Re: [PATCH net-next v3 4/8] net: dsa: Add tag handling for SoC-e switches

[Vasilij Strassheim <v.strassheim@linutronix.de>]

On Thu, 2026-09-24 at 10:40 +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] net: dsa: tag_sdsa: unsupported VLAN tags left in hwaccel metadata
> --
> 
> commit c9312ab6752036eeab3076e94713c79223982016
> Author: Vasilij Strassheim <v.strassheim@linutronix.de>
> 
> net: dsa: Add tag handling for SoC-e switches
> 
> This commit adds a DSA tag driver for SoC-e switches, which use an 8-byte
> SDSA header carrying frame direction, port, and VLAN metadata. The header
> is inserted between the source MAC address and the original EtherType on
> transmit and receive.
> 
> > diff --git a/net/dsa/tag_sdsa.c b/net/dsa/tag_sdsa.c
> > new file mode 100644
> > index 0000000000000..8cc3fa357be42
> > --- /dev/null
> > +++ b/net/dsa/tag_sdsa.c
> 
> [ ... ]
> 
> > +static struct sk_buff *sdsa_xmit(struct sk_buff *skb, struct net_device *dev)
> > +{
> > +	struct dsa_port *dp = dsa_user_to_port(dev);
> > +	struct sdsa_tag *tag;
> > +	u16 vlan_tci;
> 
> [ ... ]
> 
> > +	/* SDSA carries no TPID, so only encode 802.1Q C-tags. */
> > +	if (skb_vlan_tag_present(skb) &&
> > +	    skb->vlan_proto == htons(ETH_P_8021Q)) {
> > +		vlan_tci = skb_vlan_tag_get(skb);
> > +		__vlan_hwaccel_clear_tag(skb);
> > +		tag->frame_type_port_hi |= SDSA_TAG_VLAN_BIT;
> > +		tag->vlan = cpu_to_be16(vlan_tci);
> > +	} else {
> > +		tag->vlan = 0;
> > +	}
> 
> [Severity: High]
> Does this else branch leave unsupported VLAN tags (like 802.1ad) in the 
> skb's hardware accelerated metadata?
> 
> If a user configures an unsupported VLAN protocol on a DSA user port, the 
> skb will still have skb_vlan_tag_present(skb) set when reaching sdsa_xmit().
> Because this branch does not clear the tag via __vlan_hwaccel_clear_tag(skb),
> the conduit driver's MAC hardware might subsequently insert the remaining 
> VLAN tag at the MAC boundary.
> 
> Could this insertion displace the 8-byte SDSA header just pushed, causing 
> the switch hardware to receive unrecognized frames and drop them?
> 

That's right, I missed it. I will fix it in a similar way to tag_ks8995.

> > +
> > +	return skb;
> > +}
>