linux-kernel - Re: [PATCH 1/2] pstore: fix buffer overflow while write offset equal to buffer size

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Date:	Wed, 12 Mar 2014 09:50:33 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Liu Shuo <shuox.liu@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Anton Vorontsov <anton@...msg.org>,
	Colin Cross <ccross@...roid.com>,
	Tony Luck <tony.luck@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>
Subject: Re: [PATCH 1/2] pstore: fix buffer overflow while write offset equal
 to buffer size

On Wed, Mar 12, 2014 at 6:24 AM, Liu Shuo <shuox.liu@...il.com> wrote:
> From: Liu ShuoX <shuox.liu@...el.com>
>
> In case new offset is equal to prz->buffer_size, it won't wrap at this
> time and will return old(overflow) value next time.
>
> Signed-off-by: Liu ShuoX <shuox.liu@...el.com>

This seems correct; good catch. Have you seen this problem happen, or
is this just from reading the code?

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
> fs/pstore/ram_core.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
> index de272d4..ff7e3d4 100644
> --- a/fs/pstore/ram_core.c
> +++ b/fs/pstore/ram_core.c
> @@ -54,7 +54,7 @@ static size_t buffer_start_add_atomic(struct
> persistent_ram_zone *prz, size_t a)
>         do {
>                 old = atomic_read(&prz->buffer->start);
>                 new = old + a;
> -               while (unlikely(new > prz->buffer_size))
> +               while (unlikely(new >= prz->buffer_size))
>                         new -= prz->buffer_size;
>         } while (atomic_cmpxchg(&prz->buffer->start, old, new) != old);
>
> @@ -91,7 +91,7 @@ static size_t buffer_start_add_locked(struct
> persistent_ram_zone *prz, size_t a)
>
>         old = atomic_read(&prz->buffer->start);
>         new = old + a;
> -       while (unlikely(new > prz->buffer_size))
> +       while (unlikely(new >= prz->buffer_size))
>                 new -= prz->buffer_size;
>         atomic_set(&prz->buffer->start, new);
>
> --
> 1.8.3.2
>
>
>



-- 
Kees Cook
Chrome OS Security
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