strongSwan

I am using strongswan on a linux host that is using pppoe on a wan interface (interface name is pppoe-wan). I have also set

interfaces_use=pppoe-wan

in charon.conf. If the pppoe connection is dropped for one reason or another, charon correctly detects it and deactivates and deletes interface and its address:

2017-08-12T11:52:01.384013+02:00 swan pppd[14026]: Terminating on signal 15
2017-08-12T11:52:01.384155+02:00 swan pppd[14026]: Connect time 1238.5 minutes.
2017-08-12T11:52:01.384204+02:00 swan pppd[14026]: Sent 3975626 bytes, received 1742734 bytes.
2017-08-12T11:52:01.385009+02:00 swan charon: 01[KNL] interface pppoe-wan deactivated
2017-08-12T11:52:01.391010+02:00 swan charon: 08[KNL] 10.201.0.209 disappeared from pppoe-wan
2017-08-12T11:52:01.398327+02:00 swan pppd[14026]: Connection terminated.
2017-08-12T11:52:01.399265+02:00 swan charon: 13[KNL] interface pppoe-wan deleted
2017-08-12T11:52:01.445182+02:00 swan pppd[14026]: Sent PADT
2017-08-12T11:52:01.465524+02:00 swan pppd[14026]: Exit.

However later, when the connection is reestablished charon doesn't detect it and IKE communication is not reestablised:

2017-08-12T11:52:39.536333+02:00 swan pppd[3315]: Plugin rp-pppoe.so loaded.
2017-08-12T11:52:39.536550+02:00 swan pppd[3315]: RP-PPPoE plugin version 3.8p compiled against pppd 2.4.7
2017-08-12T11:52:39.653610+02:00 swan pppd[3315]: pppd 2.4.7 started by root, uid 0
2017-08-12T11:52:44.696467+02:00 swan pppd[3315]: PPP session is 3
2017-08-12T11:52:44.696552+02:00 swan pppd[3315]: Connected to 6c:3b:7e:62:a9:dc via interface eth0
2017-08-12T11:52:44.714735+02:00 swan kernel: [79025.853112] pppoe-wan: renamed from ppp0
2017-08-12T11:52:44.745002+02:00 swan pppd[3315]: Using interface pppoe-wan
2017-08-12T11:52:44.745224+02:00 swan pppd[3315]: Connect: pppoe-wan <--> eth0
2017-08-12T11:52:44.856800+02:00 swan pppd[3315]: CHAP authentication succeeded: Welcome.
2017-08-12T11:52:44.856867+02:00 swan pppd[3315]: CHAP authentication succeeded
2017-08-12T11:52:44.856913+02:00 swan pppd[3315]: peer from calling number 6C:3B:6B:62:A9:DC authorized
2017-08-12T11:52:44.884029+02:00 swan pppd[3315]: local  IP address 10.201.0.209
2017-08-12T11:52:44.884087+02:00 swan pppd[3315]: remote IP address 10.201.0.210

This happens because kernel_netlink first receives RTM_NEWLINK message for ppp0 interface and since it is not in a charon.interfaces_use list marks it as not usable. Later RTM_NEWLINK messages with a new/renamed name (pppoe-wan) are ignored as interface already exists in ifaces list (but is marked as not usable).

The solution is to set usable flag in each RTM_NEWLINK message processing:

--- a/src/libcharon/plugins/kernel_netlink/kernel_netlink_net.c
+++ b/src/libcharon/plugins/kernel_netlink/kernel_netlink_net.c
@@ -1192,6 +1192,8 @@
             }
             strncpy(entry->ifname, name, IFNAMSIZ);
             entry->ifname[IFNAMSIZ-1] = '\0';
+            if (!entry->usable)
+                entry->usable = charon->kernel->is_interface_usable(charon->kernel, name);
             if (event && entry->usable)
             {
                 if (!(entry->flags & IFF_UP) && (msg->ifi_flags & IFF_UP))

After applying the patch, charon correctly detects interface up event:

2017-08-12T22:23:24.662697+02:00 swan pppd[4022]: Plugin rp-pppoe.so loaded.
2017-08-12T22:23:24.662928+02:00 swan pppd[4022]: RP-PPPoE plugin version 3.8p compiled against pppd 2.4.7
2017-08-12T22:23:24.768112+02:00 swan pppd[4022]: pppd 2.4.7 started by root, uid 0
2017-08-12T22:23:29.796954+02:00 swan pppd[4022]: PPP session is 41
2017-08-12T22:23:29.797044+02:00 swan pppd[4022]: Connected to 6c:3b:7e:62:a9:dc via interface eth0
2017-08-12T22:23:29.819532+02:00 swan kernel: [  320.251407] pppoe-wan: renamed from ppp0
2017-08-12T22:23:29.850067+02:00 swan pppd[4022]: Using interface pppoe-wan
2017-08-12T22:23:29.850283+02:00 swan pppd[4022]: Connect: pppoe-wan <--> eth0
2017-08-12T22:23:29.958745+02:00 swan pppd[4022]: CHAP authentication succeeded: Welcome.
2017-08-12T22:23:29.958822+02:00 swan pppd[4022]: CHAP authentication succeeded
2017-08-12T22:23:29.958871+02:00 swan pppd[4022]: peer from calling number 6C:3B:6B:62:A9:DC authorized
2017-08-12T22:23:29.983180+02:00 swan pppd[4022]: local  IP address 10.201.0.209
2017-08-12T22:23:29.983641+02:00 swan pppd[4022]: remote IP address 10.201.0.210
2017-08-12T22:23:29.983699+02:00 swan charon: 13[KNL] 10.201.0.209 appeared on pppoe-wan
2017-08-12T22:23:29.984411+02:00 swan charon: 12[KNL] 10.201.0.209 disappeared from pppoe-wan
2017-08-12T22:23:29.984992+02:00 swan charon: 14[KNL] 10.201.0.209 appeared on pppoe-wan
2017-08-12T22:23:29.985683+02:00 swan charon: 04[KNL] interface pppoe-wan activated