linux-kernel - Re: [PATCH 1/3] IMA: move read/write counters into struct inode

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Message-ID: <20101019172805.GU19804@ZenIV.linux.org.uk>
Date:	Tue, 19 Oct 2010 18:28:05 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Eric Paris <eparis@...hat.com>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, hch@...radead.org, zohar@...ibm.com,
	warthog9@...nel.org, david@...morbit.com, jmorris@...ei.org,
	kyle@...artin.ca, hpa@...or.com, akpm@...ux-foundation.org,
	mingo@...e.hu
Subject: Re: [PATCH 1/3] IMA: move read/write counters into struct inode

On Tue, Oct 19, 2010 at 10:03:48AM -0700, Linus Torvalds wrote:
> On Tue, Oct 19, 2010 at 9:55 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
> >
> > a) i_writecount is about VM_DENYWRITE, basically. ?Reusing it for ima could
> > get unpleasant; when it's positive, we are fine, but it can get negative as
> > well. ?IMA will have interesting time dealing with that.
> >
> > b) i_count is simply a refcount for struct inode. ?Not exactly the number
> > of dentries, but that's the main contributor. ?Basically, that's "how many
> > pointers outside of inode hash chains point that that struct inode at the
> > moment".
> 
> My question was deeper. More along the lines of "why would IMA care?"
> 
> How/why could IMA ever care about the pointless and trivial
> differences between its current private open/read/write counts and the
> counts that we already maintain?
> 
> Yes, yes, I realize that they have technical differences in what they
> count. That's not the question. The question is "Why would IMA care?"

I'd rather not say what I think about IMA sanity (and usefulness); as for what
it tries to do...  They want to whine if you open a file that is already opened
for write and they want to whine if you open a file for write when it's already
opened for read.  Unless they decide to leave the file alone, that is.
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