linux-kernel - RE: [PATCH 1/4] bcache: convert cached_dev.count from atomic_t to refcount

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Date:   Mon, 23 Oct 2017 06:45:09 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     Michael Lyle <mlyle@...e.org>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>
CC:     "linux-bcache@...r.kernel.org" <linux-bcache@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
        "kent.overstreet@...il.com" <kent.overstreet@...il.com>,
        "koverstreet@...gle.com" <koverstreet@...gle.com>,
        "ejt@...hat.comg" <ejt@...hat.comg>,
        "snitzer@...hat.com" <snitzer@...hat.com>,
        "shli@...nel.org" <shli@...nel.org>,
        "agk@...hat.com" <agk@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>
Subject: RE: [PATCH 1/4] bcache: convert cached_dev.count from atomic_t to
 refcount_t

> On 10/20/2017 12:37 AM, Elena Reshetova wrote:
> > atomic_t variables are currently used to implement reference
> > counters with the following properties:
> >  - counter is initialized to 1 using atomic_set()
> >  - a resource is freed upon counter reaching zero
> >  - once counter reaches zero, its further
> >    increments aren't allowed
> >  - counter schema uses basic atomic operations
> >    (set, inc, inc_not_zero, dec_and_test, etc.)
> >
> > Such atomic variables should be converted to a newly provided
> > refcount_t type and API that prevents accidental counter overflows
> > and underflows. This is important since overflows and underflows
> > can lead to use-after-free situation and be exploitable.
> >
> > The variable cached_dev.count is used as pure reference counter.
> > Convert it to refcount_t and fix up the operations.
> >
> > Suggested-by: Kees Cook <keescook@...omium.org>
> > Reviewed-by: David Windsor <dwindsor@...il.com>
> > Reviewed-by: Hans Liljestrand <ishkamiel@...il.com>
> > Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> 
> Reviewed-by: Michael Lyle <mlyle@...e.org>
> 
> Thanks for this-- I'm including it in my tree for possible inclusion in
> 4.15 (I've already sent my main chunk of changes upwards).

Thank you Mike! I am dropping then this patch from my list of maintained
conversions. 

Best Regards,
Elena.
> 
> Mike