mptcp: check addrs list in userspace_pm_get_local_id

Before adding a new entry in mptcp_userspace_pm_get_local_id(), it's
better to check whether this address is already in userspace pm local
address list. If it's in the list, no need to add a new entry, just
return it's address ID and use this address.

Fixes: 8b201370 ("mptcp: read attributes of addr entries managed by userspace PMs")
Cc: stable@vger.kernel.org
Signed-off-by: Geliang Tang <geliang.tang@linux.dev>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/pm_userspace.c

@@ -130,10 +130,21 @@ int mptcp_userspace_pm_get_flags_and_ifindex_by_id(struct mptcp_sock *msk,
 int mptcp_userspace_pm_get_local_id(struct mptcp_sock *msk,
 				    struct mptcp_addr_info *skc)
 {
-	struct mptcp_pm_addr_entry new_entry;
+	struct mptcp_pm_addr_entry *entry = NULL, *e, new_entry;
 	__be16 msk_sport =  ((struct inet_sock *)
 			     inet_sk((struct sock *)msk))->inet_sport;
 
+	spin_lock_bh(&msk->pm.lock);
+	list_for_each_entry(e, &msk->pm.userspace_pm_local_addr_list, list) {
+		if (mptcp_addresses_equal(&e->addr, skc, false)) {
+			entry = e;
+			break;
+		}
+	}
+	spin_unlock_bh(&msk->pm.lock);
+	if (entry)
+		return entry->addr.id;
+
 	memset(&new_entry, 0, sizeof(struct mptcp_pm_addr_entry));
 	new_entry.addr = *skc;
 	new_entry.addr.id = 0;