wifi: mac80211: do not use old MBSSID elements

When userspace brings down and deletes a non-transmitted profile,
it is expected to send a new updated Beacon template for the
transmitted profile of that multiple BSSID (MBSSID) group which
does not include the removed profile in MBSSID element. This
update comes via NL80211_CMD_SET_BEACON.

Such updates work well as long as the group continues to have at
least one non-transmitted profile as NL80211_ATTR_MBSSID_ELEMS
is included in the new Beacon template.

But when the last non-trasmitted profile is removed, it still
gets included in Beacon templates sent to driver. This happens
because when no MBSSID elements are sent by the userspace,
ieee80211_assign_beacon() ends up using the element stored from
earlier Beacon template.

Do not copy old MBSSID elements, instead userspace should always
include these when applicable.

Fixes: 2b3171c ("mac80211: MBSSID beacon handling in AP mode")
Signed-off-by: Aloka Dixit <aloka.dixit@oss.qualcomm.com>
Link: https://patch.msgid.link/20251215174656.2866319-2-aloka.dixit@oss.qualcomm.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: Aloka Dixit

net/mac80211/cfg.c

@@ -1345,7 +1345,6 @@ ieee80211_assign_beacon(struct ieee80211_sub_if_data *sdata,
 
 	size = sizeof(*new) + new_head_len + new_tail_len;
 
-	/* new or old multiple BSSID elements? */
 	if (params->mbssid_ies) {
 		mbssid = params->mbssid_ies;
 		size += struct_size(new->mbssid_ies, elem, mbssid->cnt);
@@ -1355,15 +1354,6 @@ ieee80211_assign_beacon(struct ieee80211_sub_if_data *sdata,
 		}
 		size += ieee80211_get_mbssid_beacon_len(mbssid, rnr,
 							mbssid->cnt);
-	} else if (old && old->mbssid_ies) {
-		mbssid = old->mbssid_ies;
-		size += struct_size(new->mbssid_ies, elem, mbssid->cnt);
-		if (old && old->rnr_ies) {
-			rnr = old->rnr_ies;
-			size += struct_size(new->rnr_ies, elem, rnr->cnt);
-		}
-		size += ieee80211_get_mbssid_beacon_len(mbssid, rnr,
-							mbssid->cnt);
 	}
 
 	new = kzalloc(size, GFP_KERNEL);