[bug report] wifi: mt76: Check link_conf pointer in mt76_connac_mcu_sta_basic_tlv()

[Shayne Chen]

On Fri, 2025-03-21 at 17:29 +0100, Lorenzo Bianconi wrote:
> > Hello Shayne Chen,
> > 
> > This is a semi-automatic email about new static checker warnings.
> > 
> > Commit 9890624c1b39 ("wifi: mt76: Check link_conf pointer in
> > mt76_connac_mcu_sta_basic_tlv()") from Mar 11, 2025, leads to the
> > following Smatch complaint:
> > 
> >     drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.c:394
> > mt76_connac_mcu_sta_basic_tlv()
> >     warn: variable dereferenced before check 'link_conf' (see line
> > 376)
> > 
> > drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.c
> >    375	{
> >    376		struct ieee80211_vif *vif = link_conf->vif;
> >                                             ^^^^^^^^^^^^^^
> 
> Reviewing the codebase, it seems to me it is safe to revert
> 9890624c1b39 since
> link_conf is always not NULL running mt76_connac_mcu_sta_basic_tlv().
> @Shayne Chen: agree?
> 
link_conf won't be NULL in this function at the moment, but it could be
NULL after adding "MLO reconfiguration" support. So in our internal
tree, we directly pass struct ieee80211_vif to this function.

Both methods are fine to me, what do you think?

Regards,
Shayne

> Regards,
> Lorenzo
> 
> > Dereferenced.
> > 
> >    377		struct sta_rec_basic *basic;
> >    378		struct tlv *tlv;
> >    379		int conn_type;
> >    380	
> >    381		tlv = mt76_connac_mcu_add_tlv(skb, STA_REC_BASIC,
> > sizeof(*basic));
> >    382	
> >    383		basic = (struct sta_rec_basic *)tlv;
> >    384		basic->extra_info = cpu_to_le16(EXTRA_INFO_VER);
> >    385	
> >    386		if (newly && conn_state != CONN_STATE_DISCONNECT)
> >    387			basic->extra_info |=
> > cpu_to_le16(EXTRA_INFO_NEW);
> >    388		basic->conn_state = conn_state;
> >    389	
> >    390		if (!link_sta) {
> >    391			basic->conn_type =
> > cpu_to_le32(CONNECTION_INFRA_BC);
> >    392	
> >    393			if (vif->type == NL80211_IFTYPE_STATION &&
> >    394			    link_conf &&
> > !is_zero_ether_addr(link_conf->bssid)) {
> >                             ^^^^^^^^^
> > The patch adds a NULL dereference but it's too late.
> > 
> >    395				memcpy(basic->peer_addr,
> > link_conf->bssid, ETH_ALEN);
> >    396				basic->aid = cpu_to_le16(vif-
> > >cfg.aid);
> > 
> > regards,
> > dan carpenter
> >