Disable socket inheritance on Windows and macOS

We already disabled it on Linux.  Doing the same for Windows and macOS.

Author: stephentoub

src/Common/src/Interop/Windows/Winsock/Interop.WSASocketW.SafeCloseSocket.cs

@@ -19,6 +19,7 @@ internal enum SocketConstructorFlags
             WSA_FLAG_MULTIPOINT_C_LEAF = 0x04,
             WSA_FLAG_MULTIPOINT_D_ROOT = 0x08,
             WSA_FLAG_MULTIPOINT_D_LEAF = 0x10,
+            WSA_FLAG_NO_HANDLE_INHERIT = 0x80,
         }
 
         [DllImport(Interop.Libraries.Ws2_32, CharSet = CharSet.Unicode, SetLastError = true)]

src/Common/src/System/Net/SafeCloseSocket.Windows.cs

@@ -217,7 +217,7 @@ private SocketError InnerReleaseHandle()
 
             internal static InnerSafeCloseSocket CreateWSASocket(AddressFamily addressFamily, SocketType socketType, ProtocolType protocolType)
             {
-                InnerSafeCloseSocket result = Interop.Winsock.WSASocketW(addressFamily, socketType, protocolType, IntPtr.Zero, 0, Interop.Winsock.SocketConstructorFlags.WSA_FLAG_OVERLAPPED);
+                InnerSafeCloseSocket result = Interop.Winsock.WSASocketW(addressFamily, socketType, protocolType, IntPtr.Zero, 0, Interop.Winsock.SocketConstructorFlags.WSA_FLAG_OVERLAPPED | Interop.Winsock.SocketConstructorFlags.WSA_FLAG_NO_HANDLE_INHERIT);
                 if (result.IsInvalid)
                 {
                     result.SetHandleAsInvalid();

src/Common/src/System/Net/SocketProtocolSupportPal.Windows.cs

@@ -63,7 +63,7 @@ private static bool IsProtocolSupported(AddressFamily af)
 
             try
             {
-                s = Interop.Winsock.WSASocketW(af, SocketType.Dgram, 0, IntPtr.Zero, 0, 0);
+                s = Interop.Winsock.WSASocketW(af, SocketType.Dgram, 0, IntPtr.Zero, 0, (int)Interop.Winsock.SocketConstructorFlags.WSA_FLAG_NO_HANDLE_INHERIT);
 
                 if (s == IntPtr.Zero)
                 {

src/Native/Unix/System.Native/pal_networking.c

@@ -1978,7 +1978,15 @@ int32_t SystemNative_Socket(int32_t addressFamily, int32_t socketType, int32_t p
     platformSocketType |= SOCK_CLOEXEC;
 #endif
     *createdSocket = socket(platformAddressFamily, platformSocketType, platformProtocolType);
-    return *createdSocket != -1 ? Error_SUCCESS : SystemNative_ConvertErrorPlatformToPal(errno);
+    if (*createdSocket == -1)
+    {
+        return SystemNative_ConvertErrorPlatformToPal(errno);
+    }
+
+#ifndef SOCK_CLOEXEC
+    fcntl(ToFileDescriptor(*createdSocket), F_SETFD, FD_CLOEXEC); // ignore any failures; this is best effort
+#endif
+    return Error_SUCCESS;
 }
 
 int32_t SystemNative_GetAtOutOfBandMark(intptr_t socket, int32_t* atMark)