[PATCH] 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>
---
 drivers/dma/sun6i-dma.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
index a9a254dbf8cb..eb9c4ae87ac8 100644
--- a/drivers/dma/sun6i-dma.c
+++ b/drivers/dma/sun6i-dma.c
@@ -788,9 +788,15 @@ 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)
+	p_lli = txd->p_lli;
+	v_lli = txd->v_lli;
+	while (v_lli) {
+		struct sun6i_dma_lli *next_v_lli = v_lli->v_lli_next;
+		dma_addr_t next_p_lli = v_lli->p_lli_next;
 		dma_pool_free(sdev->pool, v_lli, p_lli);
+		v_lli = next_v_lli;
+		p_lli = next_p_lli;
+	}
 	kfree(txd);
 	return NULL;
 }
@@ -869,9 +875,15 @@ 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)
+	p_lli = txd->p_lli;
+	v_lli = txd->v_lli;
+	while (v_lli) {
+		struct sun6i_dma_lli *next_v_lli = v_lli->v_lli_next;
+		dma_addr_t next_p_lli = v_lli->p_lli_next;
 		dma_pool_free(sdev->pool, v_lli, p_lli);
+		v_lli = next_v_lli;
+		p_lli = next_p_lli;
+	}
 	kfree(txd);
 	return NULL;
 }
-- 
2.25.1