netdev - Re: [PATCH] hv_netvsc: Add check for kvmalloc

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Date:   Fri, 11 Mar 2022 09:25:38 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, davem@...emloft.net,
        kuba@...nel.org, ast@...nel.org, daniel@...earbox.net,
        hawk@...nel.org, john.fastabend@...il.com, andrii@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com,
        kpsingh@...nel.org, linux-hyperv@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH] hv_netvsc: Add check for kvmalloc_array

On Fri, 11 Mar 2022 11:20:35 +0800
Jiasheng Jiang <jiasheng@...as.ac.cn> wrote:

> As the potential failure of the kvmalloc_array(),
> it should be better to check and restore the 'data'
> if fails in order to avoid the dereference of the
> NULL pointer.
> 
> Fixes: 6ae746711263 ("hv_netvsc: Add per-cpu ethtool stats for netvsc")
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
>  drivers/net/hyperv/netvsc_drv.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
> index 3646469433b1..018c4a5f6f44 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -1587,6 +1587,12 @@ static void netvsc_get_ethtool_stats(struct net_device *dev,
>  	pcpu_sum = kvmalloc_array(num_possible_cpus(),
>  				  sizeof(struct netvsc_ethtool_pcpu_stats),
>  				  GFP_KERNEL);
> +	if (!pcpu_sum) {
> +		for (j = 0; j < i; j++)
> +			data[j] = 0;
> +		return;
> +	}

I don't think you understood what my comment was.

The zeroing here is not necessary. Just do:
        if (!pcpu_sum)
               return;

The data pointer is to buffer allocated here:

static int ethtool_get_stats(struct net_device *dev, void __user *useraddr)
{
...
	if (n_stats) {
		data = vzalloc(array_size(n_stats, sizeof(u64)));  <<<<< is already zeroed.
		if (!data)
			return -ENOMEM;
		ops->get_ethtool_stats(dev, &stats, data);