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Re: admin privileges when logging in by ssh?

On Oct  4 11:59, Andrew Schulman wrote:
> > On Sep 12 10:24, Andrew Schulman wrote:
> > > > When a user with administrative privileges logs in to sshd, it seems that the user is only granted
> > > > standard user privileges for that session.  Is there a way around that?  How can I get the admin
> > > > privileges for that session?
> > > 
> > > Winding this up:
> > > 
> > > Password authentication to sshd is all that's needed to be granted the account's admin privileges on
> > > login.  I was mistaken about UAC:  unlike at the console, when you log in by ssh, the account's
> > > admin privileges are granted at login, without needing any further authentication to UAC.
> > 
> > I'm quite puzzeled since password authentication should not be needed.
> > This should work with pubkey as well.  Please see
> > for
> > a discussion how setuid works in Cygwin.
> > 
> > In all cases, password auth and passwordless auth, you should get a full
> > admin token.  In case of password auth and in the passwordless methods
> > 2 and 3, the OS returns a restricted token under UAC, but that token
> > has a reference to the full admin token attached.  Cygwin fetches this
> > token and uses that when switching the user context.  In the default
> > passwordless method 1, Cygwin creates a token from scratch, which also
> > has full admin rights.  However, this token has a couple of problems as
> > described in
> > Probably that's what you stumble over.
> Thanks for writing up that documentation of user context switching (I
> assume it was you who wrote it).  It's complex.

Sorry, but the Windows authentication stuff is complex.

> So IIUC, sshd by default uses method 1, creating a token from scratch.  So

Not sshd in the first place, but the underlying set(e)uid system call.

> when a user logs in with pubkey authentication, they won't have a logon
> session, which means their SID name may be misidentified by native Windows
> apps; and they won't have access to password-protected network shares.  But
> they should still have all of the privileges normally granted to their
> account.

Right.  And in contrast to the normal user token, the token hand-crafted
by Cygwin has all privileges enabled by default.  But it suffers from
the fact that there's no login session attached to it.  Don't ask.  This
part of the authentication mechanism I don't understand and afaics it's
not documented at all.

> I'm not able to test it right now, but what I observed before was that when
> a user with the SeBackupPrivilege and SeBackupPrivilege privileges logged
> in by password authentication, it could use those privileges (with rsync);
> but when it logged in by pubkey authentication, it couldn't.  So I agree
> that this is puzzling since it doesn't seem to square with the description
> above.  This is on Windows 7 Home Premium.

The OS shouldn't matter.

> I'll test this again when I can, to be sure what I observed is correct.  If
> you can suggest any diagnostic tools to help identify the available
> privileges, that would be helpful.

Does Windows 7 Home Premium come with a native whoami?  I'm only
running Ultimate, which has this tool:

  $ /cygdrive/c/Windows/System32/whoami /all

With method 1 you will see a wrong user name showing up, even though
the user SID is correct.

If you don't have a native whoami, I hacked some tool once which I
use all the time to do basically the same as the Windows whoami.
I attached the ugly source code, build with

  $ g++ -o gettokinfo

and run from the session you want to check like this

  $ ./gettokinfo

if you don't want to see the privileges, or like this

  $ ./gettokinfo x

if you want to see them.


Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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