[PATCH 6.1.y] mptcp: pm: fullmesh: select the right ID later

["Matthieu Baerts (NGI0)" <matttbe@kernel.org>]

commit 09355f7abb9fbfc1a240be029837921ea417bf4f upstream.

When reacting upon the reception of an ADD_ADDR, the in-kernel PM first
looks for fullmesh endpoints. If there are some, it will pick them,
using their entry ID.

It should set the ID 0 when using the endpoint corresponding to the
initial subflow, it is a special case imposed by the MPTCP specs.

Note that msk->mpc_endpoint_id might not be set when receiving the first
ADD_ADDR from the server. So better to compare the addresses.

Fixes: 1a0d6136c5f0 ("mptcp: local addresses fullmesh")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240819-net-mptcp-pm-reusing-id-v1-12-38035d40de5b@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Conflicts in pm_netlink.c, because the new 'mpc_addr' variable is
  added where the 'local' one was, before commit b9d69db87fb7 ("mptcp:
  let the in-kernel PM use mixed IPv4 and IPv6 addresses"), that is not
  a candidate for the backports. This 'local' variable has been moved to
  the new place to reduce the scope, and help with possible future
  backports. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/pm_netlink.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 9e16ae1b23fc..a152a3474d2c 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -648,7 +648,7 @@ static unsigned int fill_local_addresses_vec(struct mptcp_sock *msk,
 {
 	struct sock *sk = (struct sock *)msk;
 	struct mptcp_pm_addr_entry *entry;
-	struct mptcp_addr_info local;
+	struct mptcp_addr_info mpc_addr;
 	struct pm_nl_pernet *pernet;
 	unsigned int subflows_max;
 	int i = 0;
@@ -656,6 +656,8 @@ static unsigned int fill_local_addresses_vec(struct mptcp_sock *msk,
 	pernet = pm_nl_get_pernet_from_msk(msk);
 	subflows_max = mptcp_pm_get_subflows_max(msk);
 
+	mptcp_local_address((struct sock_common *)msk, &mpc_addr);
+
 	rcu_read_lock();
 	list_for_each_entry_rcu(entry, &pernet->local_addr_list, list) {
 		if (!(entry->flags & MPTCP_PM_ADDR_FLAG_FULLMESH))
@@ -673,7 +675,13 @@ static unsigned int fill_local_addresses_vec(struct mptcp_sock *msk,
 
 		if (msk->pm.subflows < subflows_max) {
 			msk->pm.subflows++;
-			addrs[i++] = entry->addr;
+			addrs[i] = entry->addr;
+
+			/* Special case for ID0: set the correct ID */
+			if (mptcp_addresses_equal(&entry->addr, &mpc_addr, entry->addr.port))
+				addrs[i].id = 0;
+
+			i++;
 		}
 	}
 	rcu_read_unlock();
@@ -682,6 +690,8 @@ static unsigned int fill_local_addresses_vec(struct mptcp_sock *msk,
 	 * 'IPADDRANY' local address
 	 */
 	if (!i) {
+		struct mptcp_addr_info local;
+
 		memset(&local, 0, sizeof(local));
 		local.family = msk->pm.remote.family;
 
-- 
2.45.2