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

["Jernej Škrabec" <jernej.skrabec@gmail.com>]

Dne četrtek, 11. junij 2026 ob 08:36:31 Srednjeevropski poletni čas je Hongling Zeng napisal(a):
> 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>
> ---
>  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;
>  }
> 

This is certainly a valid fix, but it's replicating what sun6i_dma_free_desc()
is already doing. It would be better to split code to accept struct sun6i_desc
*txd parameter and call that instead from all places.

Best regards,
Jernej