[PATCH net-next v2] net: airoha: Validate egress gdm port in airoha_ppe_foe_entry_prepare()

[Lorenzo Bianconi]

> > Fix the issue validating egress gdm port in airoha_ppe_foe_entry_prepare
> > routine.
> 
> A more interesting question is, why do you see an invalid port? Is the
> hardware broken? Something not correctly configured? Are you just
> papering over the crack?
> 
> > -static int airoha_ppe_foe_entry_prepare(struct airoha_foe_entry *hwe,
> > +static int airoha_ppe_foe_entry_prepare(struct airoha_eth *eth,
> > +					struct airoha_foe_entry *hwe,
> >  					struct net_device *dev, int type,
> >  					struct airoha_flow_data *data,
> >  					int l4proto)
> > @@ -224,6 +225,11 @@ static int airoha_ppe_foe_entry_prepare(struct airoha_foe_entry *hwe,
> >  	if (dev) {
> >  		struct airoha_gdm_port *port = netdev_priv(dev);
> 
> If port is invalid, is dev also invalid? And if dev is invalid, could
> dereferencing it to get priv cause an opps?

I do not think this is a hw problem. Running bidirectional high load traffic,
I got the sporadic crash reported above. In particular, netfilter runs
airoha_ppe_flow_offload_replace() providing the egress net_device pointer used
in airoha_ppe_foe_entry_prepare(). Debugging with gdb, I discovered the system
crashes dereferencing port pointer in airoha_ppe_foe_entry_prepare() (even if
dev pointer is not NULL). Adding this sanity check makes the system stable.
Please note a similar check is available even in mtk driver [0].

Regards,
Lorenzo

[0] https://github.com/torvalds/linux/blob/master/drivers/net/ethernet/mediatek/mtk_ppe_offload.c#L220

> 
> 	Andrew
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