linux-kernel - Re: Re: [PATCH] ethernet/realtek/r8169: Fix a double free in rtl8169_start

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Date:   Mon, 29 Mar 2021 18:11:05 +0800 (GMT+08:00)
From:   lyl2019@...l.ustc.edu.cn
To:     "Heiner Kallweit" <hkallweit1@...il.com>
Cc:     nic_swsd@...ltek.com, kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH] ethernet/realtek/r8169: Fix a double free in
 rtl8169_start_xmit




> -----原始邮件-----
> 发件人: "Heiner Kallweit" <hkallweit1@...il.com>
> 发送时间: 2021-03-29 17:51:30 (星期一)
> 收件人: "Lv Yunlong" <lyl2019@...l.ustc.edu.cn>, nic_swsd@...ltek.com, kuba@...nel.org
> 抄送: netdev@...r.kernel.org, linux-kernel@...r.kernel.org
> 主题: Re: [PATCH] ethernet/realtek/r8169: Fix a double free in rtl8169_start_xmit
> 
> On 29.03.2021 11:02, Lv Yunlong wrote:
> > In rtl8169_start_xmit, it calls rtl8169_tso_csum_v2(tp, skb, opts) and
> > rtl8169_tso_csum_v2() calls __skb_put_padto(skb, padto, false). If
> > __skb_put_padto() failed, it will free the skb in the first time and
> > return error. Then rtl8169_start_xmit will goto err_dma_0.
> > 
> 
> No, the skb isn't freed here in case of error. Have a look at the
> implementation of __skb_put_padto() and see also cc6528bc9a0c
> ("r8169: fix potential skb double free in an error path").
> 
> 
> > But in err_dma_0 label, the skb is freed by dev_kfree_skb_any(skb) in
> > the second time.
> > 
> > My patch adds a new label inside the old err_dma_0 label to avoid the
> > double free and renames the error labels to keep the origin function
> > unchanged.
> > 
> > Fixes: b8447abc4c8fb ("r8169: factor out rtl8169_tx_map")
> > Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>
> > ---
> >  drivers/net/ethernet/realtek/r8169_main.c | 9 +++++----
> >  1 file changed, 5 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
> > index f704da3f214c..91c43399712b 100644
> > --- a/drivers/net/ethernet/realtek/r8169_main.c
> > +++ b/drivers/net/ethernet/realtek/r8169_main.c
> > @@ -4217,13 +4217,13 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
> >  
> >  	if (unlikely(rtl8169_tx_map(tp, opts, skb_headlen(skb), skb->data,
> >  				    entry, false)))
> > -		goto err_dma_0;
> > +		goto err_dma_1;
> >  
> >  	txd_first = tp->TxDescArray + entry;
> >  
> >  	if (frags) {
> >  		if (rtl8169_xmit_frags(tp, skb, opts, entry))
> > -			goto err_dma_1;
> > +			goto err_dma_2;
> >  		entry = (entry + frags) % NUM_TX_DESC;
> >  	}
> >  
> > @@ -4270,10 +4270,11 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
> >  
> >  	return NETDEV_TX_OK;
> >  
> > -err_dma_1:
> > +err_dma_2:
> >  	rtl8169_unmap_tx_skb(tp, entry);
> > -err_dma_0:
> > +err_dma_1:
> >  	dev_kfree_skb_any(skb);
> > +err_dma_0:
> >  	dev->stats.tx_dropped++;
> >  	return NETDEV_TX_OK;
> >  
> > 
> 

Ok, i see taht __skb_put_padto(skb, padto, false) isn't free skb on error.

Thanks.