netdev - Re: [PATCH 1/4] net: dsa: add support for the SMSC-LAN9303 tagging format

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Message-Id: <201704061536.27164.jbe@pengutronix.de>
Date:   Thu, 6 Apr 2017 15:36:26 +0200
From:   Juergen Borleis <jbe@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        f.fainelli@...il.com, kernel@...gutronix.de,
        vivien.didelot@...oirfairelinux.com, davem@...emloft.net
Subject: Re: [PATCH 1/4] net: dsa: add support for the SMSC-LAN9303 tagging format

Hi Andrew,

On Wednesday 05 April 2017 19:10:01 Andrew Lunn wrote:
> [...]
> > +static int lan9303_rcv(struct sk_buff *skb, struct net_device *dev,
> > +		       struct packet_type *pt, struct net_device *orig_dev)
> > +{
> > +	u16 *lan9303_tag;
> > +	struct dsa_switch_tree *dst = dev->dsa_ptr;
> > +	struct dsa_switch *ds = dst->ds[0];
> > +	unsigned int source_port;
> > +
> > +	if (unlikely(!dst)) {
> > +		dev_warn_ratelimited(&dev->dev, "Dropping packet, due to missing switch tree device\n");
> > +		goto out_drop; 
> > +	}
>
> By the time you get here, you have already dereferenced dst, in order
> to get ds. So this is pointless.

Ups! Thanks! Fixed in v2.

> > +	lan9303_tag = (u16 *)(skb->data - 2);
> > +
> > +	if (lan9303_tag[0] != htons(0x8100)) {
> > +		dev_warn_ratelimited(&dev->dev, "Dropping packet due to invalid VLAN marker\n");
> > +		goto out_drop; 
> > +	}
>
> In the transmit function, you use ETH_P_8021Q, please do so here as
> well.

Done in v2.

> > +	source_port = ntohs(lan9303_tag[1]) & 0x3;
> > +
> > +	if (source_port >= DSA_MAX_PORTS) {
> > +		dev_warn_ratelimited(&dev->dev, "Dropping packet due to invalid source port\n");
> > +		goto out_drop; 
> > +	}
>
> You can be more specific here. For this hardware, > 3 is invalid and
> should be dropped. If we later add other chips which have more ports,
> we can relax this check then.

Done in v2.

> > +	/* remove the special VLAN tag between the MAC addresses
> > +	 * and the current ethertype field.
> > +	 */
> > +	skb_pull_rcsum(skb, 2 + 2);
> > +	memmove(skb->data - ETH_HLEN, skb->data - (ETH_HLEN + LAN9303_TAG_LEN),
> > +		2 * ETH_ALEN); 
> > +	skb_push(skb, ETH_HLEN);
>
> Do you need to do anything with the checksum here? Other tagging
> protocols do.

Don't know exactly what you are meaning here. For me it does the same like
the qca_tag_rcv() function in tag_qca.c does.

Juergen

-- 
Pengutronix e.K.                             | Juergen Borleis             |
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