linux-kernel - Re: [PATCH 1/2] debugfs: Only clobber mode/uid/gid on remount if asked

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Date:   Thu, 1 Sep 2022 17:58:14 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] debugfs: Only clobber mode/uid/gid on remount if
 asked

On Fri, Aug 26, 2022 at 05:44:16PM -0700, Brian Norris wrote:
> Users may have explicitly configured their debugfs permissions; we
> shouldn't overwrite those just because a second mount appeared.

What userspace mounts debugfs twice?

> Only clobber if the options were provided at mount time.
> 
>   # Don't change /sys/kernel/debug/ permissions.
>   mount -t debugfs none /mnt/foo
> 
>   # Change /sys/kernel/debug/ mode and uid, but not gid.
>   mount -t debugfs -o uid=bar,mode=0750 none /mnt/baz

So what happens today with this change?  Without it?

> 
> Signed-off-by: Brian Norris <briannorris@...omium.org>
> ---
> I'm open to writing an LTP test case for this, if that seems like a good
> idea.

If it's really needed, again, why would debugfs be ever mounted more
than once?

thanks,

greg k-h