linux-kernel - Permission problems - though all three UIDs are 0

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Message-ID: <0236bec1badc3e2cbbcbda6306dfa3d6@cs.uni-dortmund.de>
Date:   Wed, 21 Nov 2018 16:51:50 +0100
From:   Christoph Pleger <christoph.pleger@...uni-dortmund.de>
To:     linux-kernel@...r.kernel.org
Subject: Permission problems  - though all three UIDs are 0

Hello,

I want to ask for the possible reasons why a program, called from 
another program with setuid-root file permissions and an additional 
setreuid(0,0) to also set the real uid to 0, still gets an "Operation   
not permitted" error.

In my case, I execve lvcreate from the setuid-root binary. This works 
well when I use my program as a non-root user from the command line, but 
I want to call it is a non-root user from pam_exec PAM module and with 
that lvcreate fails.

Regards
   Christoph

PS: Please, no discussion about possible security holes in 
setuid-programs here