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

[Shuo Liu]

2014-03-13 0:50 GMT+08:00 Kees Cook <keescook@xxxxxxxxxxxx>:
> On Wed, Mar 12, 2014 at 6:24 AM, Liu Shuo <shuox.liu@xxxxxxxxx> wrote:
>> From: Liu ShuoX <shuox.liu@xxxxxxxxx>
>>
>> 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@xxxxxxxxx>
>
> 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@xxxxxxxxxxxx>
>
> -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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/