This patch was previously posted here: http://lists.gnu.org/archive/html/qemu-devel/2009-02/msg00820.html In the case where the TLS handshake does *not* block on I/O, QEMU sends the next 'start sub-auth' message twice. This seriously confuses the VNC client :-) Fortunately the chances of the handshake not blocking are close to zero for a TCP socket, which is why it has not been noticed thus far. Even with both client & server on localhost, I can only hit the bug 1 time in 20. NB, the diff context here is not too informative. If you look at the full code you'll see that a few lines early we called vnc_start_tls() which called vnc_continue_handshake() which called the method start_auth_vencrypt_subauth(). Hence, fixing the bug, just involves removing the 2nd bogus call to start_auth_vencrypt_subauth() as per this patch. vnc.c | 8 -------- 1 file changed, 8 deletions(-) Signed-off-by: Daniel P. Berrange diff -r ff004fb525e7 vnc.c --- a/vnc.c Thu Feb 19 11:26:55 2009 +0000 +++ b/vnc.c Thu Feb 19 11:27:44 2009 +0000 @@ -2096,14 +2096,6 @@ static int protocol_client_vencrypt_auth VNC_DEBUG("Failed to complete TLS\n"); return 0; } - - if (vs->wiremode == VNC_WIREMODE_TLS) { - VNC_DEBUG("Starting VeNCrypt subauth\n"); - return start_auth_vencrypt_subauth(vs); - } else { - VNC_DEBUG("TLS handshake blocked\n"); - return 0; - } } return 0; }