network: fix crash when Wi-Fi or eth interface gets removed from the …

…system

When a network interface is disconnected from the system (e.g.,
physically removed if it's a USB adapter), probert asynchronously calls
the del_link() method.

Upon receiving this notification, Subiquity server wants to send an
update to the Subiquity clients. The update contains information about
the interface that disappeared - which is obtained through a call to
netdev_info.

Unfortunately, for Wi-Fi and Ethernet interfaces, netdev_info
dereferences the NetworkDev.info variable. Interfaces that no longer
exist on the system (and also interfaces that do not yet exist), have
their "info" variable set to None - so an exception is raised when
dereferencing it.

Wi-Fi interface:

    File "subiquitycore/models/network.py", line 227, in netdev_info
      scan_state=self.info.wlan['scan_state'],
  AttributeError: 'NoneType' object has no attribute 'wlan'

Ethernet interface:

    File "subiquitycore/models/network.py", line 201, in netdev_info
      is_connected = bool(self.info.is_connected)
  AttributeError: 'NoneType' object has no attribute 'is_connected'

Fixed by making sure netdev_info does not raise if the dev.info variable
is None. This is a valid use-case.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquitycore/models/network.py

@@ -205,7 +205,12 @@ def __init__(self, model, name, typ):
 
     def netdev_info(self) -> NetDevInfo:
         if self.type == "eth":
-            is_connected = bool(self.info.is_connected)
+            if self.info is not None:
+                is_connected = bool(self.info.is_connected)
+            else:
+                # If the device has just disappeared, let's pretend it's not
+                # connected.
+                is_connected = False
         else:
             is_connected = True
         bond_master = None
@@ -230,10 +235,17 @@ def netdev_info(self) -> NetDevInfo:
         wlan: Optional[WLANStatus] = None
         if self.type == "wlan":
             ssid, psk = self.configured_ssid
+            # If the device has just disappeared, let's pretend it's not
+            # scanning and has no visible SSID.
+            scan_state = None
+            visible_ssids: List[str] = []
+            if self.info is not None:
+                scan_state = self.info.wlan["scan_state"]
+                visible_ssids = self.info.wlan["visible_ssids"]
             wlan = WLANStatus(
                 config=WLANConfig(ssid=ssid, psk=psk),
-                scan_state=self.info.wlan["scan_state"],
-                visible_ssids=self.info.wlan["visible_ssids"],
+                scan_state=scan_state,
+                visible_ssids=visible_ssids,
             )
 
         dhcp_addresses = self.dhcp_addresses()

subiquitycore/models/tests/test_network.py

@@ -13,6 +13,8 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+from unittest.mock import Mock
+
 from subiquitycore.models.network import NetworkDev
 from subiquitycore.tests import SubiTestCase
 
@@ -39,3 +41,26 @@ def test_remove_v6(self):
         self.nd.remove_routes(6)
         expected = self.ipv4s
         self.assertEqual(expected, self.nd.config["routes"])
+
+
+class TestNetworkDev(SubiTestCase):
+    def test_netdev_info_eth_inexistent(self):
+        # LP: #2012659 - just after physically removing an Ethernet interface
+        # from the system, Subiquity tries to collect information via
+        # netdev_info. The code would try to dereference dev.info - but it was
+        # reset to None when the interface got removed.
+        # In other private reports, the same issue would occur with Wi-Fi
+        # interfaces.
+        model = Mock(get_all_netdevs=Mock(return_value=[]))
+        nd = NetworkDev(model, "testdev0", "eth")
+        info = nd.netdev_info()
+        self.assertFalse(info.is_connected)
+
+    def test_netdev_info_wlan_inexistent(self):
+        # Just like test_netdev_info_eth_inexistent but with Wi-Fi interfaces
+        # which suffer the same issue.
+        model = Mock(get_all_netdevs=Mock(return_value=[]))
+        nd = NetworkDev(model, "testdev0", "wlan")
+        info = nd.netdev_info()
+        self.assertIsNone(info.wlan.scan_state)
+        self.assertEqual(info.wlan.visible_ssids, [])