fix: 校验守门按字节+递归长度+非dict拒绝

- 体积守门改 UTF-8 字节数（原按字符数，"汉"*1500 约 4.5KB 可绕过 4096 上限）
- 字符串长度检查并入 _walk_props 递归，嵌套字符串同样受 MAX_STR_LEN 约束
  （顺序：体积先行，故同一值既超长又超体积时报 properties_too_large）
- properties 传了但非 dict（[]/""/0/None）不再被 or {} 静默放行，缺省键仍放行

Co-Authored-By: Claude Code <noreply@anthropic.com>

server/tracker/services/validation.py

@@ -16,27 +16,32 @@ def sanitize_url(url: str) -> str:
     return p._replace(query=urlencode(kept)).geturl()
 
 def _walk_props(v, depth=0):
-    """单次递归同时做深度检查与敏感键扫描（dict 所有层级的键都过 _SENSITIVE）。
-    返回 (depth_ok, sensitive_hit)。深度超限即停止下探，防恶意深嵌套递归爆栈。"""
+    """单次递归同时做深度检查、敏感键扫描与字符串超长检查。
+    dict 所有层级的键都过 _SENSITIVE，所有层级的字符串都受 MAX_STR_LEN 约束。
+    返回 (depth_ok, sensitive_hit, str_too_long)。深度超限即停止下探，防恶意深嵌套递归爆栈。"""
     if depth > C.MAX_PROP_DEPTH:
-        return False, False
+        return False, False, False
     if isinstance(v, dict):
-        depth_ok, sens = True, False
+        depth_ok, sens, too_long = True, False, False
         for k, x in v.items():
             if _SENSITIVE.search(str(k)):
                 sens = True
-            d, s = _walk_props(x, depth + 1)
+            d, s, l = _walk_props(x, depth + 1)
             depth_ok = depth_ok and d
             sens = sens or s
-        return depth_ok, sens
+            too_long = too_long or l
+        return depth_ok, sens, too_long
     if isinstance(v, list):
-        depth_ok, sens = True, False
+        depth_ok, sens, too_long = True, False, False
         for x in v:
-            d, s = _walk_props(x, depth + 1)
+            d, s, l = _walk_props(x, depth + 1)
             depth_ok = depth_ok and d
             sens = sens or s
-        return depth_ok, sens
-    return True, False
+            too_long = too_long or l
+        return depth_ok, sens, too_long
+    if isinstance(v, str) and len(v) > C.MAX_STR_LEN:
+        return True, False, True
+    return True, False, False
 
 def validate_event(ev) -> str | None:
     """返回 None 表示通过；否则返回拒绝原因码。类型/白名单/体积/深度全在此守门。"""
@@ -58,23 +63,23 @@ def validate_event(ev) -> str | None:
     skew = (timezone.now() - occ).total_seconds()
     if abs(skew) > C.CLOCK_SKEW_REJECT_SEC:
         return "occurred_at_out_of_window"
-    props = ev.get("properties") or {}
+    props = ev.get("properties", {})
     if not isinstance(props, dict) or len(props) > C.MAX_PROP_KEYS:
-        return "properties_invalid"
+        return "properties_invalid"          # 传了但非 dict（[]/""/0/None）一律拒
     # 敏感键扫描（含嵌套层级）先于属性白名单：白名单内无任何键命中敏感模式，
     # 若放在白名单之后，sensitive_field 将不可达（见 test_sensitive_property_rejected）。
-    depth_ok, sensitive_hit = _walk_props(props)
+    depth_ok, sensitive_hit, str_too_long = _walk_props(props)
     if sensitive_hit:
         return "sensitive_field"
     if not set(props) <= C.EVENT_PROP_WHITELIST.get(ev["event_name"], set()):
         return "property_not_allowed"
     if not depth_ok:
         return "properties_depth"
-    if len(json.dumps(props, ensure_ascii=False, default=str)) > C.MAX_PROP_JSON_BYTES:
+    # 体积按 UTF-8 字节数守门（汉字多字节，按字符数会被绕过）
+    if len(json.dumps(props, ensure_ascii=False, default=str).encode("utf-8")) > C.MAX_PROP_JSON_BYTES:
         return "properties_too_large"
-    for v in props.values():
-        if isinstance(v, str) and len(v) > C.MAX_STR_LEN:
-            return "properties_too_long"
+    if str_too_long:
+        return "properties_too_long"
     if len(ev.get("path") or "") > C.MAX_PATH_LEN:
         ev["path"] = ev["path"][:C.MAX_PATH_LEN]
     if len(ev.get("title") or "") > C.MAX_TITLE_LEN:

server/tracker/tests/test_validation.py

@@ -47,3 +47,13 @@ def test_nested_sensitive_key_rejected():
 
 def test_naive_datetime_rejected():
     assert validate_event(_ev(occurred_at=NOW.replace(tzinfo=None))) == "invalid_occurred_at"
+
+def test_prop_size_gate_counts_bytes():
+    r = validate_event(_ev(properties={"utm": {"a": "汉" * 1500}}))
+    assert r == "properties_too_large"      # 字符数约 2K 未超，UTF-8 约 4.5KB 超 4096，须按字节算
+
+def test_nested_string_length_capped():
+    assert validate_event(_ev(properties={"utm": {"a": "x" * 600}})) == "properties_too_long"
+
+def test_falsy_non_dict_properties_rejected():
+    assert validate_event(_ev(properties=[])) == "properties_invalid"