usersession/agent: only close session bus if non-nil

On Ubuntu 16.04, ssh sessions may not have a D-Bus session bus, resulting in the `bus` field of the session agent being nil. If this is the case, calling `s.bus.Close()` results in a nil pointer exception. This commit adds a check of `s.bus` (like those found elsewhere in session_agent.go) before calling `s.bus.Close()` during a session shutdown. Discovered-by: Andrew Phelps <andrew.phelps@canonical.com> Signed-off-by: Oliver Calder <oliver.calder@canonical.com> 

1 files changed, 4 insertions, 1 deletions

diff --git a/usersession/agent/session_agent.go b/usersession/agent/session_agent.go
index 34ad645ac0..b3d064cd1e 100644
--- a/usersession/agent/session_agent.go
+++ b/usersession/agent/session_agent.go
@@ -276,7 +276,10 @@ func (s *SessionAgent) shutdownServerOnKill() error {
	// Historically We do something similar in the main daemon
	// logic as well.
	s.listener.Close()
-	s.bus.Close()
+	// Note that session bus may be nil, see the comment in tryConnectSessionBus.
+	if s.bus != nil {
+	s.bus.Close()
+	}
	ctx, cancel := context.WithTimeout(context.Background(), shutdownTimeout)
	defer cancel()
	return s.serve.Shutdown(ctx)