Re: [PATCH] dmaengine: do not allow access outside of unmap_pool

[Xulin Sun]

>On Tue, May 17, 2016 at 01:00:46PM +0100, Colin King wrote:
>> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>>
>> When CONFIG_DMA_ENGINE_RAID is defined, unmap_pool[] is just 1
>> element in size, however, allows orders of 2..8 to access
>> outside unmap_pool and returns an invalid address. Ensure
>> we fall into the default path and report a BUG() when
>> CONFIG_DMA_ENGINE_RAID is defined and order is out of range.
>>
>> Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>> ---
>>  drivers/dma/dmaengine.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
>> index 8c9f45f..6027e66 100644
>> --- a/drivers/dma/dmaengine.c
>> +++ b/drivers/dma/dmaengine.c
>> @@ -1100,12 +1100,14 @@ static struct dmaengine_unmap_pool 
*__get_unmap_pool(int nr)
>>      switch (order) {
>>      case 0 ... 1:
>>          return &unmap_pool[0];
>> +    #if IS_ENABLED(CONFIG_DMA_ENGINE_RAID)

>Okay if CONFIG_DMA_ENGINE_RAID is enabled (m or y) then IS_ENABLED
>return 1, so we will go inside and not fall into default. And I though
>by changelog that you want it to go to default in CONFIG_DMA_ENGINE_RAID
>is defined!

>What did I miss...

Here it should be when CONFIG_DMA_ENGINE_RAID is NOT defined, 
unmap_pool[] is just 1
element in size,  and the function "__get_unmap_pool" will access 
outside of the array unmap_pool[]
in case orders of 2..8 and returns an invalid address, and I encountered 
the issue.

I think the patch is needed to avoid visiting outside of the array 
unmap_pool[] if CONFIG_DMA_ENGINE_RAID is NOT defined.

Thanks
Xulin
>>      case 2 ... 4:
>>          return &unmap_pool[1];
>>      case 5 ... 7:
>>          return &unmap_pool[2];
>>      case 8:
>>          return &unmap_pool[3];
>> +    #endif
>>      default:
>>          BUG();
>>          return NULL;
>> --
>> 2.8.1
>>