[PATCH AUTOSEL for 4.9 05/54] dmaengine: stm32-dma: Fix null pointer dereference in stm32_dma_tx_status

[alexander.levin@verizon.com]

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>
---
 drivers/dma/stm32-dma.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
index bd758e67843c..ae3f60be7759 100644
--- a/drivers/dma/stm32-dma.c
+++ b/drivers/dma/stm32-dma.c
@@ -884,7 +884,7 @@ static enum dma_status stm32_dma_tx_status(struct dma_chan *c,
 	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_status(struct dma_chan *c,
 
 	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);
-- 
2.11.0