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

[sashiko-bot@kernel.org]

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
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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?

> +
> +	return skb;
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260923-devel-vstrassheim-soce-dsa-ml-v3-0-ddebafcb9ba7@linutronix.de?part=4