Re: [PATCH net-next v10 1/9] net: dsa: add tag driver for LAN9645X

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Adding an out-of-band VLAN tag without checking for and popping an existing payload tag results in double-tagged frames.
--

--- Patch [1]: [PATCH net-next v10 1/9] net: dsa: add tag driver for LAN9645X ---
commit 3fca3b09e95a3eeee247c89f8ecdf602074e9506
Author: Jens Emil Schulz Østergaard <jensemil.schulzostergaard@microchip.com>

net: dsa: add tag driver for LAN9645X

This commit adds a DSA tag driver for the LAN9645x family of switches. It
configures an NPI port to use a 16-byte long prefix on extraction and no
prefix on injection, prepending an internal frame header (IFH) to transmit
critical data.

> diff --git a/net/dsa/tag_lan9645x.c b/net/dsa/tag_lan9645x.c
> new file mode 100644
> index 0000000000000..2692c7ad56cbc
> --- /dev/null
> +++ b/net/dsa/tag_lan9645x.c
[ ... ]
> +static struct sk_buff *lan9645x_rcv(struct sk_buff *skb,
> +				    struct net_device *ndev)
> +{
[ ... ]
> +	/* While we have REW_PORT_NO_REWRITE=0 on the NPI port, we still disable
> +	 * port VLAN tagging with REW_TAG_CFG. Any classified VID, different
> +	 * from a VID in the frame, will not be written to the frame, but is
> +	 * only communicated via the IFH. So for VLAN-aware ports we add the IFH
> +	 * vlan to the skb.
> +	 */
> +	dp = dsa_user_to_port(skb->dev);
> +	vlan_tpid = tag_type ? ETH_P_8021AD : ETH_P_8021Q;
> +
> +	if (dsa_port_is_vlan_filtering(dp) && vlan_tci) {
> +		u16 port_pvid = 0;
> +
> +		br_vlan_get_pvid_rcu(skb->dev, &port_pvid);
> +
> +		if ((vlan_tci & VLAN_VID_MASK) != port_pvid)

[Severity: High]
Does this code result in double-tagged frames?

If the hardware delivers the frame without stripping the in-band tag because
port VLAN rewrite is disabled, calling __vlan_hwaccel_put_tag() here adds an
out-of-band tag while leaving the original in-band tag intact in the payload.
This would cause the network stack to process a single 802.1Q tagged frame
from the wire as a Q-in-Q double-tagged frame.

Should lan9645x_rcv() pop the existing payload tag (for example, using
__skb_vlan_pop()) before adding the out-of-band tag to avoid duplicating it?

> +			__vlan_hwaccel_put_tag(skb, htons(vlan_tpid), vlan_tci);
> +	}
> +
> +	return skb;
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260713-dsa_lan9645x_switch_driver_base-v10-0-a4886a08fb15@microchip.com?part=1