netdev - Re: [PATCH net v5] net: stmmac: Prevent DSA tags from breaking COE

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Date: Tue, 16 Jan 2024 13:14:15 +0100 (CET)
From: Romain Gantois <romain.gantois@...tlin.com>
To: Jakub Kicinski <kuba@...nel.org>
cc: Romain Gantois <romain.gantois@...tlin.com>, 
    Alexandre Torgue <alexandre.torgue@...s.st.com>, 
    Jose Abreu <joabreu@...opsys.com>, "David S. Miller" <davem@...emloft.net>, 
    Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 
    Maxime Coquelin <mcoquelin.stm32@...il.com>, 
    Miquel Raynal <miquel.raynal@...tlin.com>, 
    Maxime Chevallier <maxime.chevallier@...tlin.com>, 
    Sylvain Girard <sylvain.girard@...com>, 
    Pascal EBERHARD <pascal.eberhard@...com>, 
    Richard Tresidder <rtresidd@...ctromag.com.au>, 
    Linus Walleij <linus.walleij@...aro.org>, 
    Vladimir Oltean <olteanv@...il.com>, Andrew Lunn <andrew@...n.ch>, 
    Thomas Petazzoni <thomas.petazzoni@...tlin.com>, netdev@...r.kernel.org, 
    linux-stm32@...md-mailman.stormreply.com, 
    linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org, 
    Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net v5] net: stmmac: Prevent DSA tags from breaking COE

Hi Jakub,

On Fri, 12 Jan 2024, Jakub Kicinski wrote:

> > @@ -4997,7 +5020,7 @@ static void stmmac_dispatch_skb_zc(struct stmmac_priv *priv, u32 queue,
> >  	stmmac_rx_vlan(priv->dev, skb);
> >  	skb->protocol = eth_type_trans(skb, priv->dev);
> >  
> > -	if (unlikely(!coe))
> > +	if (unlikely(!coe) || !stmmac_has_ip_ethertype(skb))
> 
> The lack of Rx side COE checking in this driver is kinda crazy.
> Looking at enh_desc_coe_rdes0() it seems like RDES0_FRAME_TYPE
> may be the indication we need here? 

I don't think that RDES0_FRAME_TYPE would be enough, at least not on its own. 
That bit is set by checking the length/ethertype field to see if is an 
Ethernet II frame or an IEEE802.3 frame. But even Ethernet II frames with non-IP 
ethertypes will not be checksummed. Also protocols with a non-fixed ethertype 
field such as DSA_TAG_PROTO could trigger the bit, or not, depending on what 
they put in the DSA tag.

--
Romain Gantois, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com