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POSSL renegotiation with full duplex socket communication
 

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    <p>I have a very simple client-server with one blocking socket doing full-duplex communication. I've enabled SSL/TLS to the application. The model is that of a typical producer-consumer. The client produces the data, sends it to the server and the server processes them. The only catch is that, once in a while the server sends data back to the client which the client handles accordingly. Below is a very simple pseudo code of the application:</p> <blockquote> <pre><code> 1 Client: 2 ------- 3 while (true) 4 { 5 if (poll(pollin, timeout=0) || 0 &lt; SSL_pending(ssl)) 6 { 7 SSL_read(); 8 // Handle WANT_READ or WANT_WRITE appropriately. 9 // If no error, handle the received control message. 10 } 11 // produce data. 12 while (!poll(pollout)) 13 ; // Wait until the pipe is ready for a send(). 14 SSL_write(); 15 // Handle WANT_READ or WANT_WRITE appropriately. 16 if (time to renegotiate) 17 SSL_renegotiate(ssl); 18 } 19 20 Server: 21 ------- 22 while (true) 23 { 24 if (poll(pollin, timeout=1s) || 0 &lt; SSL_pending(ssl)) 25 { 26 SSL_read(); 27 // Handle WANT_READ or WANT_WRITE appropriately. 28 // If no error, consume data. 29 } 30 if (control message needs to be sent) 31 { 32 while (!poll(pollout)) 33 ; // Wait until the pipe is ready for a send(). 34 SSL_write(); 35 // Handle WANT_READ or WANT_WRITE appropriately. 36 } 37 } </code></pre> </blockquote> <p>The trouble happens when, for testing purposes, I force SSL renegotiation (lines 16-17). The session starts nice and easy, but after a while, I get the following errors:</p> <pre><code>Client: ------- error:140940F5:SSL routines:SSL3_READ_BYTES:unexpected record Server: ------- error:140943F2:SSL routines:SSL3_READ_BYTES:sslv3 alert unexpected message </code></pre> <p>Turns out, around the same time that the client initiates a renegotiation (line 14), the server ends up sending application data to the client (line 34). The client as part of the renegotiation process receives this application data and bombs with a "unexpected record" error. Similarly, when the server does the subsequent receive (line 26), it ends up receiving a renegotiation data when it was expecting application data.</p> <p>What am I doing wrong? How should I handle/test SSL renegotiations with a full-duplex channel. Note that, there are no threads involved. It's a simple single threaded model with reads/writes happening on either end of the socket.</p> <p><strong>UPDATE</strong> : To verify that there is nothing wrong with the application that I have written, I could even reproduce this quite comfortably with OpenSSL's s_client and s_server implementations. I started a s_server and once the s_client got connected to the server, I programmatically send a bunch of application data from the server to the client and a bunch of 'R' (renegotiation requests) from the client to the server. Eventually, they both fail in exactly the same manner as described above.</p> <pre><code>s_client: RENEGOTIATING 4840:error:140940F5:SSL routines:SSL3_READ_BYTES:unexpected record:s3_pkt.c:1258: s_server: Read BLOCK ERROR 4838:error:140943F2:SSL routines:SSL3_READ_BYTES:sslv3 alert unexpected message:s3_pkt.c:1108:SSL alert number 10 4838:error:140940E5:SSL routines:SSL3_READ_BYTES:ssl handshake failure:s3_pkt.c:1185: </code></pre> <p><strong>UPDATE 2:</strong> Ok. As suggested by David, I reworked the test application to use non-blocking sockets and always do SSL_read and SSL_write first and do the select based on what they return and I still get the same errors during renegotiations (SSL_write ends up getting application data from the other side in the midst of renegotiation). The question is, at any point in time, if SSL_read returns WANT_READ, can I assume it is because there is nothing in the pipe and go ahead with SSL_write since I have something to write? If not, that's probably why I end up with errors. Either that, or I am doing the renegotiation all wrong. Note, if SSL_read returns WANT_WRITE, I always do a select and call SSL_read again.</p>
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