dmaengine: stm32-mdma: abort resume if no ongoing transfer

chan->desc can be null, if transfer is terminated when resume is called,
leading to a NULL pointer when retrieving the hwdesc.
To avoid this case, check that chan->desc is not null and channel is
disabled (transfer previously paused or terminated).

Fixes: a4ffb13 ("dmaengine: Add STM32 MDMA driver")
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20231004163531.2864160-1-amelie.delaunay@foss.st.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: ADESTM

drivers/dma/stm32-mdma.c

@@ -1236,6 +1236,10 @@ static int stm32_mdma_resume(struct dma_chan *c)
 	unsigned long flags;
 	u32 status, reg;
 
+	/* Transfer can be terminated */
+	if (!chan->desc || (stm32_mdma_read(dmadev, STM32_MDMA_CCR(chan->id)) & STM32_MDMA_CCR_EN))
+		return -EPERM;
+
 	hwdesc = chan->desc->node[chan->curr_hwdesc].hwdesc;
 
 	spin_lock_irqsave(&chan->vchan.lock, flags);