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From:   Jann Horn <jannh@google.com>
Date:   Mon, 30 Apr 2018 16:15:58 +0200
Message-ID: <CAG48ez3WW49fGaNkG4rd7aFB7HXRKe24Yh_w55JWoG3Cz1HN2A@mail.gmail.com>
Subject: Re: [PATCH v2] inode: debugfs_create_dir uses mode permission from parent
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Kees Cook <keescook@chromium.org>,
        Thomas Richter <tmricht@linux.ibm.com>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        brueckner@linux.vnet.ibm.com,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        kernel list <linux-kernel@vger.kernel.org>
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On Fri, Apr 27, 2018 at 3:49 PM, Greg KH <gregkh@linuxfoundation.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?