Re: [PATCH] net: mediatek: add null pointer check for hardware offloading

[Vadim Fedorenko <vadim.fedorenko@linux.dev>]

On 31/12/2025 22:52, Sebastian Roland Wolf wrote:
> From: Sebastian Roland Wolf <srw@root533.premium-rootserver.net>
> 
> Add a null pointer check to prevent kernel crashes when hardware
> offloading is active on MediaTek devices.
> 
> In some edge cases, the ethernet pointer or its associated netdev
> element can be NULL. Checking these pointers before access is
> mandatory to avoid segmentation faults and kernel oops.
> 
> This improves the robustness of the validation check for mtk_eth
> ingress devices introduced in commit 73cfd947dbdb ("net: mediatek:
> add support for ingress traffic offloading").
> 
> Fixes: 73cfd947dbdb ("net: mediatek: add support for ingress traffic offloading")
> net: mediatek: Add null pointer check to prevent crashes with active hardware offloading.
> 
> Signed-off-by: Sebastian Roland Wolf <Sebastian.Wolf@pace-systems.de>
> ---
>   drivers/net/ethernet/mediatek/mtk_ppe_offload.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_ppe_offload.c b/drivers/net/ethernet/mediatek/mtk_ppe_offload.c
> index e9bd32741983..6900ac87e1e9 100644
> --- a/drivers/net/ethernet/mediatek/mtk_ppe_offload.c
> +++ b/drivers/net/ethernet/mediatek/mtk_ppe_offload.c
> @@ -270,7 +270,8 @@ mtk_flow_offload_replace(struct mtk_eth *eth, struct flow_cls_offload *f,
>   		flow_rule_match_meta(rule, &match);
>   		if (mtk_is_netsys_v2_or_greater(eth)) {

The code dereferences eth here ...

>   			idev = __dev_get_by_index(&init_net, match.key->ingress_ifindex);
> -			if (idev && idev->netdev_ops == eth->netdev[0]->netdev_ops) {
> +			if (idev && eth && eth->netdev[0] &&

... but it is checked a couple of lines after.

Even more, the function starts with providing rhahstable to lookup
cookie. I'm really doubt eth can be NULL.
At the same time lack of eth->netdev[0] looks like a design problem,
because according to the code there might be up to 3 netdev devices
registered for ppe.

I'm not familiar with the code, but it would be better to have a splat
of crash to check what was exactly missing, and drgn can help you find
if there were other netdevs available at the moment of crash.

> +			    idev->netdev_ops == eth->netdev[0]->netdev_ops) {
>   				struct mtk_mac *mac = netdev_priv(idev);
>   
>   				if (WARN_ON(mac->ppe_idx >= eth->soc->ppe_num))