Re: [PATCH v2 2/2] dmaengine: sun6i: fix undefined behaviour in sun6i_dma_tx_status

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

On Fri, Aug 14, 2026 at 04:21:11PM +0200, Christian Lugnberg wrote:
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>
> sun6i_dma_tx_status() calls vchan_find_desc() to look up the virtual
> descriptor for a given cookie, before checking whether the pointer
> vd is NULL:
>
>     vd = vchan_find_desc(&vchan->vc, cookie);
>     txd = to_sun6i_desc(&vd->tx);   /* vd may be NULL here */
>
>     if (vd) {
>         for (lli = txd->v_lli; ...)
>
> vchan_find_desc() returns NULL when the descriptor has already been
> completed or is in-flight on a physical channel and no longer present
> in the virtual channel's descriptor list. When vd is NULL,
> to_sun6i_desc() is called unconditionally on &vd->tx before the NULL
> check, which is undefined behaviour. Move the call inside the if (vd)
> guard to ensure it is only reached with a valid pointer.
>
>     vd = vchan_find_desc(&vchan->vc, cookie);
>     if (vd) {
>         struct sun6i_desc *txd = to_sun6i_desc(&vd->tx);
>         for (lli = txd->v_lli; ...)
>
> Fixes: 555859308723 ("dmaengine: sun6i: Add driver for the Allwinner A31 DMA controller")
> Cc: stable@vger.kernel.org
> Assisted-by: Claude:claude-sonnet-4-6
> Signed-off-by: Christian Lugnberg <christian.lugnberg@soundtrack.io>
> ---

Reviewed-by: Frank Li <Frank.Li@nxp.com>

>  drivers/dma/sun6i-dma.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> index 04fe1f5042e9..7704b016aed8 100644
> --- a/drivers/dma/sun6i-dma.c
> +++ b/drivers/dma/sun6i-dma.c
> @@ -981,7 +981,6 @@ static enum dma_status sun6i_dma_tx_status(struct dma_chan *chan,
>         struct sun6i_pchan *pchan = vchan->phy;
>         struct sun6i_dma_lli *lli;
>         struct virt_dma_desc *vd;
> -       struct sun6i_desc *txd;
>         enum dma_status ret;
>         unsigned long flags;
>         size_t bytes = 0;
> @@ -993,9 +992,9 @@ static enum dma_status sun6i_dma_tx_status(struct dma_chan *chan,
>         spin_lock_irqsave(&vchan->vc.lock, flags);
>
>         vd = vchan_find_desc(&vchan->vc, cookie);
> -       txd = to_sun6i_desc(&vd->tx);
>
>         if (vd) {
> +               struct sun6i_desc *txd = to_sun6i_desc(&vd->tx);
>                 for (lli = txd->v_lli; lli != NULL; lli = lli->v_lli_next)
>                         bytes += lli->len;
>         } else if (!pchan || !pchan->desc) {
> --
> 2.54.0 (Apple Git-156)
>