linux-kernel - Re: [PATCH] vfs: fix IMA lockdep circular locking dependency

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Date:	Wed, 30 May 2012 17:40:54 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Eric Paris <eparis@...isplace.org>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Mimi Zohar <zohar@...ibm.com>,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfs: fix IMA lockdep circular locking dependency

On Wed, May 30, 2012 at 5:28 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> FWIW, I think it's cleaner to take the whole thing into an inlined helper.

Even better.

I notice that your inlined helper doesn't do what I did: if PROT_EXEC
is already set, stop all the stupid games. IOW, the first test in that
function could as well be

    if (prot & (PROT_READ | PROT_EXEC) != PROT_READ)
        return prot;

because if PROT_EXEC is already set, or if PROT_READ wasn't set, none
of the rest of the checks make any sense at all.

But that's just me being anal. It doesn't really *matter* if we end up
setting PROT_EXEC again.

> It can be reorganized a bit, though.  vm_mmap() aside, there are only two
> callers of do_mmap(), both passing it 0 as the last argument.  So let's
> lift these checks on offset into vm_mmap() and kill do_mmap() completely -
> all that remains of it would be a call of do_mmap_pgoff().  And there's no
> reason to put those sanity checks (now in vm_mmap()) under ->mmap_sem,
> of course.  At that point we *do* get 4 identical pieces of code.  Let's
> call that vm_mmap_pgoff() and put it (and vm_mmap()) to mm/util.c.  Voila...

Good.

End result looks fine to me.

             Linus
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