mptcp: fix subflow's local_id issues

In mptcp_pm_nl_get_local_id, skc_local is the same as msk_local, so it
always return 0. Thus every subflow's local_id is 0. It's incorrect.

This patch fixed this issue.

Also, we need to ignore the zero address here, like 0.0.0.0 in IPv4. When
we use the zero address as a local address, it means that we can use any
one of the local addresses. The zero address is not a new address, we don't
need to add it to PM, so this patch added a new function address_zero to
check whether an address is the zero address, if it is, we ignore this
address.

Fixes: 01cacb00 ("mptcp: add netlink-based PM")
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/pm_netlink.c

@@ -66,6 +66,16 @@ static bool addresses_equal(const struct mptcp_addr_info *a,
 	return a->port == b->port;
 }
 
+static bool address_zero(const struct mptcp_addr_info *addr)
+{
+	struct mptcp_addr_info zero;
+
+	memset(&zero, 0, sizeof(zero));
+	zero.family = addr->family;
+
+	return addresses_equal(addr, &zero, false);
+}
+
 static void local_address(const struct sock_common *skc,
 			  struct mptcp_addr_info *addr)
 {
@@ -323,10 +333,13 @@ int mptcp_pm_nl_get_local_id(struct mptcp_sock *msk, struct sock_common *skc)
 	 * addr
 	 */
 	local_address((struct sock_common *)msk, &msk_local);
-	local_address((struct sock_common *)msk, &skc_local);
+	local_address((struct sock_common *)skc, &skc_local);
 	if (addresses_equal(&msk_local, &skc_local, false))
 		return 0;
 
+	if (address_zero(&skc_local))
+		return 0;
+
 	pernet = net_generic(sock_net((struct sock *)msk), pm_nl_pernet_id);
 
 	rcu_read_lock();