Sudo does not work in chroot

Question

I would like to be able to use the sudo command in a chroot environment.

I start the chroot as follows:

chroot /debian-squeeze /bin/bash

Now I'm logged in as root in the chroot. I can do su user to log in as a user named user. Now, sudo does not work:

user@HD:/$ sudo ls
sudo: must be setuid root

Some diagnostics:

user@HD:/$ which sudo
/usr/bin/sudo

user@HD:/$ ls -al /usr/bin/sudo
-rwsr-xr-x 2 root root 143884 May 23  2012 /usr/bin/sudo

user@HD:/$ ls -aln /usr/bin/sudo
-rwsr-xr-x 2 0 0 143884 May 23  2012 /usr/bin/sudo

root@HD:/# cat /etc/sudoers
Defaults    env_reset
root    ALL=(ALL) ALL
user ALL=(ALL) ALL
%sudo ALL=(ALL) ALL

As root, I can execute sudo without error.

Can anyone explain me why sudo (or setuid) does not work like this?

Answer 1

My guess is that /debian-squeeze is on a separate filesystem mounted without defaults or suid. The kernel will ignore the setuid bit on filesystems mounted without suid (defaults implies suid). To fix it:

mount -o remount,suid /debian-squeeze