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From:   Jacob Shivers <jshivers@redhat.com>
Date:   Mon, 4 Jan 2021 11:00:16 -0500
Message-ID: <CALe0_75aeott7xJn0FxSMSANx0AwsxLtjNLC6YZycuE7yN+mGA@mail.gmail.com>
Subject: Re: gssd: set $HOME to prevent recursion when home dirs are on
 kerberized NFS mount revisted
To:     Steve Dickson <SteveD@redhat.com>
Cc:     linux-nfs@vger.kernel.org
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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