linux-kernel - Re: debugfs file creation from a user process ioctl

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Message-ID: <20120927151841.GB23895@kroah.com>
Date:	Thu, 27 Sep 2012 08:18:41 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Dave Airlie <airlied@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ben Skeggs <bskeggs@...hat.com>
Subject: Re: debugfs file creation from a user process ioctl

On Thu, Sep 27, 2012 at 02:17:05PM +1000, Dave Airlie wrote:
> Hi guys,
> 
> we've been seeing an error with nouveau and I'm not sure if its new or
> we just never spent time looking into it.
> 
> The basics are when a new drm client opens the device it gets a
> channel assigned, we allocate the channel and a side effect of channel
> allocation is we get a file in debugfs with some info on the channel.
> However this fails as the process context we are in is non-root, and
> the directory is 755.

But the kernel is the thing that is creating the file, so shouldn't it
be created no matter the permission setting?  I guess I never thought of
something other than the "root" process ever creating debugfs files,
odd.

> I don't think I want to be modifiying fsuid, but is there another
> practical way to do this, its not majorly urgent, Ben has indicated
> he's probably ripping the channel debugfs code out but I was just
> wondering for future reference.

I don't think anything other than modifying fsuid would work here,
sorry.  Put it in the "create the debugfs file" function and you should
be fine.

thanks,

greg k-h
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