[PATCH v3] dmaengine: sun6i-dma: Fix use-after-free in error handling paths

[PATCH v3] 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@kylinos.cn>
Suggested-by: Jernej Skrabec <jernej.skrabec@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@gmail.com>

---
Change in v3:
 -Further refactoring to move txd handling into the helper function
  as suggested by Jernej
---
 drivers/dma/sun6i-dma.c | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
index a9a254dbf8cb..7a79f346250a 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_desc(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;
 
@@ -432,6 +428,17 @@ static void sun6i_dma_free_desc(struct virt_dma_desc *vd)
 	kfree(txd);
 }
 
+static void sun6i_dma_free_desc_virt(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_desc(sdev, txd);
+}
+
 static int sun6i_dma_start_desc(struct sun6i_vchan *vchan)
 {
 	struct sun6i_dma_dev *sdev = to_sun6i_dma_dev(vchan->vc.chan.device);
@@ -788,10 +795,7 @@ 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);
-	kfree(txd);
+	sun6i_dma_free_desc(sdev, txd);
 	return NULL;
 }
 
@@ -869,10 +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);
-	kfree(txd);
+	sun6i_dma_free_desc(sdev, txd);
 	return NULL;
 }
 
@@ -1431,7 +1432,7 @@ static int sun6i_dma_probe(struct platform_device *pdev)
 		struct sun6i_vchan *vchan = &sdc->vchans[i];
 
 		INIT_LIST_HEAD(&vchan->node);
-		vchan->vc.desc_free = sun6i_dma_free_desc;
+		vchan->vc.desc_free = sun6i_dma_free_desc_virt;
 		vchan_init(&vchan->vc, &sdc->slave);
 	}
 
-- 
2.25.1

Re: [PATCH v3] dmaengine: sun6i-dma: Fix use-after-free in error handling paths

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Memory leak in `sun6i_dma_terminate_all` for active non-cyclic descriptors.
--

commit 81994b3beae8e2aae413048bdddddd1fbb74bec0
Author: Hongling Zeng <zenghongling@kylinos.cn>

dmaengine: sun6i-dma: Fix use-after-free in error handling paths
    
This patch fixes a use-after-free during the error handling path of
sun6i_dma_prep_slave_sg and sun6i_dma_prep_dma_cyclic. It replaces an
unsafe manual loop traversal with a call to sun6i_dma_free_desc(),
which safely stores the next pointers before freeing the current LLI.

> diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> index a9a254dbf8cb9..7a79f346250a5 100644
> --- a/drivers/dma/sun6i-dma.c
> +++ b/drivers/dma/sun6i-dma.c

[ ... ]

While looking at this driver's descriptor cleanup, I noticed a separate
issue in sun6i_dma_terminate_all():

drivers/dma/sun6i-dma.c:sun6i_dma_terminate_all()
	if (vchan->cyclic) {
		vchan->cyclic = false;
		if (pchan && pchan->desc) {
			struct virt_dma_desc *vd = &pchan->desc->vd;
			struct virt_dma_chan *vc = &vchan->vc;

			list_add_tail(&vd->node, &vc->desc_completed);
		}
	}

	vchan_get_all_descriptors(&vchan->vc, &head);

	if (pchan) {
		writel(DMA_CHAN_ENABLE_STOP, pchan->base + DMA_CHAN_ENABLE);
		writel(DMA_CHAN_PAUSE_RESUME, pchan->base + DMA_CHAN_PAUSE);

		vchan->phy = NULL;
		pchan->vchan = NULL;
		pchan->desc = NULL;
                ^^^^^^^^^^^^^^^^^^
[Severity: High]
This is a pre-existing issue, but does this leak the active non-cyclic
descriptor?

When a non-cyclic transfer is aborted, pchan->desc is not added to the
desc_completed list (unlike cyclic transfers). Because it was already
removed from the desc_issued list during sun6i_dma_start_desc(),
setting pchan->desc to NULL here seems to permanently orphan the
descriptor and its associated LLIs, leading to a memory leak.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260616023138.15904-1-zenghongling@kylinos.cn?part=1