netdev - Re: [PATCH] i40e: Fix potential invalid access when MAC list is empty

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Message-ID: <a9a2de1b-6432-447e-a446-741c5a8e53b4@intel.com>
Date: Wed, 27 Aug 2025 09:47:12 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Zhen Ni <zhen.ni@...ystack.cn>
CC: <intel-wired-lan@...ts.osuosl.org>, <netdev@...r.kernel.org>,
	<anthony.l.nguyen@...el.com>, <andrew+netdev@...n.ch>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH] i40e: Fix potential invalid access when MAC list is empty

On 8/27/25 05:23, Zhen Ni wrote:
> list_first_entry() never returns NULL — if the list is empty, it still
> returns a pointer to an invalid object, leading to potential invalid
> memory access when dereferenced.
> 
> Fix this by checking list_empty() before calling list_first_entry(),
> and only copying the MAC address when the list is not empty.

good observation, thank you for reaching out!
what about using list_first_entry_or_null() instead of splitting into
two operations?

next time please tag intel ethernet patches as PATCH iwl-net (for fixes,
like here) or PATCH iwl-next (for features/refactors)

> 
> Fixes: e3219ce6a775 ("i40e: Add support for client interface for IWARP driver")
> Signed-off-by: Zhen Ni <zhen.ni@...ystack.cn>
> ---
>   drivers/net/ethernet/intel/i40e/i40e_client.c | 9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_client.c b/drivers/net/ethernet/intel/i40e/i40e_client.c
> index 5f1a405cbbf8..0a72157aee0e 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_client.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_client.c
> @@ -359,12 +359,13 @@ static void i40e_client_add_instance(struct i40e_pf *pf)
>   	if (i40e_client_get_params(vsi, &cdev->lan_info.params))
>   		goto free_cdev;
>   
> -	mac = list_first_entry(&cdev->lan_info.netdev->dev_addrs.list,
> -			       struct netdev_hw_addr, list);
> -	if (mac)
> +	if (!list_empty(&cdev->lan_info.netdev->dev_addrs.list)) {
> +		mac = list_first_entry(&cdev->lan_info.netdev->dev_addrs.list,
> +				       struct netdev_hw_addr, list);
>   		ether_addr_copy(cdev->lan_info.lanmac, mac->addr);
> -	else
> +	} else {
>   		dev_err(&pf->pdev->dev, "MAC address list is empty!\n");
> +	}
>   
>   	pf->cinst = cdev;
>