[PATCH 09/10] wifi: mt76: reject out-of-range link ids in mt76_vif_link()

mt76_vif_link() indexes mvif->link[] without validating link_id, but
callers pass mvif->deflink_id / msta->deflink_id, which hold
IEEE80211_LINK_UNSPECIFIED (0xf) until the first link has been added.
Since IEEE80211_MLD_MAX_NUM_LINKS is 15, that reads one element past the
end of the array, aliasing mt76_vif_data.offchannel_link.

Reachable via mt7996_set_tsf()/mt7996_offset_tsf() and
mt7996_net_fill_forward_path(). Bounds check link_id and return NULL,
matching mt7996_sta_link() and mt7996_sta_link_protected().

Fixes: a9384b36a42a ("wifi: mt76: mt7996: rework set/get_tsf callabcks to support MLO")
Signed-off-by: Felix Fietkau <[email protected]>
---
 drivers/net/wireless/mediatek/mt76/mt76.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
index dc160d9ae537..61ef1b80feb8 100644
--- a/drivers/net/wireless/mediatek/mt76/mt76.h
+++ b/drivers/net/wireless/mediatek/mt76/mt76.h
@@ -2131,6 +2131,9 @@ mt76_vif_link(struct mt76_dev *dev, struct ieee80211_vif *vif, int link_id)
 	if (!link_id)
 		return mlink;
 
+	if (link_id >= IEEE80211_MLD_MAX_NUM_LINKS)
+		return NULL;
+
 	return mt76_dereference(mvif->link[link_id], dev);
 }
 
-- 
2.53.0