sd-dhcp-client: do not call callback with SD_DHCP_CLIENT_EVENT_STOP if already stopped

When an interface enters the failed state, even if the DHCP client is
stopped, the acquired DHCP lease is not unreferenced, as the callback
dhcp4_handler() do nothing in that case. When the failed interface is
being reconfigured after that, the DHCP client is stopped again
(though it is already stopped), and SD_DHCP_CLIENT_EVENT_STOP event is
triggered and sd_dhcp_client_send_release() is called, and the
assertion in the function is triggered.

E.g.
===
systemd-networkd[98588]: wlp59s0: DHCPv4 address 192.168.86.250/24, gateway 192.168.86.1 acquired from 192.168.86.1
systemd-networkd[98588]: wlp59s0: Could not set DHCPv4 route: Nexthop has invalid gateway. Network is unreachable
systemd-networkd[98588]: wlp59s0: Failed
systemd-networkd[98588]: wlp59s0: State changed: configuring -> failed
systemd-networkd[98588]: wlp59s0: The interface entered the failed state frequently, refusing to reconfigure it automatically.
systemd-networkd[98588]: wlp59s0: DHCPv4 client: STOPPED
systemd-networkd[98588]: wlp59s0: DHCPv4 client: State changed: bound -> stopped
systemd-networkd[98588]: Got message type=method_call sender=:1.449 destination=org.freedesktop.network1 path=/org/freedesktop/network1 interface=org.freedesktop.network1.Manager member=ReconfigureLink ...
systemd-networkd[98588]: wlp59s0: State changed: failed -> initialized
systemd-networkd[98588]: wlp59s0: found matching network '/etc/systemd/network/50-wifi.network'.
systemd-networkd[98588]: wlp59s0: Configuring with /etc/systemd/network/50-wifi.network.
systemd-networkd[98588]: wlp59s0: DHCPv4 client: STOPPED
systemd-networkd[98588]: Assertion 'sd_dhcp_client_is_running(client)' failed at src/libsystemd-network/sd-dhcp-client.c:2197, function sd_dhcp_client_send_release(). Aborting.
===

1 files changed, 14 insertions, 8 deletions

diff --git a/src/libsystemd-network/sd-dhcp-client.c b/src/libsystemd-network/sd-dhcp-client.c
index 1eb8509f0f..8b8d0611a2 100644
--- a/src/libsystemd-network/sd-dhcp-client.c
+++ b/src/libsystemd-network/sd-dhcp-client.c
@@ -683,15 +683,21 @@ static int client_initialize(sd_dhcp_client *client) {
 
 static void client_stop(sd_dhcp_client *client, int error) {
         assert(client);
+        DHCP_CLIENT_DONT_DESTROY(client);
 
-        if (error < 0)
-                log_dhcp_client_errno(client, error, "STOPPED: %m");
-        else if (error == SD_DHCP_CLIENT_EVENT_STOP)
-                log_dhcp_client(client, "STOPPED");
-        else
-                log_dhcp_client(client, "STOPPED: Unknown event");
-
-        client_notify(client, error);
+        if (sd_dhcp_client_is_running(client)) {
+                if (error < 0)
+                        log_dhcp_client_errno(client, error, "STOPPED: %m");
+                else if (error == SD_DHCP_CLIENT_EVENT_STOP)
+                        log_dhcp_client(client, "STOPPED");
+                else
+                        log_dhcp_client(client, "STOPPED: Unknown event");
+
+                client_notify(client, error);
+        } else if (error < 0) {
+                log_dhcp_client_errno(client, error, "FAILED: %m");
+                client_notify(client, error);
+        }
 
         client_initialize(client);
 }