Re: HPN and None options in OpenSSH

On Mon, Jan 25, 2016 at 12:28:20PM +0100, Jan Bramkamp wrote:

> 
> 
> On 24/01/16 15:50, Dag-Erling Smørgrav wrote:
> > Slawa Olhovchenkov <slw_at_zxy.spb.ru> writes:
> >> Can you do some small discurs about ssh+kerberos?
> >> I am try to use FreeBSD with $HOME over kerberoized NFS.
> >> For kerberoized NFS gssd need to find cache file "called
> >> /tmp/krb5cc_<uid>, where <uid> is the effective uid for the RPC
> >> caller" (from `man gssd`).
> >>
> >> sshd contrary create cache file for received ticket called
> >> /tmp/krb5cc_XXXXXXX (random string, created by krb5_cc_new_unique). Is
> >> this strong security  requirement or [FreeBSD/upstream] can be patched
> >> (or introduce option) to use /tmp/krb5cc_<uid> as cache file for
> >> received ticket?
> >
> > I wasn't aware of that.  It should be easy to patch, but in the
> > meantime, you can try something like this in .bashrc or whatever:
> >
> > krb5cc_uid="/tmp/krb5cc_$(id -u)"
> > if [ -n "${KRB5CCNAME}" -a "${KRB5CCNAME}" != "${krb5ccuid}" ] ; then
> >          if mv "${KRB5CCNAME}" "${krb5ccuid}" ; then
> >                  export KRB5CCNAME="${krb5ccuid}"
> >          else
> >                  echo "Unable to rename krb5 credential cache" >&2
> >          fi
> > fi
> > unset krb5ccuid
> 
> If $KRB5CCNAME is set during PAM session setup than the pam_exec module 
> might allow a reliable implementation along those lines:
> 
>    - Stop if $KRBCCNAME is invalid (klist -t)
>    - Stop if /tmp/krb5cc_$UID is already valid and has enough time left
>    - Copy the ticket to /tmp and rename it to /tmp/krb5cc_$UID.
> 
> Keep in mind that this approach leaves valid tickets in /tmp after the 
> SSH session ends while OpenSSH normally does its best to tie forwarded 
> tickets to a SSH session.

Please check me: you propose to add to /etc/pam.d/sshd string like

session         required        pam_exec.so /patch/to/some/scripts

and do above checks in this scripts?

'session' executed after 'account' phase, on 'account' phase NFS must
be already accessed (for checks presents some files in $HOME and
importing/executing/interpretating, like .login_conf, .k5login and
etc).