Comment # 7 on bug 1081430 from Bruno Friedmann

New test done with nmcli
Edit the connection with the plasma5 applet, save it

Try to make it up with nmcli give always a coredump

Feb 24 11:53:51 dbus-daemon[1224]: [system] Rejected send message, 1 matched
rules; type="method_call", sender=":1.6" (uid=0 pid=1289
comm="/usr/sbin/NetworkManager --no-daemon ")
interface="org.freedesktop.NetworkManager.SecretAgent" member="GetSecrets"
error name="(unset)" requested_reply="0" destination=":1.21" (uid=1502 pid=2329
comm="kded5 [kdeinit5]                                  ")
Feb 24 11:54:28 dbus-daemon[1224]: [system] Rejected send message, 1 matched
rules; type="method_call", sender=":1.6" (uid=0 pid=1289
comm="/usr/sbin/NetworkManager --no-daemon ")
interface="org.freedesktop.NetworkManager.SecretAgent" member="GetSecrets"
error name="(unset)" requested_reply="0" destination=":1.21" (uid=1502 pid=2329
comm="kded5 [kdeinit5]                                  ")
Feb 24 11:54:43 systemd[1]: Started PC/SC Smart Card Daemon.
Feb 24 11:56:24 NetworkManager[1289]: <info>  [1519469784.4748]
settings-connection[0x565523120440,3e125064-5541-4e6f-8904-427fe62a96b7]:
write: successfully updated (keyfile: update
/etc/NetworkManager/system-connections/vpn-botta
(3e125064-5541-4e6f-8904-427fe62a96b7,"vpn-botta"))
Feb 24 11:56:24 NetworkManager[1289]: <info>  [1519469784.4752] audit:
op="connection-update" uuid="3e125064-5541-4e6f-8904-427fe62a96b7"
name="vpn-botta"
args="vpn.data,ipv4.may-fail,ipv4.never-default,ipv6.ip6-privacy" pid=3410
uid=1502 result="success"
Feb 24 11:56:24 dbus-daemon[1224]: [system] Rejected send message, 1 matched
rules; type="method_call", sender=":1.6" (uid=0 pid=1289
comm="/usr/sbin/NetworkManager --no-daemon ")
interface="org.freedesktop.NetworkManager.SecretAgent" member="SaveSecrets"
error name="(unset)" requested_reply="0" destination=":1.21" (uid=1502 pid=2329
comm="kded5 [kdeinit5]                                  ")
Feb 24 11:58:08 NetworkManager[1289]: <info>  [1519469888.1213] audit:
op="connection-activate" uuid="3e125064-5541-4e6f-8904-427fe62a96b7"
name="vpn-botta" pid=3577 uid=1502 result="success"
Feb 24 11:58:08 NetworkManager[1289]: <info>  [1519469888.1269]
vpn-connection[0x565523318110,3e125064-5541-4e6f-8904-427fe62a96b7,"vpn-botta",0]:
Started the VPN service, PID 3583
Feb 24 11:58:08 NetworkManager[1289]: <info>  [1519469888.1345]
vpn-connection[0x565523318110,3e125064-5541-4e6f-8904-427fe62a96b7,"vpn-botta",0]:
Saw the service appear; activating connection
Feb 24 11:58:08 kernel: tun: Universal TUN/TAP device driver, 1.6
Feb 24 11:58:08 NetworkManager[1289]: **
Feb 24 11:58:08 NetworkManager[1289]:
NetworkManager:ERROR:src/settings/nm-agent-manager.c:542:<unknown-fcn>: code
should not be reached
Feb 24 11:58:08 systemd[1]: Created slice system-systemd\x2dcoredump.slice.
Feb 24 11:58:08 systemd[1]: Started Process Core Dump (PID 3589/UID 0).
Feb 24 11:58:08 systemd-coredump[3590]: Removed old coredump
core.NetworkManager.0.ddddf9223bd041f9a2b2d4bbc4906911.4751.1519403535000000.lz4.
Feb 24 11:58:08 systemd[1]: NetworkManager.service: Main process exited,
code=dumped, status=6/ABRT
Feb 24 11:58:08 systemd[1]: NetworkManager.service: Unit entered failed state.
Feb 24 11:58:08 systemd[1]: NetworkManager.service: Failed with result
'core-dump'.
Feb 24 11:58:08 systemd-coredump[3590]: Process 1289 (NetworkManager) of user 0
dumped core.

Could it be possible that the first two lines are related too ?

Also by default dbus is complaining about missing destination in 

/etc/dbus-1/system.d/org.freedesktop.NetworkManager.conf


12 <allow send_destination="org.freedesktop.NetworkManager"
13        send_interface="org.freedesktop.NetworkManager.SecretAgent"/>

30 <allow send_destination="org.freedesktop.NetworkManager"
31        send_interface="org.freedesktop.NetworkManager.VPN.Plugin"/>

So I've rewrite the two lines to containg a send_destination