Re: [PATCHv2 net] hsr: use proper locking when iterating over ports

[Hangbin Liu <liuhangbin@gmail.com>]

On Thu, Aug 28, 2025 at 11:19:11AM +0200, Paolo Abeni wrote:
> On 8/27/25 11:33 AM, Hangbin Liu wrote:
> > @@ -672,9 +672,13 @@ struct net_device *hsr_get_port_ndev(struct net_device *ndev,
> >  	struct hsr_priv *hsr = netdev_priv(ndev);
> >  	struct hsr_port *port;
> >  
> > +	rcu_read_lock();
> >  	hsr_for_each_port(hsr, port)
> > -		if (port->type == pt)
> > +		if (port->type == pt) {
> > +			rcu_read_unlock();
> >  			return port->dev;
> 
> This is not good enough. At this point accessing `port` could still
> cause UaF;
> 
> The only callers, in icssg_prueth_hsr_{add,del}_mcast(), can be either
> under the RTNL lock or not. A safer option would be acquiring a
> reference on dev before releasing the rcu lock and let the caller drop
> such reference

OK, thanks for the suggestion.

> 
> > +		}
> > +	rcu_read_unlock();
> >  	return NULL;
> >  }
> >  EXPORT_SYMBOL(hsr_get_port_ndev);
> > diff --git a/net/hsr/hsr_main.c b/net/hsr/hsr_main.c
> > index 192893c3f2ec..eec6e20a8494 100644
> > --- a/net/hsr/hsr_main.c
> > +++ b/net/hsr/hsr_main.c
> > @@ -22,9 +22,13 @@ static bool hsr_slave_empty(struct hsr_priv *hsr)
> >  {
> >  	struct hsr_port *port;
> >  
> > +	rcu_read_lock();
> >  	hsr_for_each_port(hsr, port)
> > -		if (port->type != HSR_PT_MASTER)
> > +		if (port->type != HSR_PT_MASTER) {
> > +			rcu_read_unlock();
> >  			return false;
> > +		}
> > +	rcu_read_unlock();
> >  	return true;
> >  }
> 
> AFAICS the only caller of this helper is under the RTNL lock

Thanks, sometimes I not very sure if the caller is under RTNL lock or not.
Is there a good way to check this?

> 
> > @@ -134,9 +138,13 @@ struct hsr_port *hsr_port_get_hsr(struct hsr_priv *hsr, enum hsr_port_type pt)
> >  {
> >  	struct hsr_port *port;
> >  
> > +	rcu_read_lock();
> >  	hsr_for_each_port(hsr, port)
> > -		if (port->type == pt)
> > +		if (port->type == pt) {
> > +			rcu_read_unlock();
> >  			return port;
> 
> The above is not enough.
> 
> AFAICS some/most caller are already either under the RTNL lock or the
> rcu lock.
> 
> I think it would be better rename the hsr_for_each_port_rtnl() helper to
> hsr_for_each_port_rcu(), retaining the current semantic, use it here,
> and fix the caller as needed.

Do you mean to modify like

 #define hsr_for_each_port(hsr, port) \
        list_for_each_entry_rcu((port), &(hsr)->ports, port_list)

+#define hsr_for_each_port_rcu(hsr, port) \
+       list_for_each_entry_rcu((port), &(hsr)->ports, port_list, lockdep_rtnl_is_held())


I'm not sure if the naming is clear. e.g. rcu_dereference_rtnl() also use rtnl
suffix to check if rtnl is held.

> 
> It will be useful to somehow split the patch in a series, as it's
> already quite big and will increase even more.

OK.

Thanks
Hangbin
> 
> /P
>