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From:   Jacob Shivers <jshivers@redhat.com>
Date:   Mon, 23 Nov 2020 13:17:05 -0500
Message-ID: <CALe0_74eB89Koni0i14aB=2CSitzg1WkRihe7KZGDJ5OoPSahw@mail.gmail.com>
Subject: gssd: set $HOME to prevent recursion when home dirs are on kerberized
 NFS mount revisted
To:     linux-nfs@vger.kernel.org
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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.

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 */

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.

Does anyone consider adding the above proposed flag as being problematic?