linux-kernel - Re: [PATCH 02/11] persistent_ram: Fix buffer size clamping during writes

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Date:	Sun, 13 May 2012 20:23:58 -0700
From:	Colin Cross <ccross@...roid.com>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kees Cook <keescook@...omium.org>,
	Arnd Bergmann <arnd@...db.de>,
	John Stultz <john.stultz@...aro.org>, arve@...roid.com,
	Rebecca Schultz Zavin <rebecca@...roid.com>,
	Jesper Juhl <jj@...osbits.net>,
	Randy Dunlap <rdunlap@...otime.net>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Thomas Meyer <thomas@...3r.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marco Stornelli <marco.stornelli@...il.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	kernel-team@...roid.com
Subject: Re: [PATCH 02/11] persistent_ram: Fix buffer size clamping during writes

On Fri, May 11, 2012 at 5:17 PM, Anton Vorontsov
<anton.vorontsov@...aro.org> wrote:
> This is a longstanding bug, almost unnoticeable when calling
> persistent_ram_write() for small buffers.
>
> But when called for large data buffers, the write routine behaves
> incorrectly, as the size may never update: instead of clamping
> the size to the maximum buffer size, buffer_size_add_clamp() returns
> an error (which is never checked by the write routine, btw).
>
> To fix this, we now use buffer_size_add() that actually clamps the
> size to the max value.
>
> Also remove buffer_size_add_clamp(), it is no longer needed.
>
> Signed-off-by: Anton Vorontsov <anton.vorontsov@...aro.org>
> ---
>  drivers/staging/android/persistent_ram.c |   19 +------------------
>  1 file changed, 1 insertion(+), 18 deletions(-)
>
> diff --git a/drivers/staging/android/persistent_ram.c b/drivers/staging/android/persistent_ram.c
> index 12444fd..13a12bc 100644
> --- a/drivers/staging/android/persistent_ram.c
> +++ b/drivers/staging/android/persistent_ram.c
> @@ -79,23 +79,6 @@ static inline void buffer_size_add(struct persistent_ram_zone *prz, size_t a)
>        } while (atomic_cmpxchg(&prz->buffer->size, old, new) != old);
>  }
>
> -/* increase the size counter, retuning an error if it hits the max size */
> -static inline ssize_t buffer_size_add_clamp(struct persistent_ram_zone *prz,
> -       size_t a)
> -{
> -       size_t old;
> -       size_t new;
> -
> -       do {
> -               old = atomic_read(&prz->buffer->size);
> -               new = old + a;
> -               if (new > prz->buffer_size)
> -                       return -ENOMEM;
> -       } while (atomic_cmpxchg(&prz->buffer->size, old, new) != old);
> -
> -       return 0;
> -}
> -
>  static void notrace persistent_ram_encode_rs8(struct persistent_ram_zone *prz,
>        uint8_t *data, size_t len, uint8_t *ecc)
>  {
> @@ -300,7 +283,7 @@ int notrace persistent_ram_write(struct persistent_ram_zone *prz,
>                c = prz->buffer_size;
>        }
>
> -       buffer_size_add_clamp(prz, c);
> +       buffer_size_add(prz, c);
>
>        start = buffer_start_add(prz, c);
>
> --
> 1.7.9.2
>

Acked-by: Colin Cross <ccross@...roid.com>

This is a bug fix for a bug introduced in 3.4-rc1, it should go into
3.4 if there is another rc.
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