[gnutls-devel] gnutls 3.2.6+: connection to api.dreamhost.com hangs

[Andreas Metzler]

Hello,

this is http://bugs.debian.org/733039 reported by Neil Roeth.

Recent versions of gnutls fail at connecting to api.dreamhost.com,
they just hang. Git bisect shows that breakage started with this commit:

-------
3ff8313d3eb53eed1a509e45d5f5103c87c1900d is the first bad commit
commit 3ff8313d3eb53eed1a509e45d5f5103c87c1900d
Author: Nikos Mavrogiannopoulos <nmav at gnutls.org>
Date:   Wed Oct 23 18:53:45 2013 +0200

    Added camellia-gcm into the default priority levels, and prioritized
    GCM over CBC everywhere.
-------

Daniel Kahn Gillmor added these interesting pieces of information:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=733039#22
|------------------------------------------------------
| I can confirm that 3.2.7 seems to hang for me, when i do:
| 
|  gnutls-cli --priority NORMAL api.dreamhost.com
| 
| However, i can connect cleanly with:
| 
|  gnutls-cli --priority NORMAL:-DHE-DSS api.dreamhost.com
| 
| I can avoid the same hang if i substitute any large-ish class of ciphers
| anywhere i put DHE-DSS above.
| 
| Looking at the traffic on the wire, it looks like the non-hanging
| connections offer a ClientHello of size < 256 bytes, while the hanging
| connections have size >= 256 bytes.
| 
| this smells a lot like the F5 bug with certain sizes of TLS handshakes,
| being misinterpreted as SSLv2, as reported by Xiaoyong Wu:
| 
|  http://thread.gmane.org/gmane.ietf.tls/11187/focus=11227
| 
| The way to resolve this would be:  if the client hello is >= 256 byees,
| but < 512 bytes, add a meaningless extension to push the size of the
| client hello above 512 bytes.
| 
| I haven't tested this yet, unfortunately.
| 
|         --dkg
|------------------------------------------------------

cu Andreas

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