netdev - Re: [PATCH 4/4] net: hns3: double free 'skb'

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Date:   Wed, 3 Feb 2021 11:51:10 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Wenjia Zhao <driverfuzzing@...il.com>
CC:     Yisen Zhuang <yisen.zhuang@...wei.com>,
        Salil Mehta <salil.mehta@...wei.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Jakub Kicinski" <kuba@...nel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] net: hns3: double free 'skb'

On 2021/2/3 11:13, Wenjia Zhao wrote:
> net: hns3: double free 'skb'
> 
> The false branch of (tx_ret == NETDEV_TX_OK) free the skb. However, the
> kfree_skb(skb) in the out label will be execute when exits the function.
> So the skb has a double-free bugs.
> 
> Remove the kfree_skb(skb) at line 269

The freeing is added by the below patch:

commit: 8f9eed1a8791("net: hns3: fix for skb leak when doing selftest")

which is to fix a skb leak problem.

kfree_skb(skb) in the out label corresponds to alloc_skb(),
and kfree_skb(skb) removed in this patch corresponds to
skb_get(skb) before calling hns3_nic_net_xmit() when
hns3_nic_net_xmit() non-NETDEV_TX_OK.

So I do not think there is double free 'skb' here, unless
I miss something here?

> 
> Signed-off-by: Wenjia Zhao <driverfuzzing@...il.com>
> ---
>  drivers/net/ethernet/hisilicon/hns3/hns3_ethtool.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3_ethtool.c b/drivers/net/ethernet/hisilicon/hns3/hns3_ethtool.c
> index 2622e04..1b926ff 100644
> --- a/drivers/net/ethernet/hisilicon/hns3/hns3_ethtool.c
> +++ b/drivers/net/ethernet/hisilicon/hns3/hns3_ethtool.c
> @@ -266,7 +266,6 @@ static int hns3_lp_run_test(struct net_device *ndev, enum hnae3_loop mode)
>  		if (tx_ret == NETDEV_TX_OK) {
>  			good_cnt++;
>  		} else {
> -			kfree_skb(skb);
>  			netdev_err(ndev, "hns3_lb_run_test xmit failed: %d\n",
>  				   tx_ret);
>  		}
>