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Message-ID: <536A3E80.2060602@breisch.org>
Date: Wed, 07 May 2014 10:09:04 -0400
From: "Chris J. Breisch" <chris DOT ml AT breisch DOT org>
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To: cygwin AT cygwin DOT com
Subject: Re: Microsoft Accounts (was Re: Problem with "None" Group on Non-Domain Members)
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Corinna Vinschen wrote:
> On May  7 13:57, Corinna Vinschen wrote:
>> I toyed around with the Microsoft Account a bit more.  And here's why
>> the primary group SID being identical to the user SID is not a good
>> idea:
>>
>>    Security checks.
>>
>> For instance:
>>
>>    $ echo $USER
>>    VMBERT8164+local_000
>>    $ screen
>>    Directory /tmp/uscreens/S-VMBERT8164+local_000 must have mode 700.
>>
>> Huh?
>>
>>    $ ls -l /tmp/uscreens/
>>    total 0
>>    drwxrwx---+ 1 VMBERT8164+local_000 VMBERT8164+local_000 0 May  7 12:44 S-VMBERT8164+local_000
>>
>> Uh Oh.
>>
>> This will be a problem with other security sensitive applications, too.
>> Sshd comes to mind.
>>
>> So I guess we really should make sure the primary group SID is some
>> valid group, not the user's SID.
>>
>> "None" is not an option since it's not in the user token group list.
>>
>> "Users" seems to be the best choice at first sight.
>>
>> Alternatively we could use the S-1-11-xxx SID of the Microsoft Account.
>> That would be in line with the idea to have a user-specific primary
>> group.
>>
>> Thoughts?
>
> And here's a problem which I'm not sure how to solve at all:
>
> When calling the latest mkpasswd, the primary group of the local
> user account backing the Microsoft Account will *still* be "None".
>
> The reason is that the local account is just the same old account
> as usual.  Its default primary group *is* "None".
>
> Only when logging in via the Micosoft Account email address, the
> user token will not reflect what's stored in the local SAM, but
> will have been changed by the OS as outlined in this thread.
>
> So, when a user decides to create a passwd file rather than using
> the SAM/DB code in Cygwin, the information generated by mkpasswd
> will not match the user token, and the primary group stored in
> /etc/passwd will not even be available at all in the user token.
>
> I have not the faintest idea how to workaround this schizophrenia.
>
>
> Corinna
>
Oh wow. It took me two reads of this to understand it. Caffeine is 
finally kicking in, I guess. Unless you just want to hard code the 
primary group that mkpasswd generates to "Users" for any account that it 
would tend to want to set as "None". That would be some smelly code though.

-- 
Chris J. Breisch

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