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

[Jann Horn]

On Fri, Apr 27, 2018 at 3:49 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 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?