linux-kernel - RE: [PATCH 1/3] [S390] vmur: convert urdev.ref_count from atomic_t to refcount

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Date:   Fri, 27 Oct 2017 06:35:35 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     Martin Schwidefsky <schwidefsky@...ibm.com>
CC:     "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>,
        "jwi@...ux.vnet.ibm.com" <jwi@...ux.vnet.ibm.com>,
        "ubraun@...ux.vnet.ibm.com" <ubraun@...ux.vnet.ibm.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>
Subject: RE: [PATCH 1/3] [S390] vmur: convert urdev.ref_count from atomic_t
 to refcount_t


> On Fri, 20 Oct 2017 10:47:48 +0300
> Elena Reshetova <elena.reshetova@...el.com> 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 urdev.ref_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>
> 
> Added to s390/linux:features for the next merge window. Thanks.

Thank you very much!

Best Regards,
Elena.
> 
> --
> blue skies,
>    Martin.
> 
> "Reality continues to ruin my life." - Calvin.