[PATCH v1 1/6] dmaengine: switchtec-dma: fix double-free in switchtec_dma_free_desc()

[Logan Gunthorpe <logang@deltatee.com>]

switchtec_dma_free_desc() frees swdma_chan->hw_sq, hw_cq, and every
desc_ring[] entry without clearing the pointers afterward. If
switchtec_dma_alloc_chan_resources() fails partway through and calls
it during unwind, then a later retry of alloc_chan_resources() fails
in switchtec_dma_alloc_desc() before reallocating one of those
pointers, its own failure path calls switchtec_dma_free_desc() again
and frees the same, already-freed pointers a second time.

NULL out each pointer as it's freed so a subsequent call is a no-op
for anything already released.

Fixes: 30eba9df76ad ("dmaengine: switchtec-dma: Implement hardware initialization and cleanup")
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 drivers/dma/switchtec_dma.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/switchtec_dma.c b/drivers/dma/switchtec_dma.c
index 3ef928640615..a4a7d66d042d 100644
--- a/drivers/dma/switchtec_dma.c
+++ b/drivers/dma/switchtec_dma.c
@@ -886,14 +886,18 @@ static void switchtec_dma_free_desc(struct switchtec_dma_chan *swdma_chan)
 	if (swdma_chan->hw_sq)
 		dma_free_coherent(swdma_dev->dma_dev.dev, size,
 				  swdma_chan->hw_sq, swdma_chan->dma_addr_sq);
+	swdma_chan->hw_sq = NULL;
 
 	size = SWITCHTEC_DMA_CQ_SIZE * sizeof(*swdma_chan->hw_cq);
 	if (swdma_chan->hw_cq)
 		dma_free_coherent(swdma_dev->dma_dev.dev, size,
 				  swdma_chan->hw_cq, swdma_chan->dma_addr_cq);
+	swdma_chan->hw_cq = NULL;
 
-	for (i = 0; i < SWITCHTEC_DMA_RING_SIZE; i++)
+	for (i = 0; i < SWITCHTEC_DMA_RING_SIZE; i++) {
 		kfree(swdma_chan->desc_ring[i]);
+		swdma_chan->desc_ring[i] = NULL;
+	}
 }
 
 static int switchtec_dma_alloc_desc(struct switchtec_dma_chan *swdma_chan)
-- 
2.47.3