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

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Message-Id: <1246536739.22562.73.camel@dhcp235-23.rdu.redhat.com>
Date:	Thu, 02 Jul 2009 08:12:19 -0400
From:	Eric Paris <eparis@...hat.com>
To:	Amerigo Wang <amwang@...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

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.

-Eric

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