linux-kernel - Re: [Patch] allow file truncations when both suid and write permissions set

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Date:	Fri, 03 Jul 2009 18:02:50 +0800
From:	Amerigo Wang <amwang@...hat.com>
To:	Eric Paris <eparis@...hat.com>
CC:	Eric Sandeen <sandeen@...hat.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Eugene Teo <eteo@...hat.com>,
	viro@...iv.linux.org.uk
Subject: Re: [Patch] allow file truncations when both suid and write  permissions
 set

Eric Paris wrote:
> On Thu, 2009-07-02 at 18:14 +0800, Amerigo Wang wrote:
>   
>> Eric Paris wrote:
>>     
>>> So NAK on both Amerigo's and Eric's patch.  ATTR_FORCE is wrong.
>>> ATTR_FORCE here is going to force the security system to accept ALL of
>>> the attr changes, not just the ATTR_KILL_SUID and/or ATTR_KILL_SGID you
>>> |= in from should_remove_suid.
>>> You need to follow esandeen's recommendation, change file_remove_suid()
>>> to dentry_remove_suid() and then use dentry_remove_suid() in do_truncate
>>> instead of what you are currently trying to do (and I think that's
>>> supposed to be done under the i_mutex right?)
>>>   
>>>       
>> But file_remove_suid() actually adds ATTR_FORCE too, in __remove_suid()...
>>     
>
> The difference being that it adds it to a private ia_valid that ONLY
> contains the SUID/SGID bits that we need to force the removal of.  Not
> to the ia_valid that contains ATTR_SIZE and ATTR_FILE.
>   

Yeah! Got it. I will prepare a new patch...

Thank you!

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