[sudo-users] Strange sudo for root user

[Gerhard Brauer]

Hello,

new on this list; cause I have get noticed on a strange, silly problem
with sudo.
We have a topic on archlinux.de forum where a user of us have this
problem, so it's not me and i could not provide direct information
ASAP.

So here we go:
Fresh archlinux installation (only a base system, bash TTY login).
User login after reboot as root, install sudo version:
1.7.4.p4-1 (i686)

Then (still as root) he does a:
sudo ls
and get:
---
can't open /etc/sudoers: Keine Berechtigung  (<--- This means
permission denied)
sudo: no valid sudoers sources found,quitting
---

The /etc/sudoers at this time has the only *active* line:
root ALL=(ALL) ALL)

Of course he could do without problem a:
cat /etc/sudoers
as root.

/usr/bin/sudo has
4755 root.root
/etc/sudoers
0440 root.root

There is no ACL or ATTR on etc/sudoers which pervent from opening.
I advise him to do a strace, but the trace only shows that sudoers
could not be opened O_RDONLY
(Full trace could be found here: http://pastebin.com/Kbt5b2G2)

His root account could do visudo without problems, also a visudo -sc
shows no syntax errors.

I never have seen this behavior all the years, and i'm out of ideas.
He has done the install twice, with the same result. But our sudo
package is ok, no other user have this problem. I have compared with
him the md5sum's of the sudo binary, also ok.

He tries this on a normal laptop, no VM,XEN or similar. Filesystem
he uses is ext3 with no nosuid option or similar. No automounter, no
NFS,...  But something in his environment must be very special to
run twice in this error.

Have i said that I'm out of ideas what to test further? ;-)
IMHO the only possibility is thar sudo isn't started setuid, but the
flags are ok and he does this as root(uid 0).

Have you any ideas what could be the reason? Or what to test?

Regards
        Gerhard

PS: for german speaker the forum post is here:
https://bbs.archlinux.de/viewtopic.php?id=17941