[imp] IMAP sessions not starting correctly

[Michael Menge]

Hi Jens,

Quoting Jens Wahnes <wahnes at uni-koeln.de>:

> We're using Horde along with the IMAP Proxy originally developed for  
> the Squirrelmail project.  While this works out quite well most of  
> the time, there are, however, occasional problems with IMAP sessions  
> not working properly.  In the IMAP proxy's log file, there would be  
> a line reading "IMAP_Line_Read(): connection closed prematurely".   
> Since we were not able to forcefully produce this behavior, it has  
> always been hard to debug.
>
> Some time ago, we got "lucky" and this happened on one of our test  
> systems as well.  Before, it had only occured on the "production"  
> server, where Horde's debug level is lower and we cannot experiment  
> like we can on the test system.  I had always considered this to be  
> a problem of the IMAP proxy, but now it seems to me it might be  
> Horde's IMAP client causing this.  However, it's still very  
> difficult to see what actually is the cause of this - I couldn't  
> really find a way to debug this.  Maybe someone can give me a hint?
>
> When the problem occured, I did several tests on the system to rule  
> out different areas where the problem might be located.  For one,  
> restarting the IMAP proxy didn't help.  Also, the problem did  
> persist through the reload/restart of the Apache server running  
> Horde, so it can't be some strange bug with the opcode cache or  
> something like that.  Thirdly, the problem did not occur when using  
> (a) another browser from the same PC to connect to Horde using  
> another username to login and (b) using the same username as before  
> to login.  So it seems the problem is somehow tied to a specific  
> session within Horde.
>
> ...
>
> Any suggestions on how to further investigate this problem would be  
> very much appreciated.
>

We have seen a similar problem on our servers that might be related:
We have sporadic cases where user are able to login to horde, but
are than unable to access there mails in IMP because
"Mail server denied authentication". We use IMP for Horde Authentication,
and on the Log-files we see one successful login followed by many faild
logins.  We are pretty sure that the user didn't change password in between.
So we suspected that the password was not stored correct in the session,
got somehow corrupted or horde is unable to retrieve/decode the  
correct password.

We use horde_hashtable with Redis as session storage. But we had to  
disable session
tracking because of performance impact, so i was unable to take a  
closer look at the
problematic session.

Software
Mailserver: Cyrus IMAP v2.4.17 (Murder configuration)

Webmailer: php-5.4.16-36.el7_1.x86_64
            horde                5.2.8
            imp                 6.2.11
            Horde_HashTable      1.2.3
            Predis               1.0.3

Redis-Server redis-2.8.19-2.el7.x86_64


--------------------------------------------------------------------------------
M.Menge                                Tel.: (49) 7071/29-70316
Universität Tübingen                   Fax.: (49) 7071/29-5912
Zentrum für Datenverarbeitung          mail:  
michael.menge at zdv.uni-tuebingen.de
Wächterstraße 76
72074 Tübingen