linux-kernel - Re: debugfs & vfs file permission issue?

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Date:	Tue, 6 Jan 2009 00:54:58 -0500
From:	"Mike Frysinger" <vapier.adi@...il.com>
To:	"Greg KH" <gregkh@...e.de>
Cc:	"Robin Getz" <rgetz@...ckfin.uclinux.org>, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: debugfs & vfs file permission issue?

On Tue, Jan 6, 2009 at 00:48, Greg KH wrote:
> On Mon, Jan 05, 2009 at 09:57:07PM -0500, Robin Getz wrote:
>> On 2.6.28-rc2, If I create a debugfs file with
>>
>>     debugfs_create_x16("SPORT1_TX", 0200 , parent, 0xFFC00910);
>
> Um, are you are passing in a pointer to a known memory location
> properly?  Why would it be ok for the kernel to directly read that
> location?

it's a nommu system and the 0xffc00000+ addresses are always available

>> Although the file shows up as write only (no read):
>>
>> root:/> ls -l /sys/kernel/debug/blackfin/SPORT/SPORT1_TX
>> --w-------    1 root     root            0 Jan  1
>> 2007 /sys/kernel/debug/blackfin/SPORT/SPORT1_TX
>>
>> root:/> cat /sys/kernel/debug/blackfin/SPORT/SPORT1_TX
>>
>> Still works - and causes the read to occur, which crashes :(
>
> You're root, you can do anything :)

any thoughts on how to declare debugfs files that are read or write
only ?  we'll have to add new helper functions or have it be a
parameter or declare our own debugfs file ?
-mike
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