netdev - Re: [PATCH v2] net/ethtool/ioctl: ensure that we have phy ops before using them

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Date:   Wed, 23 Nov 2022 17:06:42 +0100
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     Daniil Tatianin <d-tatianin@...dex-team.ru>
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Michal Kubecek <mkubecek@...e.cz>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH v2] net/ethtool/ioctl: ensure that we have phy ops before using them

From: Daniil Tatianin <d-tatianin@...dex-team.ru>
Date: Tue, 22 Nov 2022 10:21:43 +0300

> ops->get_ethtool_phy_stats was getting called in an else branch
> of ethtool_get_phy_stats() unconditionally without making sure
> it was actually present.
> 
> Refactor the checks to avoid unnecessary nesting and make them more
> readable. Add an extra WARN_ON_ONCE(1) to emit a warning when a driver
> declares that it has phy stats without a way to retrieve them.
> 
> Found by Linux Verification Center (linuxtesting.org) with the SVACE
> static analysis tool.
> 
> Suggested-by: Jakub Kicinski <kuba@...nel.org>
> Signed-off-by: Daniil Tatianin <d-tatianin@...dex-team.ru>
> ---
>  net/ethtool/ioctl.c | 31 ++++++++++++++++++-------------
>  1 file changed, 18 insertions(+), 13 deletions(-)
> 
> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
> index 57e7238a4136..04f9ba98b038 100644
> --- a/net/ethtool/ioctl.c
> +++ b/net/ethtool/ioctl.c
> @@ -2100,23 +2100,28 @@ static int ethtool_get_phy_stats(struct net_device *dev, void __user *useraddr)
>  
>  	stats.n_stats = n_stats;
>  
> -	if (n_stats) {
> -		data = vzalloc(array_size(n_stats, sizeof(u64)));
> -		if (!data)
> -			return -ENOMEM;
> +	if (!n_stats) {
> +		data = NULL;
> +		goto copy_back;
> +	}
>  
> -		if (phydev && !ops->get_ethtool_phy_stats &&
> -		    phy_ops && phy_ops->get_stats) {
> -			ret = phy_ops->get_stats(phydev, &stats, data);
> -			if (ret < 0)
> -				goto out;
> -		} else {
> -			ops->get_ethtool_phy_stats(dev, &stats, data);
> -		}
> +	data = vzalloc(array_size(n_stats, sizeof(u64)));
> +	if (!data)
> +		return -ENOMEM;
> +
> +	if (ops->get_ethtool_phy_stats) {
> +		ops->get_ethtool_phy_stats(dev, &stats, data);

I'd first check for the callback and only after allocate the array,
otherwise there's no optimization in here.
Also, I'd separate saving 1 level of indent from the functional
changes.

> +	} else if (phydev && phy_ops && phy_ops->get_stats) {
> +		ret = phy_ops->get_stats(phydev, &stats, data);
> +		if (ret < 0)
> +			goto out;
>  	} else {
> -		data = NULL;
> +		WARN_ON_ONCE(1);
> +		n_stats = 0;
> +		stats.n_stats = 0;
>  	}
>  
> +copy_back:
>  	ret = -EFAULT;
>  	if (copy_to_user(useraddr, &stats, sizeof(stats)))
>  		goto out;
> -- 
> 2.25.1

Thanks,
Olek