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From:   David Wysochanski <dwysocha@redhat.com>
Date:   Mon, 1 Mar 2021 13:54:03 -0500
Message-ID: <CALF+zOndUvphHGvvUmJwRaGE8-E6c8zdiGja0WBX1JKt9BCudg@mail.gmail.com>
Subject: Re: gssd: set $HOME to prevent recursion when home dirs are on
 kerberized NFS mount revisted
To:     Jacob Shivers <jshivers@redhat.com>
Cc:     Steve Dickson <SteveD@redhat.com>,
        linux-nfs <linux-nfs@vger.kernel.org>
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Precedence: bulk

I was talking to Jake and I think he will submit this again without
attachments so it's a little easier to review.

On Mon, Mar 1, 2021 at 12:07 PM Jacob Shivers <jshivers@redhat.com> wrote:
>
> Patches that include a '-H' flag and man page entry.
>
> The default is to maintain behavior since
> 2f682f25c642fcfe7c511d04bc9d67e732282348, but passing '-H' avoids
> $HOME being set to '/'.
> Also included a patch for /etc/nfs.conf to add 'set-home=1'. Setting
> it to false is equivalent to passing '-H' to rpc.gssd.
>
> Regards,
>
> Jacob Shivers
>
> On Mon, Jan 4, 2021 at 11:00 AM Jacob Shivers <jshivers@redhat.com> wrote:
> >
> > Hello,
> >
> > I completely missed this so please excuse the delay.
> >
> > > On 11/23/20 1:17 PM, Jacob Shivers wrote:
> > > > Commit 2f682f25c642fcfe7c511d04bc9d67e732282348 changed existing
> > > > behavior to avoid a deadlock for users using Kerberized NFS home dirs.
> > > >
> > > > However, this also prevents users leveraging their own k5identity
> > > > files under their home directory and instead rpc.gssd uses a
> > > > system-wide /.k5identity file. For users expecting to use their own
> > > > k5identity file this is certainly unexpected.
> > > So how is the deadlock not happening when ~/.k5identity is on a NFS
> > > home directory? What am I missing?
> > They are not using NFS for home directories. They are accessing
> > systems with a local fs backing the /home
> >
> > > > Below is some pseudo code that was proposed and would just add a flag
> > > > allowing for the behavior prior to
> > > > 2f682f25c642fcfe7c511d04bc9d67e732282348:
> > > >
> > > > /* psudo code snippet starts here */
> > > >         /*
> > > >          * Some krb5 routines try to scrape info out of files in the user's
> > > >          * home directory. This can easily deadlock when that homedir is on a
> > > > -        * kerberized NFS mount. By setting $HOME unconditionally to "/", we
> > > > +        * kerberized NFS mount. Some users may not have $HOME on NFS.
> > > > +        * By default setting $HOME unconditionally to "/", we
> > > >          * prevent this behavior in routines that use $HOME in preference to
> > > >          * the results of getpw*.
> > > > +        * Users who have $HOME on krb5-NFS should set
> > > > `--home-not-kerberized` in argv
> > > > +        * Users who have $HOME on krb5-NFS but want to use their
> > > > $HOME anyway should set NFS_HOME_ACCESSIBLE=TRUE
> > > >          */
> > > > +       if (argv == '--home-not-kerberized') ||
> > > > (getenv("NFS_HOME_ACCESSIBLE") == 'TRUE') {
> > > > +               log.debug('Not masking $HOME, this breaks on Kerberized $HOME');
> > > > +       }
> > > > +       else {
> > > > +               log.debug('Assuming $HOME requires Kerberos, use
> > > > `--home-not-kerberized` to change this behavior');
> > > >         if (setenv("HOME", "/", 1)) {
> > > >                 printerr(1, "Unable to set $HOME: %s\n", strerror(errn));
> > > >                 exit(1);
> > > >         }
> > > > +       }
> > > > /* psudo code snippet ends here */
> > > In general I'm pretty reluctant to add flags but what is needed
> > > to do so is a company single letter flag '-H' and a man page
> > > entry describing the flag.
> > Ok.
> >
> > > >
> > > > While acknowledging the use of this flag for Kerberized NFS home dirs
> > > > is undesirable and would cause a deadlock, there should be no issue
> > > > for users not using Kerberized NFS home dirs.
> > > What apps are you using that is seeing this problem?
> > It is just when accessing the Kerberized NFS share. Other Kerberos
> > aware services/applications check for the existence of ~/.k5identify
> > before reading /var/kerberos/krb5/user/${EUID}/client.keytab. rpc.gssd
> > no longer does this and the intent of the patch would be to add
> > granularity to choose the behavior or rpc.gssd with respect to
> > scanning for a k5identity file.
> >
> > If any additional information is required, please inform me.
> >
> > Thanks,
> >
> > Jacob Shivers