linux-kernel - Re: [PATCH v2] inode: debugfs_create_dir uses mode permission from parent

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Date:   Mon, 30 Apr 2018 07:26:43 -0700
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        brueckner@...ux.vnet.ibm.com,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] inode: debugfs_create_dir uses mode permission from
 parent

On Mon, Apr 30, 2018 at 04:15:58PM +0200, Jann Horn wrote:
> On Fri, Apr 27, 2018 at 3:49 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
> > I'm going to add Kees and the kernel-hardning list here, as I'd like
> > their opinions for the patch below.
> >
> > Kees, do you have any problems with this patch?  I know you worked on
> > making debugfs more "secure" from non-root users, this should still keep
> > the intial mount permissions all fine, right?  Anything I'm not
> > considering here?
> >
> > thanks,
> >
> > greg k-h
> >
> > On Fri, Apr 27, 2018 at 02:35:47PM +0200, Thomas Richter wrote:
> >> Currently function debugfs_create_dir() creates a new
> >> directory in the debugfs (usually mounted /sys/kernel/debug)
> >> with permission rwxr-xr-x. This is hard coded.
> >>
> >> Change this to use the parent directory permission.
> 
> AFAICS no inodes in debugfs have handlers for the ->rename, ->mkdir,
> ->create inode ops. What is write permission on debugfs directories
> useful for?

I doubt anything :)