Esteemed monks,

I have run into a peculiarity when using the $> variable to demote privileges in one of my programs, which can be simplified to:


sub DropPriv($uid,$groups) {
  $) = $groups;
  $> = $uid;

  if ($> != $uid) {
    print STDERR "demotion to $uid failed, EUID=$>.\n";
    return 0;
  }
  return 1;
}

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This tested fine on my Linux system, the idea being that I would demote myself to nobody (uid 65534) before doing some system calls.

The same code unexpectedly failed on my AIX system with a resulting EUID=-2, which I'm now guessing to be related to an overflow problem since the only difference on AIX is that nobody's uid is 4294967294 by default. When I use a user with a lower uid it works fine.

The AIX system is running v5.8.0, but I got the same result on v5.8.8.

My workaround was to use the "sys" user (uid=3), but can anyone confirm this as an overflow issue with the built-in $> variable and perhaps an alternative solution?

Niel

In reply to EUID cannot be set by 0xbeef

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