Reject invalid Tailscale discovery JSON (#1556)

* Reject invalid Tailscale discovery JSON

* Guard nested Tailscale IP shapes

src/model_discovery.py

@@ -16,6 +16,23 @@ _hosts_cache_time: float = 0
 _HOSTS_CACHE_TTL = 60  # seconds
 
 
+def _parse_tailscale_status(raw: str) -> Dict[str, Any]:
+    try:
+        data = json.loads(raw)
+    except (TypeError, json.JSONDecodeError):
+        return {}
+    return data if isinstance(data, dict) else {}
+
+
+def _first_tailscale_ipv4(value: Any) -> Optional[str]:
+    if not isinstance(value, list):
+        return None
+    for ip in value:
+        if isinstance(ip, str) and "." in ip:
+            return ip
+    return None
+
+
 def discover_tailscale_hosts() -> List[str]:
     """Discover online Tailscale peers, returning their IPv4 addresses."""
     global _hosts_cache, _hosts_cache_time
@@ -33,17 +50,21 @@ def discover_tailscale_hosts() -> List[str]:
         if result.returncode != 0:
             return hosts
 
-        data = json.loads(result.stdout)
+        data = _parse_tailscale_status(result.stdout)
+        if not data:
+            return hosts
 
         # Add self
-        self_ips = data.get("Self", {}).get("TailscaleIPs", [])
-        for ip in self_ips:
-            if "." in ip:  # IPv4 only
-                hosts.append(ip)
-                break
+        self_data = data.get("Self") if isinstance(data.get("Self"), dict) else {}
+        self_ip = _first_tailscale_ipv4(self_data.get("TailscaleIPs"))
+        if self_ip:
+            hosts.append(self_ip)
 
         # Add online peers (skip funnel-ingress-nodes and android devices)
-        for peer in data.get("Peer", {}).values():
+        peers = data.get("Peer") if isinstance(data.get("Peer"), dict) else {}
+        for peer in peers.values():
+            if not isinstance(peer, dict):
+                continue
             if not peer.get("Online"):
                 continue
             hostname = peer.get("HostName", "")
@@ -52,11 +73,9 @@ def discover_tailscale_hosts() -> List[str]:
             os_name = peer.get("OS", "")
             if os_name == "android":
                 continue
-            peer_ips = peer.get("TailscaleIPs", [])
-            for ip in peer_ips:
-                if "." in ip:  # IPv4 only
-                    hosts.append(ip)
-                    break
+            peer_ip = _first_tailscale_ipv4(peer.get("TailscaleIPs"))
+            if peer_ip:
+                hosts.append(peer_ip)
 
         _hosts_cache = hosts
         _hosts_cache_time = now

tests/test_model_discovery_status.py

@@ -0,0 +1,37 @@
+from src import model_discovery
+
+
+def test_parse_tailscale_status_rejects_wrong_shapes():
+    assert model_discovery._parse_tailscale_status("{bad") == {}
+    assert model_discovery._parse_tailscale_status("[]") == {}
+    assert model_discovery._parse_tailscale_status('{"Self": {}}') == {"Self": {}}
+
+
+def test_discovery_ignores_invalid_peer_rows(monkeypatch):
+    class Result:
+        returncode = 0
+        stdout = '{"Self":{"TailscaleIPs":["100.1.1.1"]},"Peer":{"bad":"row","ok":{"Online":true,"HostName":"box","OS":"linux","TailscaleIPs":["100.1.1.2"]}}}'
+
+    monkeypatch.setattr(model_discovery.subprocess, "run", lambda *a, **k: Result())
+    model_discovery._hosts_cache = []
+    model_discovery._hosts_cache_time = 0
+
+    assert model_discovery.discover_tailscale_hosts() == ["100.1.1.1", "100.1.1.2"]
+
+
+def test_discovery_ignores_invalid_tailscale_ip_shapes(monkeypatch):
+    class Result:
+        returncode = 0
+        stdout = (
+            '{"Self":{"TailscaleIPs":"100.1.1.1"},'
+            '"Peer":{'
+            '"string_ips":{"Online":true,"HostName":"bad","OS":"linux","TailscaleIPs":"100.1.1.2"},'
+            '"mixed_ips":{"Online":true,"HostName":"ok","OS":"linux","TailscaleIPs":[null,123,"100.1.1.3"]}'
+            '}}'
+        )
+
+    monkeypatch.setattr(model_discovery.subprocess, "run", lambda *a, **k: Result())
+    model_discovery._hosts_cache = []
+    model_discovery._hosts_cache_time = 0
+
+    assert model_discovery.discover_tailscale_hosts() == ["100.1.1.3"]