From: Haiyang Zhang haiyangz@microsoft.com

The loop in default_device_exit_net() won't be able to properly detect the head then stop, and will hit NULL pointer, when a driver, like hv_netvsc, automatically moves the slave device together with the master device.

To fix this, add a helper function to return the first migratable netdev correctly, no matter one or two devices were removed from this net's list in the last iteration.

Cc: stable@vger.kernel.org # 5.4+ Signed-off-by: Haiyang Zhang haiyangz@microsoft.com --- net/core/dev.c | 31 +++++++++++++++++++++---------- 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c index 621a639aeba1..d83f5f12cf70 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -12629,19 +12629,11 @@ static struct pernet_operations __net_initdata netdev_net_ops = { .exit = netdev_exit, };

-static void __net_exit default_device_exit_net(struct net *net) +static inline struct net_device *first_migratable_netdev(struct net *net) { - struct netdev_name_node *name_node, *tmp; struct net_device *dev, *aux; - /* - * Push all migratable network devices back to the - * initial network namespace - */ - ASSERT_RTNL(); - for_each_netdev_safe(net, dev, aux) { - int err; - char fb_name[IFNAMSIZ];

+ for_each_netdev_safe(net, dev, aux) { /* Ignore unmoveable devices (i.e. loopback) */ if (dev->netns_immutable) continue; @@ -12650,6 +12642,25 @@ static void __net_exit default_device_exit_net(struct net *net) if (dev->rtnl_link_ops && !dev->rtnl_link_ops->netns_refund) continue;

+ return dev; + } + + return NULL; +} + +static void __net_exit default_device_exit_net(struct net *net) +{ + struct netdev_name_node *name_node, *tmp; + struct net_device *dev; + /* + * Push all migratable network devices back to the + * initial network namespace + */ + ASSERT_RTNL(); + while ((dev = first_migratable_netdev(net)) != NULL) { + int err; + char fb_name[IFNAMSIZ]; + /* Push remaining network devices to init_net */ snprintf(fb_name, IFNAMSIZ, "dev%d", dev->ifindex); if (netdev_name_in_use(&init_net, fb_name))