[PATCH v2] dmaengine: sun6i-dma: Fix use-after-free in error handling paths

[Hongling Zeng]

In error handling paths, the for loop frees v_lli in the loop body,
then accesses v_lli->v_lli_next and v_lli->p_lli_next in the
increment expression, which is use-after-free.

Fix by saving both the next virtual and physical pointers before
freeing the current node.

Fixes: 555859308723 ("dmaengine: Add driver for Allwinner sun6i DMA")
Signed-off-by: Hongling Zeng <zenghongling at kylinos.cn>
Suggested-by: Jernej Skrabec <jernej.skrabec at gmail.com>

---
Changes in v2:
 -Refactored the fix to avoid code duplication by creating a helper function
  sun6i_dma_free_lli_list() that handles LLI list cleanup
 -Add Suggested-by: Jernej Skrabec <jernej.skrabec at gmail.com>
---
 drivers/dma/sun6i-dma.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
index a9a254dbf8cb..02dd07001d5a 100644
--- a/drivers/dma/sun6i-dma.c
+++ b/drivers/dma/sun6i-dma.c
@@ -406,16 +406,12 @@ static inline void sun6i_dma_dump_lli(struct sun6i_vchan *vchan,
 		v_lli->len, v_lli->para, v_lli->p_lli_next);
 }
 
-static void sun6i_dma_free_desc(struct virt_dma_desc *vd)
+static void sun6i_dma_free_lli_list(struct sun6i_dma_dev *sdev,
+					struct sun6i_desc *txd)
 {
-	struct sun6i_desc *txd = to_sun6i_desc(&vd->tx);
-	struct sun6i_dma_dev *sdev = to_sun6i_dma_dev(vd->tx.chan->device);
 	struct sun6i_dma_lli *v_lli, *v_next;
 	dma_addr_t p_lli, p_next;
 
-	if (unlikely(!txd))
-		return;
-
 	p_lli = txd->p_lli;
 	v_lli = txd->v_lli;
 
@@ -428,7 +424,17 @@ static void sun6i_dma_free_desc(struct virt_dma_desc *vd)
 		v_lli = v_next;
 		p_lli = p_next;
 	}
+}
 
+static void sun6i_dma_free_desc(struct virt_dma_desc *vd)
+{
+	struct sun6i_desc *txd = to_sun6i_desc(&vd->tx);
+	struct sun6i_dma_dev *sdev = to_sun6i_dma_dev(vd->tx.chan->device);
+
+	if (unlikely(!txd))
+		return;
+
+	sun6i_dma_free_lli_list(sdev, txd);
 	kfree(txd);
 }
 
@@ -788,9 +794,7 @@ static struct dma_async_tx_descriptor *sun6i_dma_prep_slave_sg(
 	return vchan_tx_prep(&vchan->vc, &txd->vd, flags);
 
 err_lli_free:
-	for (p_lli = txd->p_lli, v_lli = txd->v_lli; v_lli;
-	     p_lli = v_lli->p_lli_next, v_lli = v_lli->v_lli_next)
-		dma_pool_free(sdev->pool, v_lli, p_lli);
+	sun6i_dma_free_lli_list(sdev, txd);
 	kfree(txd);
 	return NULL;
 }
@@ -869,9 +873,7 @@ static struct dma_async_tx_descriptor *sun6i_dma_prep_dma_cyclic(
 	return vchan_tx_prep(&vchan->vc, &txd->vd, flags);
 
 err_lli_free:
-	for (p_lli = txd->p_lli, v_lli = txd->v_lli; v_lli;
-	     p_lli = v_lli->p_lli_next, v_lli = v_lli->v_lli_next)
-		dma_pool_free(sdev->pool, v_lli, p_lli);
+	sun6i_dma_free_lli_list(sdev, txd);
 	kfree(txd);
 	return NULL;
 }
-- 
2.25.1