netdev - Re: [PATCH] drivers/net/wan/hdlc_fr: Fix a double free in pvc

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Message-Id: <20210503060622.27128-1-xie.he.0141@gmail.com>
Date:   Sun,  2 May 2021 23:06:22 -0700
From:   Xie He <xie.he.0141@...il.com>
To:     Lv Yunlong <lyl2019@...l.ustc.edu.cn>
Cc:     khc@...waw.pl, davem@...emloft.net, kuba@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/net/wan/hdlc_fr: Fix a double free in pvc_xmit

> In pvc_xmit, if __skb_pad(skb, pad, false) failed, it will free
> the skb in the first time and goto drop. But the same skb is freed
> by kfree_skb(skb) in the second time in drop.
> 
> Maintaining the original function unchanged, my patch adds a new
> label out to avoid the double free if __skb_pad() failed.
> 
> Fixes: f5083d0cee08a ("drivers/net/wan/hdlc_fr: Improvements to the code of pvc_xmit")
> Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>
> ---
>  drivers/net/wan/hdlc_fr.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c
> index 0720f5f92caa..4d9dc7d15908 100644
> --- a/drivers/net/wan/hdlc_fr.c
> +++ b/drivers/net/wan/hdlc_fr.c
> @@ -415,7 +415,7 @@ static netdev_tx_t pvc_xmit(struct sk_buff *skb, struct net_device *dev)
>  
>  		if (pad > 0) { /* Pad the frame with zeros */
>  			if (__skb_pad(skb, pad, false))
> -				goto drop;
> +				goto out;
>  			skb_put(skb, pad);
>  		}
>  	}
> @@ -448,8 +448,9 @@ static netdev_tx_t pvc_xmit(struct sk_buff *skb, struct net_device *dev)
>  	return NETDEV_TX_OK;
>  
>  drop:
> -	dev->stats.tx_dropped++;
>  	kfree_skb(skb);
> +out:
> +	dev->stats.tx_dropped++;
>  	return NETDEV_TX_OK;
>  }
> 

1. This patch is incorrect. "__skb_pad" will NOT free the skb on failure
when its "free_on_error" parameter is "false".

2. If you think you fix my commit, please CC me so that I can review
your patch.

I have sent another patch to revert this.