Re: [PATCH RFC/RFT net-next v2 1/5] net: dsa: deny bridge VLAN with existing 8021q upper on any port

Jonas Gorski
2025-12-01T19:52:45Z

Hi,

On Mon, Dec 1, 2025 at 3:48 PM Simon Horman <horms@kernel.org> wrote:
>
> On Mon, Dec 01, 2025 at 11:28:13AM +0100, Jonas Gorski wrote:
>
> ...
>
> > diff --git a/net/dsa/user.c b/net/dsa/user.c
> > index f59d66f0975d..fa1fe0f1493a 100644
> > --- a/net/dsa/user.c
> > +++ b/net/dsa/user.c
> > @@ -653,21 +653,30 @@ static int dsa_user_port_attr_set(struct net_device *dev, const void *ctx,
> >
> > /* Must be called under rcu_read_lock() */
> > static int
> > -dsa_user_vlan_check_for_8021q_uppers(struct net_device *user,
> > +dsa_user_vlan_check_for_8021q_uppers(struct dsa_port *dp,
> > const struct switchdev_obj_port_vlan *vlan)
> > {
> > - struct net_device *upper_dev;
> > - struct list_head *iter;
> > + struct dsa_switch *ds = dp->ds;
> > + struct dsa_port *other_dp;
> >
> > - netdev_for_each_upper_dev_rcu(user, upper_dev, iter) {
> > - u16 vid;
> > + dsa_switch_for_each_user_port(other_dp, ds) {
> > + struct net_device *user = other_dp->user;
>
> Hi Jonas,
>
> The AI robot is concerned that user may be NULL here.
> And I can't convince myself that cannot be the case.
>
> Could you take a look?
>
> https://netdev-ai.bots.linux.dev/ai-review.html?id=3d47057e-e740-4b66-9d60-9ec2a7ee92a1#patch-0

At this point it can be NULL. But it being NULL is not an issue, as ...
>
> > + struct net_device *upper_dev;
> > + struct list_head *iter;
> >
> > - if (!is_vlan_dev(upper_dev))
> > + if (!dsa_port_bridge_same(dp, other_dp))
> > continue;

... this condition will filter all cases where it is NULL. For
dsa_port_bridge_same() to return true both ports need to be attached
to a bridge (and to the same bridge), and to be attached to a bridge a
net_device is required, so other_dp->user cannot be NULL. And we only
access user after here.

Best regards,
Jonas