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Subject: RE: [gptalk] Group Policy Preferences: Environment Variable Expansion and Circular References

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DarraghOShaughnessy User is Offline

Posts:161

09/08/2010 11:38 AM
Thanks Darren. From: xxxxxxxxxxxxxxxx [mailto:xxxxxxxxxxxxxxxx] On Behalf Of Darren Mar-Elia Sent: 08 September 2010 03:14 To: xxxxxxxxxxxxxxxx Subject: RE: [gptalk] Group Policy Preferences: Environment Variable Expansion and Circular References Nothing back so far Darragh. Let me see if I can dig a little bit on my own around this. Darren From: xxxxxxxxxxxxxxxx [mailto:xxxxxxxxxxxxxxxx] On Behalf Of Darragh O'Shaughnessy Sent: Monday, September 06, 2010 3:53 AM To: xxxxxxxxxxxxxxxx Subject: RE: [gptalk] Group Policy Preferences: Environment Variable Expansion and Circular References Hi Darren, I wonder did the product team have anything to say on this. Still observing this behaviour in the wild. Regards, Darragh O'Shaughnessy From: xxxxxxxxxxxxxxxx [mailto:xxxxxxxxxxxxxxxx] On Behalf Of Darren Mar-Elia Sent: 20 August 2010 16:25 To: xxxxxxxxxxxxxxxx Subject: RE: [gptalk] Group Policy Preferences: Environment Variable Expansion and Circular References Darragh- I'll forward this to the product team. I agree with you that if this is really how its working, this would indicate a bug in the code. Darren From: xxxxxxxxxxxxxxxx [mailto:xxxxxxxxxxxxxxxx] On Behalf Of Darragh O'Shaughnessy Sent: Friday, August 20, 2010 8:10 AM To: xxxxxxxxxxxxxxxx Subject: [gptalk] Group Policy Preferences: Environment Variable Expansion and Circular References Hey guys, I have an interesting case for you to ponder. I have had an issue lately where users logging onto a machines will hand at 'Applying Settings' infinitely and never get to the desktop. After a days worth of detailed debugging using procmon/procexp/dbgview I was led to gpprefcl.dll. This little library appears to be responsible for environment variables in group policy preferences. What I found is that some users have circular references in their environment variables eg: CLASSPATH=c:\libs;%CLASSPATH% This would be a normal CLASSPATH setting if set from the command line and any of you java nerds out there will be familiar with it :-) Now, it appears that when gpprefcl.dll (to be exact the function therein whose name I haven't figured out yet!) expands this environment variable we get an infinite loop and processing of this client side extension never completes. This can be observed using pslist.exe or the like. You will see a thread running under winlogon that never exits and has a handles open to this .dll and is calling several functions therein. I've recreated it in my test vm lab. I'd be interested if anyone could add some insight here. I don't have the source code for the .dll so I cant see how it expands the variables or if it calls another native library to do that. If you look at the variables using the GUI i.e. System->Advanced->Environment Variables It would display as "CLASSPATH=c:\libs;c:\libs;%CLASSPATH%" which indicates to me that the circular reference is cut off after one expansion on the right hand side i.e. "%CLASSPATH%" is substituted with "c:\libs;%CLASSPATH%" once here whereas the .dll seems to recursively expand this. I'd love to bring this up with Microsoft's GPP Team but I have no idea how to do it. Regards, Darragh O'Shaughnessy

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Forums >GPTalk >GPTalk Mailing List > RE: [gptalk] Group Policy Preferences: Environment Variable Expansion and Circular References

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