mptcp: add netlink pm addr entry refcount

This patch adds the refcount of address entry in netlink PM. Initiate
'refcont' of every address entry to 1.

Increase this refcount counter when a subflow connecting or an address
signaling in mptcp_pm_nl_add_addr_doit(), fill_local_addresses_vec() and
mptcp_pm_create_subflow_or_signal_addr().

Decrease it when deleting an address in mptcp_pm_nl_del_addr_doit().
When the counter reaches 1, then free this entry.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>

net/mptcp/pm_netlink.c

@@ -598,8 +598,10 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 			continue;
 
 		spin_unlock_bh(&msk->pm.lock);
-		for (i = 0; i < nr; i++)
-			__mptcp_subflow_connect(sk, &local->addr, &addrs[i]);
+		for (i = 0; i < nr; i++) {
+			if (refcount_inc_not_zero(&local->refcnt))
+				__mptcp_subflow_connect(sk, &local->addr, &addrs[i]);
+		}
 		spin_lock_bh(&msk->pm.lock);
 	}
 	mptcp_pm_nl_check_work_pending(msk);
@@ -639,7 +641,8 @@ static unsigned int fill_local_addresses_vec(struct mptcp_sock *msk,
 		if (!mptcp_pm_addr_families_match(sk, &entry->addr, remote))
 			continue;
 
-		if (msk->pm.subflows < subflows_max) {
+		if (msk->pm.subflows < subflows_max &&
+		    refcount_inc_not_zero(&entry->refcnt)) {
 			msk->pm.subflows++;
 			addrs[i++] = entry->addr;
 		}
@@ -1088,6 +1091,7 @@ int mptcp_pm_nl_get_local_id(struct mptcp_sock *msk, struct mptcp_addr_info *skc
 	entry->ifindex = 0;
 	entry->flags = MPTCP_PM_ADDR_FLAG_IMPLICIT;
 	entry->lsk = NULL;
+	refcount_set(&entry->refcnt, 1);
 	ret = mptcp_pm_nl_append_new_local_addr(pernet, entry, true);
 	if (ret < 0)
 		kfree(entry);
@@ -1327,6 +1331,7 @@ int mptcp_pm_nl_add_addr_doit(struct sk_buff *skb, struct genl_info *info)
 	}
 
 	*entry = addr;
+	refcount_set(&entry->refcnt, 1);
 	if (entry->addr.port) {
 		ret = mptcp_pm_nl_create_listen_socket(skb->sk, entry);
 		if (ret) {
@@ -1341,7 +1346,8 @@ int mptcp_pm_nl_add_addr_doit(struct sk_buff *skb, struct genl_info *info)
 		goto out_free;
 	}
 
-	mptcp_nl_add_subflow_or_signal_addr(sock_net(skb->sk));
+	if (refcount_inc_not_zero(&entry->refcnt))
+		mptcp_nl_add_subflow_or_signal_addr(sock_net(skb->sk));
 	return 0;
 
 out_free:
@@ -1480,6 +1486,7 @@ int mptcp_pm_nl_del_addr_doit(struct sk_buff *skb, struct genl_info *info)
 	struct nlattr *attr = info->attrs[MPTCP_PM_ENDPOINT_ADDR];
 	struct pm_nl_pernet *pernet = genl_info_pm_nl(info);
 	struct mptcp_pm_addr_entry addr, *entry;
+	bool release_entry = false;
 	unsigned int addr_max;
 	int ret;
 
@@ -1511,14 +1518,21 @@ int mptcp_pm_nl_del_addr_doit(struct sk_buff *skb, struct genl_info *info)
 		WRITE_ONCE(pernet->local_addr_max, addr_max - 1);
 	}
 
-	pernet->addrs--;
-	list_del_rcu(&entry->list);
-	__clear_bit(entry->addr.id, pernet->id_bitmap);
+	if (refcount_dec_not_one(&entry->refcnt) &&
+	    refcount_read(&entry->refcnt) == 1) {
+		pernet->addrs--;
+		list_del_rcu(&entry->list);
+		__clear_bit(entry->addr.id, pernet->id_bitmap);
+		release_entry = true;
+	}
 	spin_unlock_bh(&pernet->lock);
 
 	mptcp_nl_remove_subflow_and_signal_addr(sock_net(skb->sk), entry);
 	synchronize_rcu();
-	__mptcp_pm_release_addr_entry(entry);
+	if (release_entry)
+		__mptcp_pm_release_addr_entry(entry);
+	else
+		entry->flags |= MPTCP_PM_ADDR_FLAG_IMPLICIT;
 
 	return ret;
 }