ieee802154: Add support for limiting the number of associated devices

Coordinators may refuse associations. We need a user input for
that. Let's add a new netlink command which can provide a maximum number
of devices we accept to associate with as a first step. Later, we could
also forward the request to userspace and check whether the association
should be accepted or not.
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/20230927181214.129346-9-miquel.raynal@bootlin.com

include/net/cfg802154.h

@@ -506,6 +506,7 @@ struct wpan_dev {
 	struct mutex association_lock;
 	struct ieee802154_pan_device *parent;
 	struct list_head children;
+	unsigned int max_associations;
 };
 
 #define to_phy(_dev)	container_of(_dev, struct wpan_phy, dev)
@@ -583,6 +584,13 @@ struct ieee802154_pan_device *
 cfg802154_device_is_child(struct wpan_dev *wpan_dev,
 			  struct ieee802154_addr *target);
 
+/**
+ * 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
+ */
+void 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
  * @wpan_dev: the wpan device

include/net/nl802154.h

@@ -80,6 +80,7 @@ enum nl802154_commands {
 	NL802154_CMD_STOP_BEACONS,
 	NL802154_CMD_ASSOCIATE,
 	NL802154_CMD_DISASSOCIATE,
+	NL802154_CMD_SET_MAX_ASSOCIATIONS,
 
 	/* add new commands above here */
 
@@ -149,6 +150,7 @@ enum nl802154_attrs {
 	NL802154_ATTR_SCAN_DURATION,
 	NL802154_ATTR_SCAN_DONE_REASON,
 	NL802154_ATTR_BEACON_INTERVAL,
+	NL802154_ATTR_MAX_ASSOCIATIONS,
 
 	/* add attributes here, update the policy in nl802154.c */
 

net/ieee802154/core.c

@@ -295,6 +295,7 @@ static int cfg802154_netdev_notifier_call(struct notifier_block *nb,
 		rdev->devlist_generation++;
 		mutex_init(&wpan_dev->association_lock);
 		INIT_LIST_HEAD(&wpan_dev->children);
+		wpan_dev->max_associations = SZ_16K;
 
 		wpan_dev->netdev = dev;
 		break;

net/ieee802154/nl802154.c

@@ -234,6 +234,7 @@ static const struct nla_policy nl802154_policy[NL802154_ATTR_MAX+1] = {
 				 NL802154_SCAN_DONE_REASON_ABORTED),
 	[NL802154_ATTR_BEACON_INTERVAL] =
 		NLA_POLICY_MAX(NLA_U8, IEEE802154_ACTIVE_SCAN_DURATION),
+	[NL802154_ATTR_MAX_ASSOCIATIONS] = { .type = NLA_U32 },
 
 #ifdef CONFIG_IEEE802154_NL802154_EXPERIMENTAL
 	[NL802154_ATTR_SEC_ENABLED] = { .type = NLA_U8, },
@@ -1696,6 +1697,26 @@ static int nl802154_disassociate(struct sk_buff *skb, struct genl_info *info)
 	return 0;
 }
 
+static int nl802154_set_max_associations(struct sk_buff *skb, struct genl_info *info)
+{
+	struct net_device *dev = info->user_ptr[1];
+	struct wpan_dev *wpan_dev = dev->ieee802154_ptr;
+	unsigned int max_assoc;
+
+	if (!info->attrs[NL802154_ATTR_MAX_ASSOCIATIONS]) {
+		NL_SET_ERR_MSG(info->extack, "No maximum number of association given");
+		return -EINVAL;
+	}
+
+	max_assoc = nla_get_u32(info->attrs[NL802154_ATTR_MAX_ASSOCIATIONS]);
+
+	mutex_lock(&wpan_dev->association_lock);
+	cfg802154_set_max_associations(wpan_dev, max_assoc);
+	mutex_unlock(&wpan_dev->association_lock);
+
+	return 0;
+}
+
 #ifdef CONFIG_IEEE802154_NL802154_EXPERIMENTAL
 static const struct nla_policy nl802154_dev_addr_policy[NL802154_DEV_ADDR_ATTR_MAX + 1] = {
 	[NL802154_DEV_ADDR_ATTR_PAN_ID] = { .type = NLA_U16 },
@@ -2833,6 +2854,13 @@ static const struct genl_ops nl802154_ops[] = {
 				  NL802154_FLAG_CHECK_NETDEV_UP |
 				  NL802154_FLAG_NEED_RTNL,
 	},
+	{
+		.cmd = NL802154_CMD_SET_MAX_ASSOCIATIONS,
+		.doit = nl802154_set_max_associations,
+		.flags = GENL_ADMIN_PERM,
+		.internal_flags = NL802154_FLAG_NEED_NETDEV |
+				  NL802154_FLAG_NEED_RTNL,
+	},
 #ifdef CONFIG_IEEE802154_NL802154_EXPERIMENTAL
 	{
 		.cmd = NL802154_CMD_SET_SEC_PARAMS,

net/ieee802154/pan.c

@@ -93,3 +93,11 @@ __le16 cfg802154_get_free_short_addr(struct wpan_dev *wpan_dev)
 	return addr;
 }
 EXPORT_SYMBOL_GPL(cfg802154_get_free_short_addr);
+
+void cfg802154_set_max_associations(struct wpan_dev *wpan_dev, unsigned int max)
+{
+	lockdep_assert_held(&wpan_dev->association_lock);
+
+	wpan_dev->max_associations = max;
+}
+EXPORT_SYMBOL_GPL(cfg802154_set_max_associations);