Re: [PATCH net-next] net: phylink: reject unsupported speed/duplex in ksettings_set() with PHY

[Andrew Lunn]

On Mon, Jul 06, 2026 at 11:27:35PM -0700, muhammad.nazim.amirul.nazle.asmade@xxxxxxxxxx wrote:
> From: Nazim Amirul <muhammad.nazim.amirul.nazle.asmade@xxxxxxxxxx>
> 
> When using ethtool to change speed and duplex on a phylink-managed
> interface with a PHY attached, the requested speed/duplex combination
> is not validated against the MAC's supported capabilities before being
> passed down to the PHY layer.

How are you invoking ethtool here? And what other invocations have you
tested, with this patch in place?

> @@ -2989,6 +2989,10 @@ int phylink_ethtool_ksettings_set(struct phylink *pl,
>  	if (pl->phydev) {
>  		struct ethtool_link_ksettings phy_kset = *kset;
>  
> +		if (!phy_caps_lookup(kset->base.speed, kset->base.duplex,
> +				     pl->supported, true))
> +			return -EINVAL;

Are base.speed and base.duplex always set? When looking at
phy_ethtool_ksettings_set() the values are only used when base.autoneg
is false. So maybe they are not always valid?

   Andrew