Subject: Re: [PATCH net] net: phy: fix potential use of NULL pointer in phy_suspend()

From: "Russell King (Oracle)" <[email-masked]>
Date: Fri, 28 Jun 2024 11:33:26 +0100

On Fri, Jun 28, 2024 at 11:32:11AM +0100, Russell King (Oracle) wrote:
> phy_suspend() checks the WoL status, and then dereferences
> phydrv->flags if (and only if) we decided that WoL has been enabled
> on either the PHY or the netdev.
> 
> We then check whether phydrv was NULL, but we've potentially already
> dereferenced the pointer.
> 
> If phydrv is NULL, then phy_ethtool_get_wol() will return an error
> and leave wol.wolopts set to zero. However, if netdev->wol_enabled
> is true, then we would dereference a NULL pointer.
> 
> Checking the PHY drivers, the only place that phydev->wol_enabled is
> checked by them is in their suspend/resume callbacks and nowhere else
> (which is correct, because phylib only updates this in phy_suspend()).
> 
> So, move the NULL pointer check earlier to avoid a NULL pointer
> dereference. Leave the check for phydrv->suspend in place as a driver
> may populate the .resume method but not the .suspend method.
> 
> Signed-off-by: Russell King (Oracle) <[email-masked]>
> ---

Note - I don't believe anyone has hit this condition, so maybe we want
the patch for net-next rather than net? For now I have the patch
against both trees so let me know which you'd prefer.

>  drivers/net/phy/phy_device.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 6c6ec9475709..19f8ae113dd3 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -1980,7 +1980,7 @@ int phy_suspend(struct phy_device *phydev)
>  	const struct phy_driver *phydrv = phydev->drv;
>  	int ret;
>  
> -	if (phydev->suspended)
> +	if (phydev->suspended || !phydrv)
>  		return 0;
>  
>  	phy_ethtool_get_wol(phydev, &wol);
> @@ -1989,7 +1989,7 @@ int phy_suspend(struct phy_device *phydev)
>  	if (phydev->wol_enabled && !(phydrv->flags & PHY_ALWAYS_CALL_SUSPEND))
>  		return -EBUSY;
>  
> -	if (!phydrv || !phydrv->suspend)
> +	if (!phydrv->suspend)
>  		return 0;
>  
>  	ret = phydrv->suspend(phydev);
> -- 
> 2.30.2
> 
> 

-- 
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