netdev - Re: [PATCH net] net: ftgmac100: fix potential NULL pointer access in ftgmac100_phy

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Message-ID: <ddbfdf8c-53ab-4993-a53a-60c45d36cae9@linux.intel.com>
Date: Thu, 31 Jul 2025 10:58:47 +0200
From: Dawid Osuchowski <dawid.osuchowski@...ux.intel.com>
To: Heiner Kallweit <hkallweit1@...il.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, Simon Horman <horms@...nel.org>,
 Jakub Kicinski <kuba@...nel.org>, David Miller <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>
Cc: Jacky Chou <jacky_chou@...eedtech.com>,
 Jacob Keller <jacob.e.keller@...el.com>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net: ftgmac100: fix potential NULL pointer access in
 ftgmac100_phy_disconnect

On 2025-07-30 10:23 PM, Heiner Kallweit wrote:
> After the call to phy_disconnect() netdev->phydev is reset to NULL.

phy_disconnect() in its flow does not set phydev to NULL, if anywhere it 
happens in of_phy_deregister_fixed_link(), which already calls 
fixed_phy_unregister() before setting phydev to NULL

 From my understanding (which very much could be wrong) of 
ftgmac100_probe(), these two cases are mutually exclusive. The device 
either uses NCSI or will use a phy based on the DT "fixed-link" property
> So fixed_phy_unregister() would be called with a NULL pointer as argument.

Given my analysis above, I don't think this case is possible.

Best regards,
Dawid
> Therefore cache the phy_device before this call.
> 
> Fixes: e24a6c874601 ("net: ftgmac100: Get link speed and duplex for NC-SI")
> Cc: stable@...r.kernel.org
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> ---
>   drivers/net/ethernet/faraday/ftgmac100.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/faraday/ftgmac100.c b/drivers/net/ethernet/faraday/ftgmac100.c
> index 5d0c09068..a863f7841 100644
> --- a/drivers/net/ethernet/faraday/ftgmac100.c
> +++ b/drivers/net/ethernet/faraday/ftgmac100.c
> @@ -1750,16 +1750,17 @@ static int ftgmac100_setup_mdio(struct net_device *netdev)
>   static void ftgmac100_phy_disconnect(struct net_device *netdev)
>   {
>   	struct ftgmac100 *priv = netdev_priv(netdev);
> +	struct phy_device *phydev = netdev->phydev;
>   
> -	if (!netdev->phydev)
> +	if (!phydev)
>   		return;
>   
> -	phy_disconnect(netdev->phydev);
> +	phy_disconnect(phydev);
>   	if (of_phy_is_fixed_link(priv->dev->of_node))
>   		of_phy_deregister_fixed_link(priv->dev->of_node);
>   
>   	if (priv->use_ncsi)
> -		fixed_phy_unregister(netdev->phydev);
> +		fixed_phy_unregister(phydev);
>   }
>   
>   static void ftgmac100_destroy_mdio(struct net_device *netdev)