agent: allow only public addresses as single-agent targets unless allowed_target_cidrs says otherwise

backend/shared/MoShiro.Measurement/Execution/BudgetGuard.cs

@@ -107,8 +107,8 @@ public sealed class BudgetGuard
     }
 
     /// <summary>
-    /// 目标在静态上可不可以接受：IP 字面量按 <c>allowed_target_cidrs</c> 检查；域名（包括 URL 里的）要解析之后才知道，
-    /// 这里只要求配置过白名单，运行时每次解析出的地址再用 <see cref="AddressAllowed"/> 检查。
+    /// 目标在静态上可不可以接受：IP 字面量直接用 <see cref="AddressAllowed"/> 判断；域名（包括 URL 里的）要解析之后才知道，
+    /// 这里先接受，运行时每次解析出的地址再逐个检查。
     /// </summary>
     public bool TargetAllowed(string? target)
     {
@@ -117,9 +117,13 @@ public sealed class BudgetGuard
             return false;
         }
 
-        return IPAddress.TryParse(host, out IPAddress? address) ? AddressAllowed(address) : _cidrs.Count > 0;
+        return !IPAddress.TryParse(host, out IPAddress? address) || AddressAllowed(address);
     }
 
+    /// <summary>
+    /// 这个地址能不能作为单个 Agent 任务的目标。<c>allowed_target_cidrs</c> 没配置时只允许公网地址（内网、回环、链路本地、组播等一律拒绝），
+    /// 防止被攻破的 Backend 借 Agent 探测它所在的内网；配置了就只允许列出的网段（包括内网段，由节点所有者显式决定）。
+    /// </summary>
     public bool AddressAllowed(IPAddress address)
     {
         if (address.IsIPv4MappedToIPv6)
@@ -127,6 +131,11 @@ public sealed class BudgetGuard
             address = address.MapToIPv4();
         }
 
+        if (_limits.AllowedTargetCidrs.Count == 0)
+        {
+            return IsPublic(address);
+        }
+
         foreach ((IPAddress network, int prefix) in _cidrs)
         {
             if (InCidr(address, network, prefix))
@@ -138,6 +147,28 @@ public sealed class BudgetGuard
         return false;
     }
 
+    private static readonly (IPAddress Network, int Prefix)[] s_nonPublic =
+    [
+        (IPAddress.Parse("0.0.0.0"), 8), (IPAddress.Parse("10.0.0.0"), 8), (IPAddress.Parse("100.64.0.0"), 10), (IPAddress.Parse("127.0.0.0"), 8),
+        (IPAddress.Parse("169.254.0.0"), 16), (IPAddress.Parse("172.16.0.0"), 12), (IPAddress.Parse("192.0.0.0"), 24), (IPAddress.Parse("192.168.0.0"), 16),
+        (IPAddress.Parse("198.18.0.0"), 15), (IPAddress.Parse("224.0.0.0"), 3),
+        (IPAddress.Parse("::"), 128), (IPAddress.Parse("::1"), 128), (IPAddress.Parse("fc00::"), 7), (IPAddress.Parse("fe80::"), 10), (IPAddress.Parse("ff00::"), 8),
+    ];
+
+    /// <summary>不是公网：私有、回环、链路本地、运营商级 NAT、组播、保留地址。</summary>
+    private static bool IsPublic(IPAddress address)
+    {
+        foreach ((IPAddress network, int prefix) in s_nonPublic)
+        {
+            if (InCidr(address, network, prefix))
+            {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
     private bool PortAllowed(KindSpec kind, ParamValues values)
     {
         if (!kind.Params.Any(p => p.Name == "port"))