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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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