src/pobsync_backend/retention.py

@@ -103,6 +103,7 @@ def run_sql_retention_apply(
                 raise ConfigError(f"Refusing to delete unsupported snapshot kind: {snap_kind!r}")
 
             path = _snapshot_delete_path(path=Path(snap_path), dirname=dirname)
+            _validate_snapshot_delete_path(host=host, kind=snap_kind, path=path, dirname=dirname)
             reason = str(item.get("reason") or "outside retention policy")
             if not path.exists():
                 actions.append(f"skip missing {snap_kind}/{dirname}")
@@ -339,14 +340,55 @@ def _validate_incomplete_delete_path(*, host: str, path: Path, dirname: str) ->
         raise ConfigError(f"Refusing to delete incomplete snapshot outside host backup root: {path}")
 
 
+def _validate_snapshot_delete_path(*, host: str, kind: str, path: Path, dirname: str) -> None:
+    if kind not in {SnapshotRecord.Kind.SCHEDULED, SnapshotRecord.Kind.MANUAL}:
+        raise ConfigError(f"Refusing to delete unsupported snapshot kind: {kind!r}")
+    path_parts = path.parts
+    if path.name != dirname or kind not in path_parts or host not in path_parts:
+        raise ConfigError(f"Refusing to delete unexpected snapshot path: {path}")
+    kind_index = path_parts.index(kind)
+    if kind_index == 0 or path_parts[kind_index - 1] != host:
+        raise ConfigError(f"Refusing to delete snapshot outside host backup root: {path}")
+
+
 def _remove_snapshot_tree(path: Path) -> None:
-    _make_directories_user_writable(path)
+    _make_snapshot_tree_user_removable(path)
-    shutil.rmtree(path)
+    shutil.rmtree(path, onexc=_retry_remove_with_user_permissions)
 
 
-def _make_directories_user_writable(path: Path) -> None:
+def _make_snapshot_tree_user_removable(path: Path) -> None:
-    for directory in [path, *[child for child in path.rglob("*") if child.is_dir() and not child.is_symlink()]]:
+    stack = [path]
-        mode = directory.stat().st_mode
+    while stack:
-        if mode & stat.S_IWUSR:
+        directory = stack.pop()
+        if directory.is_symlink():
             continue
-        directory.chmod(mode | stat.S_IWUSR)
+        _make_path_user_removable(directory)
+        try:
+            children = list(directory.iterdir())
+        except OSError:
+            continue
+        for child in children:
+            if child.is_dir() and not child.is_symlink():
+                stack.append(child)
+
+
+def _retry_remove_with_user_permissions(function: Any, path: str, excinfo: BaseException) -> None:
+    failed_path = Path(path)
+    _make_path_user_removable(failed_path)
+    function(path)
+
+
+def _make_path_user_removable(path: Path) -> None:
+    try:
+        mode = path.stat().st_mode
+    except OSError:
+        return
+    wanted = stat.S_IRUSR | stat.S_IWUSR
+    if path.is_dir() and not path.is_symlink():
+        wanted |= stat.S_IXUSR
+    if mode & wanted == wanted:
+        return
+    try:
+        path.chmod(mode | wanted)
+    except OSError:
+        return

src/pobsync_backend/tests/test_sql_retention.py

@@ -154,6 +154,68 @@ class SqlRetentionTests(TestCase):
                 ],
             )
 
+    def test_apply_deletes_snapshot_with_non_traversable_nested_directory(self) -> None:
+        with TemporaryDirectory() as tmp:
+            prefix = Path(tmp) / "home"
+            host = HostConfig.objects.create(
+                host="web-01",
+                address="web-01.example.test",
+                retention_daily=0,
+                retention_weekly=0,
+                retention_monthly=0,
+                retention_yearly=0,
+            )
+            old_dir = Path(tmp) / "backups" / host.host / "scheduled" / "20260518-021500Z__OLD"
+            restricted_dir = old_dir / "data" / "var" / "lib" / "snapd" / "void"
+            restricted_dir.mkdir(parents=True)
+            restricted_dir.joinpath("state").write_text("preserved permissions\n")
+            restricted_dir.chmod(0)
+            new_dir = Path(tmp) / "backups" / host.host / "scheduled" / "20260519-021500Z__NEW"
+            new_dir.mkdir(parents=True)
+            old = self._snapshot(host, old_dir.name, path=str(old_dir))
+            self._snapshot(host, new_dir.name, path=str(new_dir))
+
+            result = run_sql_retention_apply(
+                prefix=prefix,
+                host=host.host,
+                kind="scheduled",
+                protect_bases=False,
+                yes=True,
+                max_delete=1,
+                acquire_lock=False,
+            )
+
+            self.assertFalse(old_dir.exists())
+            self.assertFalse(SnapshotRecord.objects.filter(pk=old.pk).exists())
+            self.assertEqual(result["deleted"][0]["dirname"], old.dirname)
+
+    def test_apply_rejects_scheduled_snapshot_path_outside_host_kind_directory(self) -> None:
+        host = HostConfig.objects.create(
+            host="web-01",
+            address="web-01.example.test",
+            retention_daily=0,
+            retention_weekly=0,
+            retention_monthly=0,
+            retention_yearly=0,
+        )
+        self._snapshot(
+            host,
+            "20260518-021500Z__OLD",
+            path="/backups/web-01/manual/20260518-021500Z__OLD",
+        )
+        self._snapshot(host, "20260519-021500Z__NEW")
+
+        with self.assertRaisesRegex(ConfigError, "unexpected snapshot path"):
+            run_sql_retention_apply(
+                prefix=Path("/tmp/pobsync-test"),
+                host=host.host,
+                kind="scheduled",
+                protect_bases=False,
+                yes=True,
+                max_delete=1,
+                acquire_lock=False,
+            )
+
     def test_apply_respects_max_delete(self) -> None:
         host = HostConfig.objects.create(
             host="web-01",
@@ -213,6 +275,36 @@ class SqlRetentionTests(TestCase):
             self.assertEqual(purged.action, PurgedSnapshot.Action.INCOMPLETE_CLEANUP)
             self.assertEqual(purged.reason, "manual incomplete cleanup")
 
+    def test_incomplete_cleanup_deletes_non_traversable_nested_directory(self) -> None:
+        with TemporaryDirectory() as tmp:
+            prefix = Path(tmp) / "home"
+            host = HostConfig.objects.create(host="web-01", address="web-01.example.test")
+            incomplete_dir = Path(tmp) / "backups" / host.host / ".incomplete" / "20260519-031500Z__BROKEN01"
+            restricted_dir = incomplete_dir / "data" / "var" / "lib" / "snapd" / "void"
+            restricted_dir.mkdir(parents=True)
+            restricted_dir.joinpath("state").write_text("interrupted\n")
+            restricted_dir.chmod(0)
+            record = SnapshotRecord.objects.create(
+                host=host,
+                kind=SnapshotRecord.Kind.INCOMPLETE,
+                dirname=incomplete_dir.name,
+                path=str(incomplete_dir),
+                status="failed",
+                started_at=datetime(2026, 5, 19, 3, 15, tzinfo=timezone.utc),
+            )
+
+            result = run_incomplete_cleanup(
+                prefix=prefix,
+                host=host.host,
+                yes=True,
+                max_delete=1,
+                acquire_lock=False,
+            )
+
+            self.assertFalse(incomplete_dir.exists())
+            self.assertFalse(SnapshotRecord.objects.filter(pk=record.pk).exists())
+            self.assertEqual(result["deleted"][0]["dirname"], incomplete_dir.name)
+
     def test_incomplete_cleanup_respects_max_delete(self) -> None:
         host = HostConfig.objects.create(host="web-01", address="web-01.example.test")
         SnapshotRecord.objects.create(