Re: [PATCH] dmaengine: at_xdmac: fix potential Oops in at_xdmac_prep_interleaved()

[Tudor Ambarus <tudor.ambarus@linaro.org>]

On 5/15/23 11:32, Dan Carpenter wrote:
> There are two place if the at_xdmac_interleaved_queue_desc() fails which
> could lead to a NULL dereference where "first" is NULL and we call
> list_add_tail(&first->desc_node, ...).  In the first caller, the return
> is not checked so add a check for that.  In the next caller, the return
> is checked but if it fails on the first iteration through the loop then
> it will lead to a NULL pointer dereference.
> 
> Fixes: 4e5385784e69 ("dmaengine: at_xdmac: handle numf > 1")
> Fixes: 62b5cb757f1d ("dmaengine: at_xdmac: fix memory leak in interleaved mode")
> Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>

Reviewed-by: Tudor Ambarus <tudor.ambarus@linaro.org>

> ---
>  drivers/dma/at_xdmac.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> index 7da6d9b6098e..c3b37168b21f 100644
> --- a/drivers/dma/at_xdmac.c
> +++ b/drivers/dma/at_xdmac.c
> @@ -1102,6 +1102,8 @@ at_xdmac_prep_interleaved(struct dma_chan *chan,
>  							NULL,
>  							src_addr, dst_addr,
>  							xt, xt->sgl);
> +		if (!first)
> +			return NULL;
>  
>  		/* Length of the block is (BLEN+1) microblocks. */
>  		for (i = 0; i < xt->numf - 1; i++)
> @@ -1132,8 +1134,9 @@ at_xdmac_prep_interleaved(struct dma_chan *chan,
>  							       src_addr, dst_addr,
>  							       xt, chunk);
>  			if (!desc) {
> -				list_splice_tail_init(&first->descs_list,
> -						      &atchan->free_descs_list);
> +				if (first)
> +					list_splice_tail_init(&first->descs_list,
> +							      &atchan->free_descs_list);
>  				return NULL;
>  			}
>