Shuang Li reported an QinQ issue by simply doing:
# ip link add dummy0 type dummy
# ip link add link dummy0 name dummy0.1 type vlan id 1
# ip link add link dummy0.1 name dummy0.1.2 type vlan id 2
# rmmod 8021q
unregister_netdevice: waiting for dummy0.1 to become free. Usage count = 1
When rmmods 8021q, all vlan devs are deleted from their real_dev's vlan grp
and added into list_kill by unregister_vlan_dev(). dummy0.1 is unregistered
before dummy0.1.2, as it's using for_each_netdev() in __rtnl_kill_links().
When unregisters dummy0.1, dummy0.1.2 is not unregistered in the event of
NETDEV_UNREGISTER, as it's been deleted from dummy0.1's vlan grp. However,
due to dummy0.1.2 still holding dummy0.1, dummy0.1 will keep waiting in
netdev_wait_allrefs(), while dummy0.1.2 will never get unregistered and
release dummy0.1, as it delays dev_put until calling dev->priv_destructor,
vlan_dev_free().
This issue was introduced by Commit 563bcbae3b ("net: vlan: fix a UAF in
vlan_dev_real_dev()"), and this patch is to fix it by moving dev_put() into
vlan_dev_uninit(), which is called after NETDEV_UNREGISTER event but before
netdev_wait_allrefs().
Fixes: 563bcbae3b ("net: vlan: fix a UAF in vlan_dev_real_dev()")
Reported-by: Shuang Li <shuali@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
d6ff94afd9