linux-kernel - Re: [PATCH v2] hv_netvsc: fix a possible NULL pointer dereference in netvsc_get_ethtool

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Message-Id: <20190313.140837.1079383755054713181.davem@davemloft.net>
Date:   Wed, 13 Mar 2019 14:08:37 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     kjlu@....edu
Cc:     pakki001@....edu, kys@...rosoft.com, haiyangz@...rosoft.com,
        sthemmin@...rosoft.com, sashal@...nel.org,
        linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] hv_netvsc: fix a possible NULL pointer dereference
 in netvsc_get_ethtool_stats()

From: Kangjie Lu <kjlu@....edu>
Date: Tue, 12 Mar 2019 00:01:49 -0500

> In case kvmalloc_array fails, we should stop using it to avoid
> NULL pointer dereference.
> 
> Signed-off-by: Kangjie Lu <kjlu@....edu>
> ---
>  drivers/net/hyperv/netvsc_drv.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
> index cf4897043e83..4b3a03029fe8 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -1426,6 +1426,9 @@ 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)
> +		return;
> +
>  	netvsc_get_pcpu_stats(dev, pcpu_sum);
>  	for_each_present_cpu(cpu) {
>  		struct netvsc_ethtool_pcpu_stats *this_sum = &pcpu_sum[cpu];

What a surprise it will be when the user's statistics monitoring
software sees values suddenly drop to zero with no error indication
whatsoever.