wifi: mac80211: fix vif addr when switching from monitor to station

Since adding support for opting out of virtual monitor support, a zero vif
addr was used to indicate passive vs active monitor to the driver.
This would break the vif->addr when changing the netdev mac address before
switching the interface from monitor to sta mode.
Fix the regression by adding a separate flag to indicate whether vif->addr
is valid.

Reported-by: syzbot+9ea265d998de25ac6a46@syzkaller.appspotmail.com
Fixes: 9d40f7e ("wifi: mac80211: add flag to opt out of virtual monitor support")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://patch.msgid.link/20241115115850.37449-1-nbd@nbd.name
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: nbd168

include/net/mac80211.h

@@ -1987,6 +1987,8 @@ enum ieee80211_neg_ttlm_res {
  * @neg_ttlm: negotiated TID to link mapping info.
  *	see &struct ieee80211_neg_ttlm.
  * @addr: address of this interface
+ * @addr_valid: indicates if the address is actively used. Set to false for
+ *	passive monitor interfaces, true in all other cases.
  * @p2p: indicates whether this AP or STA interface is a p2p
  *	interface, i.e. a GO or p2p-sta respectively
  * @netdev_features: tx netdev features supported by the hardware for this
@@ -2026,6 +2028,7 @@ struct ieee80211_vif {
 	u16 valid_links, active_links, dormant_links, suspended_links;
 	struct ieee80211_neg_ttlm neg_ttlm;
 	u8 addr[ETH_ALEN] __aligned(2);
+	bool addr_valid;
 	bool p2p;
 
 	u8 cab_queue;

net/mac80211/iface.c

@@ -278,13 +278,8 @@ static int _ieee80211_change_mac(struct ieee80211_sub_if_data *sdata,
 	ret = eth_mac_addr(sdata->dev, sa);
 
 	if (ret == 0) {
-		if (check_dup) {
-			memcpy(sdata->vif.addr, sa->sa_data, ETH_ALEN);
-			ether_addr_copy(sdata->vif.bss_conf.addr, sdata->vif.addr);
-		} else {
-			memset(sdata->vif.addr, 0, ETH_ALEN);
-			memset(sdata->vif.bss_conf.addr, 0, ETH_ALEN);
-		}
+		memcpy(sdata->vif.addr, sa->sa_data, ETH_ALEN);
+		ether_addr_copy(sdata->vif.bss_conf.addr, sdata->vif.addr);
 	}
 
 	/* Regardless of eth_mac_addr() return we still want to add the
@@ -1323,6 +1318,8 @@ int ieee80211_do_open(struct wireless_dev *wdev, bool coming_up)
 		}
 	}
 
+	sdata->vif.addr_valid = sdata->vif.type != NL80211_IFTYPE_MONITOR ||
+				(sdata->u.mntr.flags & MONITOR_FLAG_ACTIVE);
 	switch (sdata->vif.type) {
 	case NL80211_IFTYPE_AP_VLAN:
 		/* no need to tell driver, but set carrier and chanctx */