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SubjectRe: [PATCH 4.9 038/109] dmaengine: stm32-dma: Fix null pointer dereference in stm32_dma_tx_status
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with Pierre Yves mail it's better ;-)

On 12/07/2017 02:04 PM, Ludovic BARRE wrote:
> add Pierre-yves Mordret
>
> acked-by: Ludovic BARRE <ludovic.barre@st.com>
>
> On 12/07/2017 01:56 PM, Greg Kroah-Hartman wrote:
>> 4.9-stable review patch.  If anyone has any objections, please let me
>> know.
>>
>> ------------------
>>
>> From: M'boumba Cedric Madianga <cedric.madianga@gmail.com>
>>
>>
>> [ Upstream commit 57b5a32135c813f2ab669039fb4ec16b30cb3305 ]
>>
>> chan->desc is always set to NULL when a DMA transfer is complete.
>> As a DMA transfer could be complete during the call of
>> stm32_dma_tx_status,
>> we need to be sure that chan->desc is not NULL before using this variable
>> to avoid a null pointer deference issue.
>>
>> Signed-off-by: M'boumba Cedric Madianga <cedric.madianga@gmail.com>
>> Reviewed-by: Ludovic BARRE <ludovic.barre@st.com>
>> Signed-off-by: Vinod Koul <vinod.koul@intel.com>
>> Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
>> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> ---
>>   drivers/dma/stm32-dma.c |   10 +++-------
>>   1 file changed, 3 insertions(+), 7 deletions(-)
>>
>> --- a/drivers/dma/stm32-dma.c
>> +++ b/drivers/dma/stm32-dma.c
>> @@ -884,7 +884,7 @@ static enum dma_status stm32_dma_tx_stat
>>       struct virt_dma_desc *vdesc;
>>       enum dma_status status;
>>       unsigned long flags;
>> -    u32 residue;
>> +    u32 residue = 0;
>>       status = dma_cookie_status(c, cookie, state);
>>       if ((status == DMA_COMPLETE) || (!state))
>> @@ -892,16 +892,12 @@ static enum dma_status stm32_dma_tx_stat
>>       spin_lock_irqsave(&chan->vchan.lock, flags);
>>       vdesc = vchan_find_desc(&chan->vchan, cookie);
>> -    if (cookie == chan->desc->vdesc.tx.cookie) {
>> +    if (chan->desc && cookie == chan->desc->vdesc.tx.cookie)
>>           residue = stm32_dma_desc_residue(chan, chan->desc,
>>                            chan->next_sg);
>> -    } else if (vdesc) {
>> +    else if (vdesc)
>>           residue = stm32_dma_desc_residue(chan,
>>                            to_stm32_dma_desc(vdesc), 0);
>> -    } else {
>> -        residue = 0;
>> -    }
>> -
>>       dma_set_residue(state, residue);
>>       spin_unlock_irqrestore(&chan->vchan.lock, flags);
>>
>>

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