netdev - Re: [PATCH net-next] net: dm9051: Fix use after free in dm9051_loop

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Date:   Fri, 18 Feb 2022 21:07:12 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Joseph CHAMG <josright123@...il.com>, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net-next] net: dm9051: Fix use after free in
 dm9051_loop_tx()

On Fri, 18 Feb 2022 18:27:30 +0300 Dan Carpenter wrote:
> This code dereferences "skb" after calling dev_kfree_skb().
> 
> Fixes: 2dc95a4d30ed ("net: Add dm9051 driver")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

Thanks!  Although..

> diff --git a/drivers/net/ethernet/davicom/dm9051.c b/drivers/net/ethernet/davicom/dm9051.c
> index a63d17e669a0..f6b5d2becf5e 100644
> --- a/drivers/net/ethernet/davicom/dm9051.c
> +++ b/drivers/net/ethernet/davicom/dm9051.c
> @@ -850,13 +850,13 @@ static int dm9051_loop_tx(struct board_info *db)
>  		if (skb) {
>  			ntx++;
>  			ret = dm9051_single_tx(db, skb->data, skb->len);
> +			ndev->stats.tx_bytes += skb->len;
> +			ndev->stats.tx_packets++;
>  			dev_kfree_skb(skb);
>  			if (ret < 0) {
>  				db->bc.tx_err_counter++;
>  				return 0;
>  			}
> -			ndev->stats.tx_bytes += skb->len;
> -			ndev->stats.tx_packets++;

I think the idea was (and it often is with this kind of bugs)
to count only successful transmissions. Could you re-jig it 
a little to keep those semantics?