mac802154: Avoid new associations while disassociating

While disassociating from a PAN ourselves, let's set the maximum number
of associations temporarily to zero to be sure no new device tries to
associate with us.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Stefan Schmidt <stefan@datenfreihafen.org>
Acked-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/linux-wpan/20231128111655.507479-6-miquel.raynal@bootlin.com

include/net/cfg802154.h

@@ -589,8 +589,10 @@ cfg802154_device_is_child(struct wpan_dev *wpan_dev,
  * cfg802154_set_max_associations - Limit the number of future associations
  * @wpan_dev: the wpan device
  * @max: the maximum number of devices we accept to associate
+ * @return: the old maximum value
  */
-void cfg802154_set_max_associations(struct wpan_dev *wpan_dev, unsigned int max);
+unsigned int cfg802154_set_max_associations(struct wpan_dev *wpan_dev,
+					    unsigned int max);
 
 /**
  * cfg802154_get_free_short_addr - Get a free address among the known devices

net/ieee802154/pan.c

@@ -94,10 +94,16 @@ __le16 cfg802154_get_free_short_addr(struct wpan_dev *wpan_dev)
 }
 EXPORT_SYMBOL_GPL(cfg802154_get_free_short_addr);
 
-void cfg802154_set_max_associations(struct wpan_dev *wpan_dev, unsigned int max)
+unsigned int cfg802154_set_max_associations(struct wpan_dev *wpan_dev,
+					    unsigned int max)
 {
+	unsigned int old_max;
+
 	lockdep_assert_held(&wpan_dev->association_lock);
 
+	old_max = wpan_dev->max_associations;
 	wpan_dev->max_associations = max;
+
+	return old_max;
 }
 EXPORT_SYMBOL_GPL(cfg802154_set_max_associations);

net/mac802154/cfg.c

@@ -389,6 +389,7 @@ static int mac802154_disassociate_from_parent(struct wpan_phy *wpan_phy,
 	struct ieee802154_local *local = wpan_phy_priv(wpan_phy);
 	struct ieee802154_pan_device *child, *tmp;
 	struct ieee802154_sub_if_data *sdata;
+	unsigned int max_assoc;
 	u64 eaddr;
 	int ret;
 
@@ -397,6 +398,7 @@ static int mac802154_disassociate_from_parent(struct wpan_phy *wpan_phy,
 	/* Start by disassociating all the children and preventing new ones to
 	 * attempt associations.
 	 */
+	max_assoc = cfg802154_set_max_associations(wpan_dev, 0);
 	list_for_each_entry_safe(child, tmp, &wpan_dev->children, node) {
 		ret = mac802154_send_disassociation_notif(sdata, child,
 							  IEEE802154_COORD_WISHES_DEVICE_TO_LEAVE);
@@ -429,14 +431,17 @@ static int mac802154_disassociate_from_parent(struct wpan_phy *wpan_phy,
 	if (local->hw.flags & IEEE802154_HW_AFILT) {
 		ret = drv_set_pan_id(local, wpan_dev->pan_id);
 		if (ret < 0)
-			return ret;
+			goto reset_mac_assoc;
 
 		ret = drv_set_short_addr(local, wpan_dev->short_addr);
 		if (ret < 0)
-			return ret;
+			goto reset_mac_assoc;
 	}
 
-	return 0;
+reset_mac_assoc:
+	cfg802154_set_max_associations(wpan_dev, max_assoc);
+
+	return ret;
 }
 
 static int mac802154_disassociate_child(struct wpan_phy *wpan_phy,