[patch] rc.d/tmp (silly mkdir usage)

[Giorgos Keramidas]

On 2005-08-02 09:29, Vasil Dimov <vd at datamax.bg> wrote:
> > --- /etc/rc.d/tmp.orig  Mon Aug  1 23:20:24 2005
> > +++ /etc/rc.d/tmp       Mon Aug  1 23:22:07 2005
> > @@ -48,8 +48,8 @@
> >  [Nn][Oo])
> >         ;;
> >  *)
> > -       if (/bin/mkdir -p /tmp/.diskless 2> /dev/null); then
> > -               rmdir /tmp/.diskless
> > +       if ( > /tmp/.diskless 2> /dev/null); then
> > +               rm /tmp/.diskless
> >         else
> >                 if [ -h /tmp ]; then
> >                         echo "*** /tmp is a symlink to a non-writable area!"
>
> The thing you suggest is bloody insecure. Just imagine some baduser
> doing ln -s /etc/passwd /tmp/.diskless before rc.d/tmp gets executed.
> I guess this is the reason why directory creation is used instead of
> file creation.
>
> I just wonder why a new shell is forked for this test. Simply if
> /bin/mkdir -p /tmp/.diskless 2> /dev/null ; then would do the same
> thing without forking a new shell that only executes /bin/mkdir

I think it's because the current shell is allowed to exit if a command
fails while a conditional test like this is run:

	if mkdir /tmp/foo; then
		echo foo
		rmdir /tmp/foo
	fi

and mkdir may fail.