Re: [PATCH v4] dmaengine: sun6i-dma: Fix use-after-free in error handling paths

[Frank Li <Frank.li@oss.nxp.com>]

On Wed, Jul 08, 2026 at 11:25:18AM +0800, Hongling Zeng wrote:
> 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.
>

Is this statement out of date? You call sun6i_dma_free_desc_virt()
where saving "both the next virtual and physical pointers..."?

Frank

> 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>
> Reviewed-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
> ---
> Change in v4:
>  -Add reviewed-by
> ---
>  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 fcc88a74d821..e161fc298b86 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;
>  }
>
> @@ -1432,7 +1433,7 @@ 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
>