cfg80211: preserve wdev ID across netns changes

When a wdev changes network namespace, its wdev ID will get
reassigned since NETDEV_REGISTER is called again, in the new
network namespace. Avoid that by checking if it was already
assigned before, and document why we do that.

Reported-and-tested-by: Arend Van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/net/wireless/core.c b/net/wireless/core.c
index b1a028d..b0d6761 100644 (file)
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -1159,7 +1159,15 @@ static int cfg80211_netdev_notifier_call(struct notifier_block *nb,
                INIT_LIST_HEAD(&wdev->mgmt_registrations);
                spin_lock_init(&wdev->mgmt_registrations_lock);
 
-               wdev->identifier = ++rdev->wdev_id;
+               /*
+                * We get here also when the interface changes network namespaces,
+                * as it's registered into the new one, but we don't want it to
+                * change ID in that case. Checking if the ID is already assigned
+                * works, because 0 isn't considered a valid ID and the memory is
+                * 0-initialized.
+                */
+               if (!wdev->identifier)
+                       wdev->identifier = ++rdev->wdev_id;
                list_add_rcu(&wdev->list, &rdev->wiphy.wdev_list);
                rdev->devlist_generation++;
                /* can only change netns with wiphy */