netdev - Re: [PATCH] net: ethtool: not call vzalloc for zero sized memory request

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Date:   Thu, 28 Mar 2019 10:09:02 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Li RongQing <lirongqing@...du.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH] net: ethtool: not call vzalloc for zero sized memory
 request

On Thu, Mar 28, 2019 at 02:01:09PM +0800, Li RongQing wrote:
> NULL or ZERO_SIZE_PTR will be returned for zero sized memory
> request, and derefencing them will lead to a segfault
> 
> so it is unnecessory to call vzalloc for zero sized memory
> request and not call __ethtool_get_strings which always uses
> the allocated memory
> 
> this also fixes a possible memory leak if phy_ethtool_get_stats
> returns error, memory should be freed before exit
> 
> Signed-off-by: Li RongQing <lirongqing@...du.com>
> Reviewed-by: Wang Li <wangli39@...du.com>
> ---
>  net/core/ethtool.c | 37 ++++++++++++++++++++++++++-----------
>  1 file changed, 26 insertions(+), 11 deletions(-)
> 
> diff --git a/net/core/ethtool.c b/net/core/ethtool.c
> index b1eb32419732..3e971a36e37c 100644
> --- a/net/core/ethtool.c
> +++ b/net/core/ethtool.c
...
> @@ -1897,9 +1902,14 @@ static int ethtool_get_stats(struct net_device *dev, void __user *useraddr)
>  		return -EFAULT;
>  
>  	stats.n_stats = n_stats;
> -	data = vzalloc(array_size(n_stats, sizeof(u64)));
> -	if (n_stats && !data)
> -		return -ENOMEM;
> +
> +	if (n_stats) {
> +		data = vzalloc(array_size(n_stats, sizeof(u64)));
> +		if (!data)
> +			return -ENOMEM;
> +	} else {
> +		data = NULL;
> +	}
>  
>  	ops->get_ethtool_stats(dev, &stats, data);
>  

You avoid the vzalloc() call here but you still pass null data pointer
to device's get_ethtool_stats() handler which seems to contradict what
the commit message says. Is it really what you want? (The same applies
to ethtool_get_phy_stats() below.)

Michal

> @@ -1941,14 +1951,19 @@ static int ethtool_get_phy_stats(struct net_device *dev, void __user *useraddr)
>  		return -EFAULT;
>  
>  	stats.n_stats = n_stats;
> -	data = vzalloc(array_size(n_stats, sizeof(u64)));
> -	if (n_stats && !data)
> -		return -ENOMEM;
> +
> +	if (n_stats) {
> +		data = vzalloc(array_size(n_stats, sizeof(u64)));
> +		if (!data)
> +			return -ENOMEM;
> +	} else {
> +		data = NULL;
> +	}
>  
>  	if (dev->phydev && !ops->get_ethtool_phy_stats) {
>  		ret = phy_ethtool_get_stats(dev->phydev, &stats, data);
>  		if (ret < 0)
> -			return ret;
> +			goto out;
>  	} else {
>  		ops->get_ethtool_phy_stats(dev, &stats, data);
>  	}
> -- 
> 2.16.2
>