Re: [PATCH net v2] net: vlan: fix a UAF in vlan_dev_real_dev()

From: Ziyang Xuan (William)
Date: Thu Nov 18 2021 - 22:29:06 EST

> On Thu, 18 Nov 2021 09:46:24 +0800 Ziyang Xuan (William) wrote:
>>>> I think we should move the dev_hold() to ndo_init(), otherwise
>>>> it's hard to reason if destructor was invoked or not if
>>>> register_netdevice() errors out.
>>> Ziyang Xuan, do you intend to take care of this?
>>> .
>> I am reading the related processes according to the problem scenario.
>> And I will give a more clear sequence and root cause as soon as possible
>> by some necessary tests.
> Okay, I still don't see the fix.
> Petr would you mind submitting since you have a repro handy?
> .
The sequence for the problem maybe as following:

# create vlan device
vlan_newlink [assume real_dev refcnt == 2 just referenced by itself]
register_netdevice(vlan_dev) [success]
netdev_upper_dev_link [failed]
unregister_netdevice(vlan_dev) [failure process]
netdev_run_todo [vlan_dev]
vlan_dev_free(vlan_dev) [priv_destructor cb]
dev_put(real_dev) [real_dev refcnt == 1]

# delete real device
unregister_netdevice(real_dev) [real_dev refcnt == 1]
dev_put(real_dev) [real_dev refcnt == 0]
netdev_run_todo [real_dev]
netdev_wait_allrefs(real_dev) [real_dev refcnt == 0]
pr_emerg("unregister_netdevice: ...", ...)

I am thinking about how to fix the problem. priv_destructor() of the
net_device referenced not only by net_set_todo() but also failure process
in register_netdevice().

I need some time to test my some ideas. And anyone has good ideas, please
do not be stingy.

Thank you!