linux-kernel - Re: [PATCH v3 1/1] vfs: iversion truncate bug fix

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Date:	Wed, 04 Jan 2012 23:17:12 -0500
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Greg KH <greg@...ah.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitry Kasatkin <dmitry.kasatkin@...el.com>,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] vfs: iversion truncate bug fix

On Wed, 2012-01-04 at 18:06 -0800, Greg KH wrote:
> On Wed, Jan 04, 2012 at 04:46:38PM -0800, Andrew Morton wrote:
> > On Wed, 04 Jan 2012 19:33:49 -0500
> > Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
> > 
> > > On Wed, 2012-01-04 at 15:28 -0800, Andrew Morton wrote:
> > > > On Thu, 22 Dec 2011 08:26:30 -0500
> > > > Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
> > > > 
> > > > > On Thu, 2011-12-22 at 12:54 +0200, Dmitry Kasatkin wrote:
> > > > > > When a file is truncated with truncate()/ftruncate() and then closed,
> > > > > > iversion is not updated. This patch uses ATTR_SIZE flag as an indication
> > > > > > to increment iversion.
> > > > > > 
> > > > > > Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@...el.com>
> > > > > 
> > > > > Acked-by: Mimi Zohar <zohar@...ibm.com> 
> > > > > (Stable should be cc'ed on this patch.)
> > > > 
> > > > why?
> > > 
> > > Why backported?
> > 
> > Yes.  If you want to submit the patch to the -stable maintainer then
> > you should explain to him why the fix is important enough to warrant
> > doing that.  That involves explaining the user-visible effects of
> > the bug.
> > 
> > >  The IMA measurement list could be incomplete.
> > 
> > In more detail than this.  Maybe he knows what the above sentence
> > means, but I sure don't.
> 
> Nope, I don't either :)

On fput(), i_version is used to detect and flag files that have changed
and need to be re-measured in the IMA measurement policy.  When a file
is truncated with truncate()/ftruncate() and then closed, i_version is
not updated.  As a result, although the file has changed, it will not be
re-measured and added to the IMA measurement list on subsequent access.

Mimi

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