fix(exporting): F01 路径完整验证前不登记清理目标，清理不跟随符号链接

- 根目录/用户目录/目标文件先通过 lstat 完整校验（拒绝符号链接与非目录），
  校验失败时不删除任何磁盘文件（此前父目录为链接时会沿链接 unlink 同名文件）
- 失败清理只处理本次登记的受控文件，并通过 O_NOFOLLOW 目录描述符删除；
  目录被换成符号链接时拒绝删除，保留任务编号与路径的对应关系
- 测试覆盖：用户目录链接、目标链接、运行中目录被换成链接（受保护文件字节不变）、
  失败后正常重试成功

finance/exporting.py

@@ -1,7 +1,9 @@
 import hashlib
 import hmac
+import logging
 import os
 import secrets
+import stat
 import warnings
 from datetime import timedelta
 from decimal import Decimal, InvalidOperation
@@ -28,6 +30,58 @@ FORMULA_VERSION = "3"
 MAX_ROWS = 100_000
 MAX_GROUPS = 200
 
+logger = logging.getLogger(__name__)
+
+
+def _validated_export_directory(path, description):
+    """导出目录必须不存在或为真实目录；符号链接一律拒绝并保持文件原样。"""
+    try:
+        info = os.lstat(path)
+    except FileNotFoundError:
+        path.mkdir(parents=True, mode=0o700)
+        info = os.lstat(path)
+    if stat.S_ISLNK(info.st_mode) or not stat.S_ISDIR(info.st_mode):
+        raise ValueError(f"{description}必须是真实目录，不能是符号链接")
+    os.chmod(path, 0o700)
+    return path
+
+
+def _validated_export_target(user_dir, job):
+    """目标文件若已存在必须是普通文件；符号链接或其他类型一律拒绝覆盖。"""
+    target = user_dir / f"{job.pk}.xlsx"
+    try:
+        info = os.lstat(target)
+    except FileNotFoundError:
+        return target
+    if stat.S_ISLNK(info.st_mode) or not stat.S_ISREG(info.st_mode):
+        raise ValueError("公式导出目标路径已存在且不是普通文件，已拒绝生成")
+    return target
+
+
+def _unlink_created_file(path):
+    """只通过不跟随链接的目录句柄删除受控目录内的普通文件。
+
+    返回 "removed"（已删除）、"missing"（本就不存在）或 "blocked"（无法安全删除，
+    例如目录已被换成符号链接或权限不足），调用方据此保留失败任务与磁盘的一致性。
+    """
+    try:
+        dir_fd = os.open(path.parent, os.O_RDONLY | os.O_NOFOLLOW)
+    except OSError:
+        return "blocked"
+    try:
+        try:
+            info = os.lstat(path.name, dir_fd=dir_fd)
+        except FileNotFoundError:
+            return "missing"
+        if not stat.S_ISREG(info.st_mode):
+            return "blocked"
+        os.unlink(path.name, dir_fd=dir_fd)
+        return "removed"
+    except OSError:
+        return "blocked"
+    finally:
+        os.close(dir_fd)
+
 
 def _excel_number(value):
     if value is None:
@@ -594,41 +648,34 @@ def build_formula_workbook(ds, member, export_context, output):
 
 def process_formula_export(export_id):
     job = FormulaExport.objects.select_related("dataset", "user").get(pk=export_id)
-    temporary = None
     target = None
+    created = []
     try:
-        root = Path(settings.MEDIA_ROOT) / "formula-exports"
-        if root.is_symlink():
-            raise ValueError("公式导出目录不能是符号链接")
-        root.mkdir(parents=True, exist_ok=True, mode=0o700)
-        root.chmod(0o700)
-        target = root / str(job.user_id) / f"{job.pk}.xlsx"
-        target.parent.mkdir(parents=True, exist_ok=True, mode=0o700)
-        if target.parent.is_symlink() or target.is_symlink():
-            raise ValueError("公式导出路径不能是符号链接")
-        target.parent.chmod(0o700)
-        temporary = target.with_name(f"{job.pk}.{secrets.token_hex(8)}.tmp")
         member = Membership.objects.get(user=job.user, organization=job.dataset.organization)
         if set(member.departments) != set(job.departments):
             raise PermissionError("科室授权已变更，请重新提交导出")
+        root = _validated_export_directory(Path(settings.MEDIA_ROOT) / "formula-exports", "公式导出目录")
+        user_dir = _validated_export_directory(root / str(job.user_id), "公式导出用户目录")
+        target = _validated_export_target(user_dir, job)
+        # 路径完整验证通过后才把目标登记为可清理文件；此前任何失败都不会删除磁盘文件。
+        created.append(target)
+        temporary = target.with_name(f"{job.pk}.{secrets.token_hex(8)}.tmp")
         descriptor = os.open(temporary, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600)
+        created.append(temporary)
         with os.fdopen(descriptor, "wb") as file:
             stats = build_formula_workbook(job.dataset, member, job.context, file)
-        temporary.replace(target)
+        os.replace(temporary, target)
+        created = [target]
         job.path, job.status, job.error = str(target), "succeeded", ""
         job.finished_at = timezone.now()
         job.expires_at = timezone.now() + timedelta(hours=24)
         job.save(update_fields=["path", "status", "error", "finished_at", "expires_at"])
         return stats
     except Exception as exc:
-        for path in (temporary, target):
+        job.status, job.error, job.finished_at, job.expires_at = "failed", str(exc)[:500], timezone.now(), None
-            try:
+        # 只清理本次登记且确认位于受控目录内的文件；目录被换成符号链接时拒绝删除。
-                if path is not None and not path.is_symlink():
+        leftover = [path for path in created if _unlink_created_file(path) == "blocked"]
-                    path.unlink(missing_ok=True)
+        job.path = str(target) if target in leftover else ""
-            except OSError:
-                pass
-        job.status, job.error, job.path = "failed", str(exc)[:500], ""
-        job.finished_at, job.expires_at = timezone.now(), None
         job.save(update_fields=["status", "error", "path", "finished_at", "expires_at"])
         raise
 

tests/test_formula_export_reliability.py

@@ -198,6 +198,114 @@ def test_formula_export_worker_records_path_preparation_failure(workspace, setti
     assert job.status == "failed"
 
 
+def _queued_job(ds):
+    return FormulaExport.objects.create(
+        dataset=ds,
+        user=ds.created_by,
+        context={"start": "2026-08", "end": "2026-08", "comparison": "yoy", "group": "department"},
+    )
+
+
+def test_failed_export_rejects_symlinked_user_directory_without_touching_files(workspace, settings):
+    from finance.exporting import process_formula_export
+
+    ds, *_ = workspace
+    job = _queued_job(ds)
+    root = Path(settings.MEDIA_ROOT) / "formula-exports"
+    root.mkdir(parents=True)
+    protected = Path(settings.MEDIA_ROOT) / "protected"
+    protected.mkdir()
+    victim = protected / f"{job.pk}.xlsx"
+    victim.write_bytes(b"protected workbook")
+    (root / str(job.user_id)).symlink_to(protected, target_is_directory=True)
+
+    with pytest.raises(ValueError, match="符号链接"):
+        process_formula_export(job.pk)
+
+    job.refresh_from_db()
+    assert job.status == "failed"
+    assert not job.path
+    assert victim.read_bytes() == b"protected workbook"
+    assert list(protected.glob("*.tmp")) == []
+
+
+def test_failed_export_rejects_symlinked_target_and_keeps_link(workspace, settings):
+    from finance.exporting import process_formula_export
+
+    ds, *_ = workspace
+    job = _queued_job(ds)
+    user_dir = Path(settings.MEDIA_ROOT) / "formula-exports" / str(job.user_id)
+    user_dir.mkdir(parents=True)
+    protected_file = Path(settings.MEDIA_ROOT) / "protected.xlsx"
+    protected_file.write_bytes(b"protected workbook")
+    (user_dir / f"{job.pk}.xlsx").symlink_to(protected_file)
+
+    with pytest.raises(ValueError, match="普通文件"):
+        process_formula_export(job.pk)
+
+    job.refresh_from_db()
+    assert job.status == "failed"
+    assert protected_file.read_bytes() == b"protected workbook"
+    assert (user_dir / f"{job.pk}.xlsx").is_symlink()
+    assert list(user_dir.glob("*.tmp")) == []
+
+
+def test_failed_export_refuses_cleanup_when_parent_directory_swapped_to_symlink(
+    workspace, settings, monkeypatch
+):
+    from finance.exporting import process_formula_export
+
+    ds, *_ = workspace
+    job = _queued_job(ds)
+    root = Path(settings.MEDIA_ROOT) / "formula-exports"
+    user_dir = root / str(job.user_id)
+    user_dir.mkdir(parents=True)
+    protected = Path(settings.MEDIA_ROOT) / "protected"
+    protected.mkdir()
+    victim = protected / f"{job.pk}.xlsx"
+    victim.write_bytes(b"protected workbook")
+
+    def swap_and_fail(*args, **kwargs):
+        args[-1].write(b"partial")
+        user_dir.rename(user_dir.with_name("swapped"))
+        user_dir.symlink_to(protected, target_is_directory=True)
+        raise ValueError("controlled failure after path validation")
+
+    monkeypatch.setattr("finance.exporting.build_formula_workbook", swap_and_fail)
+    with pytest.raises(ValueError, match="controlled failure"):
+        process_formula_export(job.pk)
+
+    job.refresh_from_db()
+    assert job.status == "failed"
+    assert victim.read_bytes() == b"protected workbook"
+    assert user_dir.is_symlink()
+    # 本次创建的临时文件残留在被换名的原目录中，由清理命令按保留期回收。
+    assert list((root / "swapped").glob(f"{job.pk}.*.tmp"))
+
+
+def test_formula_export_retry_after_failure_succeeds(workspace, monkeypatch):
+    from finance.exporting import process_formula_export
+
+    ds, *_ = workspace
+    job = _queued_job(ds)
+
+    def fail(*args, **kwargs):
+        args[-1].write(b"partial")
+        raise ValueError("controlled export failure")
+
+    monkeypatch.setattr("finance.exporting.build_formula_workbook", fail)
+    with pytest.raises(ValueError, match="controlled export failure"):
+        process_formula_export(job.pk)
+    monkeypatch.undo()
+
+    stats = process_formula_export(job.pk)
+    job.refresh_from_db()
+    assert stats["rows"] == 5
+    assert job.status == "succeeded"
+    assert Path(job.path).read_bytes()[:2] == b"PK"
+    assert not list(Path(job.path).parent.glob(f"{job.pk}.*.tmp"))
+
+
 def test_formula_workbook_rejects_unclassified_label_collision(workspace):
     from decimal import Decimal