Re: [PATCH v2 2/2] dmaengine: loongson1: guard issue_pending against empty lli_list

[Frank Li]

On Tue, Nov 03, 2026 at 04:46:38PM +0800, Li Ximo wrote:
> From: Wang Haoran <haoranwangsec@xxxxxxxxx>
>
> ls1x_dma_issue_pending() calls list_first_entry(&desc->lli_list, ...)

list_first_entry()

> without checking whether the list is empty. list_first_entry() does not
> return NULL for an empty list; it returns the container_of() of the list
> head pointer, i.e. a wild pointer into the enclosing
> struct ls1x_dma_desc/virt_dma_desc area.

> The bogus &lli->phys is then
> passed to ls1x_dma_start(), which dereferences it (out-of-bounds read)
> and programs the DMA controller with the garbage address.
>

Cut this paragraph

> Switch to list_first_entry_or_null() with a NULL check so an empty
> lli_list can never reach the hardware programming path.

> The companion
> patch rejects the known producer of such descriptors (sg_len == 0 in
> ls1x_dma_prep_slave_sg()); this guard covers any remaining path.

Cut this paragraph.

This common issue about list_first_entry(). Keep commit message simple
and leave important informaiton.

Frank

>
> This issue was found by static analysis.
>
> Reported-by: Wang Haoran <haoranwangsec@xxxxxxxxx>
> Reported-by: Li Ximo <lixicaicai@xxxxxxxxx>
> Signed-off-by: Wang Haoran <haoranwangsec@xxxxxxxxx>
> ---
> v1: https://lore.kernel.org/r/20261026115113.3359939-1-lixicaicai@xxxxxxxxx
> v2: split the two independent fixes into separate patches as requested
> by Frank Li; no code change.
>
>  drivers/dma/loongson/loongson1-apb-dma.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma/loongson/loongson1-apb-dma.c b/drivers/dma/loongson/loongson1-apb-dma.c
> index 89786cbd2..e7eb40584 100644
> --- a/drivers/dma/loongson/loongson1-apb-dma.c
> +++ b/drivers/dma/loongson/loongson1-apb-dma.c
> @@ -478,8 +481,11 @@ static void ls1x_dma_issue_pending(struct dma_chan *dchan)
>  			struct ls1x_dma_desc *desc = to_ls1x_dma_desc(vd);
>  			struct ls1x_dma_lli *lli;
>
> -			lli = list_first_entry(&desc->lli_list,
> -					       struct ls1x_dma_lli, node);
> +			lli = list_first_entry_or_null(&desc->lli_list,
> +						       struct ls1x_dma_lli, node);
> +			if (!lli)
> +				return;
> +
>  			ls1x_dma_start(chan, &lli->phys);
>  		}
>  	}
> --
> 2.30.2