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

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Message-Id: <20171026083449.57ccb533@mschwideX1>
Date:   Thu, 26 Oct 2017 08:34:49 +0200
From:   Martin Schwidefsky <schwidefsky@...ibm.com>
To:     Elena Reshetova <elena.reshetova@...el.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        heiko.carstens@...ibm.com, jwi@...ux.vnet.ibm.com,
        ubraun@...ux.vnet.ibm.com, peterz@...radead.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.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.