2 files changed, 49 insertions, 1 deletions

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 1313456a0994..9d22f08896c6 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -74,6 +74,7 @@ struct net {
         struct hlist_head       *dev_index_head;
         unsigned int            dev_base_seq;   /* protected by rtnl_mutex */
         int                     ifindex;
+        unsigned int            dev_unreg_count;
 
         /* core fib_rules */
         struct list_head        rules_ops;
diff --git a/net/core/dev.c b/net/core/dev.c
index 5c713f2239cc..65f829cfd928 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5247,10 +5247,12 @@ static int dev_new_index(struct net *net)
 
 /* Delayed registration/unregisteration */
 static LIST_HEAD(net_todo_list);
+static DECLARE_WAIT_QUEUE_HEAD(netdev_unregistering_wq);
 
 static void net_set_todo(struct net_device *dev)
 {
         list_add_tail(&dev->todo_list, &net_todo_list);
+        dev_net(dev)->dev_unreg_count++;
 }
 
 static void rollback_registered_many(struct list_head *head)
@@ -5918,6 +5920,12 @@ void netdev_run_todo(void)
                 if (dev->destructor)
                         dev->destructor(dev);
 
+                /* Report a network device has been unregistered */
+                rtnl_lock();
+                dev_net(dev)->dev_unreg_count--;
+                __rtnl_unlock();
+                wake_up(&netdev_unregistering_wq);
+
                 /* Free network device */
                 kobject_put(&dev->dev.kobj);
         }
@@ -6603,6 +6611,34 @@ static void __net_exit default_device_exit(struct net *net)
         rtnl_unlock();
 }
 
+static void __net_exit rtnl_lock_unregistering(struct list_head *net_list)
+{
+        /* Return with the rtnl_lock held when there are no network
+         * devices unregistering in any network namespace in net_list.
+         */
+        struct net *net;
+        bool unregistering;
+        DEFINE_WAIT(wait);
+
+        for (;;) {
+                prepare_to_wait(&netdev_unregistering_wq, &wait,
+                                TASK_UNINTERRUPTIBLE);
+                unregistering = false;
+                rtnl_lock();
+                list_for_each_entry(net, net_list, exit_list) {
+                        if (net->dev_unreg_count > 0) {
+                                unregistering = true;
+                                break;
+                        }
+                }
+                if (!unregistering)
+                        break;
+                __rtnl_unlock();
+                schedule();
+        }
+        finish_wait(&netdev_unregistering_wq, &wait);
+}
+
 static void __net_exit default_device_exit_batch(struct list_head *net_list)
 {
         /* At exit all network devices most be removed from a network
@@ -6614,7 +6650,18 @@ static void __net_exit default_device_exit_batch(struct list_head *net_list)
         struct net *net;
         LIST_HEAD(dev_kill_list);
 
-        rtnl_lock();
+        /* To prevent network device cleanup code from dereferencing
+         * loopback devices or network devices that have been freed
+         * wait here for all pending unregistrations to complete,
+         * before unregistring the loopback device and allowing the
+         * network namespace be freed.
+         *
+         * The netdev todo list containing all network devices
+         * unregistrations that happen in default_device_exit_batch
+         * will run in the rtnl_unlock() at the end of
+         * default_device_exit_batch.
+         */
+        rtnl_lock_unregistering(net_list);
         list_for_each_entry(net, net_list, exit_list) {
                 for_each_netdev_reverse(net, dev) {
                         if (dev->rtnl_link_ops)