get(rules_dir)
        import yara as _yr
        newest = 0.0
        files: List[str] = []
        if os.path.isdir(rules_dir):
            for name in sorted(os.listdir(rules_dir)):
                if name.endswith((".yar", ".yara")):
                    path = os.path.join(rules_dir, name)
                    files.append(path)
                    newest = max(newest, os.path.getmtime(path))

        if cached and cached.get("mtime") == newest:
            return cached.get("rules")

        if not files:
            _YARA_GLOBAL[rules_dir] = {"rules": None, "mtime": newest}
            return None

        try:
            compiled = _yr.compile(filepaths={os.path.basename(p): p for p in files})
        except Exception:
            _YARA_GLOBAL[rules_dir] = {"rules": None, "mtime": newest}
            return None

        _YARA_GLOBAL[rules_dir] = {"rules": compiled, "mtime": newest}
        return compiled


def _discover_rules_dir() -> str:
    """自动探测 YARA 规则目录（优先环境变量 > /app/rules > 项目根 rules/）。"""
    env_dir = os.environ.get("MESHSAFE_RULES_DIR", "").strip()
    if env_dir and os.path.isdir(env_dir):
        return env_dir

    for candidate in ("/app/rules", "rules", "./rules", "../rules"):
        if os.path.isdir(candidate):
            return os.path.abspath(candidate)

    return env_dir or "/app/rules"


class YaraEngine(Engine):
    """YARA 规则匹配引擎（使用全局共享的编译结果）。"""

    name = "yara"
    layer = "L2B"

    def __init__(self, rules_dir: str | None = None) -> None:
        # 显式传入时才用传入值，否则走自动探测
        self.rules_dir = rules_dir if rules_dir else _discover_rules_dir()

    def _load_rules(self) -> Any:
        """委托给全局单例。"""
        try:
            import yara  # noqa: F401 — 只是探测可用性
        except Exception:  # noqa: BLE001
            return None
        return _get_global_yara(self.rules_dir)

    def scan(self, target: ScanTarget, ctx: Any) -> EngineResult:
        result = EngineResult(engine=self.name)
        rules = self._load_rules()
        if rules is None:
            result.ok = False
            result.error = "YARA 规则库不可用或编译失败"
            return result

        try:
            matches = rules.match(target.path)
        except Exception as exc:  # noqa: BLE001
            result.ok = False
            result.error = f"YARA 匹配失败：{exc}"
            return result

        for match in matches:
            severity, weight = _judge_yara_rule(match.rule, match.tags)
            # 覆盖：如果 ctx 里的策略为该 YARA 规则定义了精细权重，用它
            try:
                policy = ctx.policy_engine.policy
                yara_weights = getattr(policy, "yara_weights", {}) or {}
                if match.rule in yara_weights:
                    weight = float(yara_weights[match.rule])
            except Exception:
                pass  # ctx 没有 policy 字段时保持默认 weight
            result.findings.append(
                Finding(
                    engine=self.name,
                    layer=self.layer,
                    severity=severity,
                    rule=match.rule,
                    detail=f"YARA 规则 {match.rule} 命中（标签：{', '.join(match.tags) or '无'}）",
                    weight=weight,
                    meta={"tags": list(match.tags)},
                )
            )
        # rule_set_version 用全局 compiled 对象的 id（每次 reload 变）
        try:
            _r = _get_global_yara(self.rules_dir)
            result.meta["rule_set_version"] = str(id(_r)) if _r else "unavailable"
        except Exception:
            result.meta["rule_set_version"] = "unknown"
        return result

    def health(self) -> Dict[str, Any]:
        rules = self._load_rules()
        ok = rules is not None
        return {
            "engine": self.name,
            "version": "rules" if ok else "none",
            "ok": ok,
            "status": "ok" if ok else "degraded",
            "error": None if ok else "YARA 规则库未加载",
            "info": f"rules_dir={self.rules_dir}" if not ok else "rules loaded",
        }


class BinaryEngine(Engine):
    """PE/二进制文件结构分析引擎。"""

    name = "binary"
    layer = "L2B"

    def scan(self, target: ScanTarget, ctx: Any) -> EngineResult:
        result = EngineResult(engine=self.name)
        ext = (target.declared_ext or "").lower()
        if ext not in BINARY_EXTS:
            return result

        try:
            import pefile
        except Exception:  # noqa: BLE001
            result.ok = False
            result.error = "pefile 未安装"
            return result

        try:
            pe = pefile.PE(target.path, fast_load=False)
        except Exception as exc:  # noqa: BLE001
            result.findings.append(
                Finding(
                    engine=self.name,
                    layer=self.layer,
                    severity=Severity.MEDIUM.value,
                    rule="PeParseFailed",
                    detail=f"PE 结构解析失败：{exc}",
                    weight=10.0,
                )
            )
            return result

        try:
            result.findings.extend(self._analyze(pe, target))
        finally:
            try:
                pe.close()
            except Exception:  # noqa: BLE001
                pass

        return result

    def _analyze(self, pe: Any, target: ScanTarget) -> List[Finding]:
        findings: List[Finding] = []

        # 1) 节区熵值：加密/加壳的节区熵接近 8
        for section in getattr(pe, "sections", []) or []:
            try:
                name = section.Name.rstrip(b"\x00").decode("utf-8", errors="replace")
                entropy = section.get_entropy()
            except Exception:  # noqa: BLE001
                continue
            if entropy >= 7.2:
                findings.append(
                    Finding(
                        engine=self.name,
                        layer=self.layer,
                        severity=Severity.MEDIUM.value,
                        rule="HighEntropySection",
                        detail=f"节区 {name} 熵值 {entropy:.2f}，可能经过加密或加壳",
                        weight=20.0,
                    )
                )

        # 2) 可疑导入表
        suspicious_imports = self._suspicious_imports(pe)
        if suspicious_imports:
            findings.append(
                Finding(
                    engine=self.name,
                    layer=self.layer,
                    severity=Severity.HIGH.value,
                    rule="SuspiciousImports",
                    detail=f"导入表包含高危 API：{', '.join(suspicious_imports[:8])}",
                    weight=45.0,
                )
            )

        # 3) 无签名可执行文件
        if not self._has_signature(pe):
            findings.append(
                Finding(
                    engine=self.name,
                    layer=self.layer,
                    severity=Severity.MEDIUM.value,
                    rule="UnsignedExecutable",
                    detail="可执行文件未携带数字签名",
                    weight=20.0,
                )
            )

        # 4) 编译时间戳异常（明显晚于其他节区时间，或为 1970/未来时间）
        timestamp = getattr(pe, "FILE_HEADER", None)
        if timestamp is not None:
            try:
                ts = int(timestamp.TimeDateStamp)
                if ts == 0 or ts > 4102444800:  # 2100 年之后
                    findings.append(
                        Finding(
                            engine=self.name,
                            layer=self.layer,
                            severity=Severity.LOW.value,
                            rule="SuspiciousTimestamp",
                            detail="PE 编译时间戳异常，可能被伪造",
                            weight=10.0,
                        )
                    )
            except Exception:  # noqa: BLE001
                pass

        # 5) UPX 壳显式检测 —— 检查节名 UPX0 / UPX1 / UPX!
        upx_sections = []
        for section in getattr(pe, "sections", []) or []:
            try:
                name = section.Name.rstrip(b"\x00").decode("utf-8", errors="replace")
                if name.upper().startswith("UPX"):
                    upx_sections.append(name)
            except Exception:
                continue
        if upx_sections:
            findings.append(
                Finding(
                    engine=self.name,
                    layer=self.layer,
                    severity=Severity.MEDIUM.value,
                    rule="UPXPackerDetected",
                    detail=f"检测到 UPX 加壳节：{', '.join(upx_sections)}",
                    weight=30.0,
                )
            )

        # 6) RWX 可写可执行节 —— 高危（绕过 DEP 的典型手法）
        from pefile import SECTION_CHARACTERISTICS  # noqa: PLC0415
        MEM_EXECUTE = SECTION_CHARACTERISTICS["IMAGE_SCN_MEM_EXECUTE"]
        MEM_WRITE = SECTION_CHARACTERISTICS["IMAGE_SCN_MEM_WRITE"]
        rwx_sections = []
        for section in getattr(pe, "sections", []) or []:
            try:
                flags = section.Characteristics
                if (flags & MEM_EXECUTE) and (flags & MEM_WRITE):
                    name = section.Name.rstrip(b"\x00").decode("utf-8", errors="replace")
                    rwx_sections.append(name)
            except Exception:
                continue
        if rwx_sections:
            findings.append(
                Finding(
                    engine=self.name,
                    layer=self.layer,
                    severity=Severity.HIGH.value,
                    rule="RWXSectionDetected",
                    detail=f"检测到可写且可执行的危险节：{', '.join(rwx_sections)}",
                    weight=40.0,
                )
            )

        # 7) 32/64 位识别（info 级别，辅助判断）
        machine = None
        pe32 = None
        try:
            machine = int(pe.FILE_HEADER.Machine)
            pe32 = (pe.OPTIONAL_HEADER.Magic == 0x10B)  # PE32
        except Exception:
            pass
        if machine is not None:
            try:
                from pefile import MACHINE_TYPES  # noqa: PLC0415
                machine_name = MACHINE_TYPES.get(machine, f"UNKNOWN(0x{machine:04x})")
            except Exception:
                machine_name = f"0x{machine:04x}"
            bits = "32-bit" if pe32 else "64-bit"
            findings.append(
                Finding(
                    engine=self.name,
                    layer=self.layer,
                    severity=Severity.LOW.value,
                    rule="PEArchInfo",
                    detail=f"PE 架构：{machine_name} / {bits}",
                    weight=0.0,
                )
            )

        # 8) 调试信息（pdb 路径或 debug 节）
        has_debug_dir = False
        has_debug_section = False
        try:
            debug_dir = pe.OPTIONAL_HEADER.DATA_DIRECTORY[6]  # IMAGE_DIRECTORY_ENTRY_DEBUG
            if debug_dir.VirtualAddress and debug_dir.Size:
                has_debug_dir = True
        except Exception:
            pass
        for section in getattr(pe, "sections", []) or []:
            try:
                name = section.Name.rstrip(b"\x00").decode("utf-8", errors="replace").lower()
                if ".debug" in name or name.startswith("debug") or name.startswith(".pdb"):
                    has_debug_section = True
                    break
            except Exception:
                continue
        if has_debug_dir or has_debug_section:
            findings.append(
                Finding(
                    engine=self.name,
                    layer=self.layer,
                    severity=Severity.LOW.value,
                    rule="DebugInformationPresent",
                    detail="PE 包含调试信息（PDB 路径或 .debug 节），可用于逆向定位",
                    weight=10.0,
                )
            )

        return findings

    def _suspicious_imports(self, pe: Any) -> List[str]:
        """检测高危 API 导入。"""
        suspicious = {
            "VirtualAllocEx", "WriteProcessMemory", "CreateRemoteThread",
            "NtUnmapViewOfSection", "SetWindowsHookEx", "OpenProcess",
            "WinHttpOpen", "InternetOpenUrl", "URLDownloadToFile",
            "CryptEncrypt", "AdjustTokenPrivileges", "CreateService",
            "ShellExecute", "WinExec", "IsDebuggerPresent", "CheckRemoteDebuggerPresent",
        }
        found: List[str] = []
        try:
            for entry in getattr(pe, "DIRECTORY_ENTRY_IMPORT", []) or []:
                for imp in entry.imports:
                    if imp.name:
                        name = imp.name.decode("utf-8", errors="replace")
                        if name in suspicious:
                            found.append(name)
        except Exception:  # noqa: BLE001
            pass
        return sorted(set(found))

    def _has_signature(self, pe: Any) -> bool:
        """检查 PE 是否包含 Authenticode 签名目录。"""
        try:
            directory = pe.OPTIONAL_HEADER.DATA_DIRECTORY[4]  # IMAGE_DIRECTORY_ENTRY_SECURITY
            return bool(directory.VirtualAddress and directory.Size)
        except Exception:  # noqa: BLE001
            return False


def _judge_yara_rule(rule: str, tags: List[str]) -> tuple[str, float]:
    """依据 YARA 规则名与标签判定严重度。"""
    tag_set = {t.lower() for t in tags}
    text = f"{rule} {' '.join(tags)}".lower()

    if "critical" in tag_set or any(k in text for k in ("malware", "ransomware", "backdoor", "c2", "exploit")):
        return Severity.CRITICAL.value, 85.0
    if "high" in tag_set or any(k in text for k in ("trojan", "dropper", "obfusc", "shellcode")):
        return Severity.HIGH.value, 60.0
    if "medium" in tag_set or any(k in text for k in ("suspicious", "pua", "packer")):
        return Severity.MEDIUM.value, 30.0
    if "suspicious" in tag_set:
        return Severity.MEDIUM.value, 30.0
    return Severity.LOW.value, 10.0