Re: chmod of generated grub.cfg

[Robert Millan]

On Sun, Sep 06, 2009 at 04:58:40PM +0200, Felix Zielcke wrote:
> 
> Ok here's now a patch.
> Robert do you think this can go into 1.97?

For 1.97 I'd be more comfortable with a simple s/444/400/.  An automated check
smells like it could have corner cases.  In fact I found one:

> @@ -260,6 +260,11 @@ for i in ${grub_mkconfig_dir}/* ; do
>    esac
>  done
>  
> +if [ "x${grub_cfg}" != "x" ] && grep -q "^password " ${grub_cfg}.new ; then
> +  chmod 400 ${grub_cfg}.new || grub_warn "Could not make ${grub_cfg}.new 
> readable by only root.\
> +  This means your password is readable by everyone"
> +fi

There's a short time window in which /boot/grub/grub.cfg.new exists, has been
fully generated, and its mode is 444 rather than 400.  An attacker could poll
this file and with some luck extract a password from it.

-- 
Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."