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

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Date:	Thu, 13 Mar 2014 10:18:34 +0800
From:	Shuo Liu <shuox.liu@...il.com>
To:	Kees Cook <keescook@...omium.org>
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>,
	"Liu, ShuoX" <shuox.liu@...el.com>
Subject: Re: [PATCH 1/2] pstore: fix buffer overflow while write offset equal
 to buffer size

2014-03-13 0:50 GMT+08:00 Kees Cook <keescook@...omium.org>:
> 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?
Thanks.
We indeed hit it when we enhanced the ramoops tracing.

>
> 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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