c# - SSLStream 读取无效数据 + KB3147458 SSLStream 错误(？)

Question

当远程客户端未发送任何内容时，我遇到了 SSLStream 返回一些数据的问题。当服务器正在监听新命令时，我遇到了这个问题。如果服务器没有收到新的请求，ReadMessage() 函数应该捕获一个 IOException，因为 SSLStream 的读取超时。问题发生在第二次执行 sslStream.Read() 时，它似乎读取了客户端未发送的 5 个字节。所以问题按以下顺序发生:

-> ReadMessage() -> sslstream.Read() -> 如预期的那样捕获超时异常

-> ReadMessage() -> sslstream.Read() -> 未捕获超时异常，即使客户端未发送任何内容也读取了 5 个字节

-> ReadMessage() -> sslstream.Read() -> 如预期的那样捕获超时异常

-> ReadMessage() -> sslstream.Read() -> 未捕获超时异常，即使客户端未发送任何内容也读取了 5 个字节...

等等..

    public void ClientHandle(object obj)
    {
        nRetry = MAX_RETRIES;

        // Open connection with the client
        if (Open() == OPEN_SUCCESS)
        {
            String request = ReadMessage();
            String response = null;

            // while loop for the incoming commands from client
            while (!String.IsNullOrEmpty(request))
            {
                Console.WriteLine("[{0}] {1}", RemoteIPAddress, request);

                response = Execute(request);

                // If QUIT was received, close the connection with the client
                if (response.Equals(QUIT_RESPONSE))
                {
                    // Closing connection
                    Console.WriteLine("[{0}] {1}", RemoteIPAddress, response);

                    // Send QUIT_RESPONSE then return and close this thread
                    SendMessage(response);
                    break;
                }

                // If another command was received, send the response to the client
                if (!response.StartsWith("TIMEOUT"))
                {
                    // Reset nRetry
                    nRetry = MAX_RETRIES;

                    if (!SendMessage(response))
                    {
                        // Couldn't send message
                        Close();
                        break;
                    }
                }


                // Wait for new input request from client
                request = ReadMessage();

                // If nothing was received, SslStream timeout occurred
                if (String.IsNullOrEmpty(request))
                {
                    request = "TIMEOUT";
                    nRetry--;

                    if (nRetry == 0)
                    {
                        // Close everything
                        Console.WriteLine("Client is unreachable. Closing client connection.");
                        Close();
                        break;
                    }
                    else
                    {
                        continue;
                    }
                }
            }

            Console.WriteLine("Stopped");
        }
    }



    public String ReadMessage()
    {
        if (tcpClient != null)
        {
            int bytes = -1;
            byte[] buffer = new byte[MESSAGE_SIZE];

            try
            {
                bytes = sslStream.Read(buffer, 0, MESSAGE_SIZE);
            }
            catch (ObjectDisposedException)
            {
                // Streams were disposed
                return String.Empty;
            }
            catch (IOException)
            {
                return String.Empty;
            }
            catch (Exception)
            {
                // Some other exception occured
                return String.Empty;
            }

            if (bytes != MESSAGE_SIZE)
            {
                return String.Empty;
            }

            // Return string read from the stream
            return Encoding.Unicode.GetString(buffer, 0, MESSAGE_SIZE).Replace("\0", String.Empty);
        }

        return String.Empty;
    }


    public bool SendMessage(String message)
    {
        if (tcpClient != null)
        {
            byte[] data = CreateMessage(message);

            try
            {
                // Write command message to the stream and send it
                sslStream.Write(data, 0, MESSAGE_SIZE);
                sslStream.Flush();
            }
            catch (ObjectDisposedException)
            {
                // Streamers were disposed
                return false;
            }
            catch (IOException)
            {
                // Error while trying to access streams or connection timedout
                return false;
            }
            catch (Exception)
            {
                return false;
            }

            // Data sent successfully
            return true;
        }

        return false;
    }

   private byte[] CreateMessage(String message)
    {
        byte[] data = new byte[MESSAGE_SIZE];

        byte[] messageBytes = Encoding.Unicode.GetBytes(message);

        // Can't exceed MESSAGE_SIZE parameter (max message size in bytes)
        if (messageBytes.Length >= MESSAGE_SIZE)
        {
            throw new ArgumentOutOfRangeException("message", String.Format("Message string can't be longer than {0} bytes", MESSAGE_SIZE));
        }

        for (int i = 0; i < messageBytes.Length; i++)
        {
            data[i] = messageBytes[i];
        }
        for (int i = messageBytes.Length; i < MESSAGE_SIZE; i++)
        {
            data[i] = messageBytes[messageBytes.Length - 1];
        }

        return data;
    }

客户端也使用完全相同的 ReadMessage()、SendMessage() 和 CreateMessage() 函数向服务器发送消息。 MESSAGE_SIZE 常量也相同，设置为 2048。

Answer 1

问题是我在超时后重新使用了 SSLStream。所以我只是通过删除 nRetry 变量并设置更长的超时来解决问题。相关的 MSDN 文章说 SSLStream 将在超时异常 ( https://msdn.microsoft.com/en-us/library/system.net.security.sslstream(v=vs.110).aspx ) 后返回垃圾:

SslStream assumes that a timeout along with any other IOException when one is thrown from the inner stream will be treated as fatal by its caller. Reusing a SslStream instance after a timeout will return garbage. An application should Close the SslStream and throw an exception in these cases.

另一个问题是 Windows 更新 KB3147458(Windows 10 4 月的更新)更改了读取功能的行为。看起来 SSLStream 实现中的某些内容发生了变化，现在它每次返回 2 个部分的数据，1 个字节和其余字节。实际上 MSDN 文档并没有说 Read() 函数将一步返回所有请求的字节，并且提供的示例使用 do-while 循环来读取确切的字节数。所以我认为 Read() 函数不能保证一次读取所有请求的确切字节数，可能需要更多的读取迭代。

SSLstream 工作正常，因此没有损坏。您只需要注意并使用 do-while 循环并检查是否正确读取了所有字节。

我更改了这里显示的代码以解决我遇到的错误。

    public String ReadMessage()
    {
        if (tcpClient != null)
        {
            int bytes = -1, offset = 0;
            byte[] buffer = new byte[MESSAGE_SIZE];

            try
            {
                // perform multiple read iterations 
                // and check the number of bytes received
                while (offset < MESSAGE_SIZE)
                {
                    bytes = sslStream.Read(buffer, offset, MESSAGE_SIZE - offset);
                    offset += bytes;

                    if (bytes == 0)
                    {
                        return String.Empty;
                    }
                }
            }
            catch (Exception)
            {
                // Some exception occured
                return String.Empty;
            }

            if (offset != MESSAGE_SIZE)
            {
                return String.Empty;
            }

            // Return string read from the stream
            return Encoding.Unicode.GetString(buffer, 0, MESSAGE_SIZE).Replace("\0", String.Empty);
        }

        return String.Empty;
    }