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Date: Fri, 03 Jul 2009 18:02:50 +0800
From: Amerigo Wang <amwang@redhat.com>
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To: Eric Paris <eparis@redhat.com>
CC: Eric Sandeen <sandeen@redhat.com>, linux-kernel@vger.kernel.org,
       akpm@linux-foundation.org, Eugene Teo <eteo@redhat.com>,
       viro@zeniv.linux.org.uk
Subject: Re: [Patch] allow file truncations when both suid and write  permissions
 set
References: <20090625090146.6616.9720.sendpatchset@localhost.localdomain>	 <4A4BA6F8.7090905@redhat.com> <4A4BB898.10909@redhat.com>	 <7e0fb38c0907011229h328c8c48i55df5e234b7d367d@mail.gmail.com>	 <1246479341.22562.71.camel@dhcp235-23.rdu.redhat.com>	 <4A4C887F.2050508@redhat.com> <1246536739.22562.73.camel@dhcp235-23.rdu.redhat.com>
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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!