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

[Ziyang Xuan (William)]

> 
> Petr Machata <petrm@xxxxxxxxxx> writes:
> 
>> Ziyang Xuan (William) <william.xuanziyang@xxxxxxxxxx> writes:
>>
>>>>
>>>> Ziyang Xuan (William) <william.xuanziyang@xxxxxxxxxx> writes:
>>>>
>>>>> I need some time to test my some ideas. And anyone has good ideas, please
>>>>> do not be stingy.
>>>>
>>>> Jakub Kicinski <kuba@xxxxxxxxxx> writes:
>>>>
>>>>> 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.
>>>>
>>>> That makes sense to me. We always put real_dev in the destructor, so we
>>>> should always hold it in the constructor...
>>>
>>> Inject error before dev_hold(real_dev) in register_vlan_dev(), and execute
>>> the following testcase:
>>>
>>> ip link add dev dummy1 type dummy
>>> ip link add name dummy1.100 link dummy1 type vlan id 100 // failed for error injection
>>> ip link del dev dummy1
>>>
>>> Make the problem repro. The problem is solved using the following fix
>>> according to the Jakub's suggestion:
>>>
>>> diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
>>> index a3a0a5e994f5..abaa5d96ded2 100644
>>> --- a/net/8021q/vlan.c
>>> +++ b/net/8021q/vlan.c
>>> @@ -184,9 +184,6 @@ int register_vlan_dev(struct net_device *dev, struct netlink_ext_ack *extack)
>>>         if (err)
>>>                 goto out_unregister_netdev;
>>>
>>> -       /* Account for reference in struct vlan_dev_priv */
>>> -       dev_hold(real_dev);
>>> -
>>>         vlan_stacked_transfer_operstate(real_dev, dev, vlan);
>>>         linkwatch_fire_event(dev); /* _MUST_ call rfc2863_policy() */
>>>
>>> diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
>>> index ab6dee28536d..a54535cbcf4c 100644
>>> --- a/net/8021q/vlan_dev.c
>>> +++ b/net/8021q/vlan_dev.c
>>> @@ -615,6 +615,9 @@ static int vlan_dev_init(struct net_device *dev)
>>>         if (!vlan->vlan_pcpu_stats)
>>>                 return -ENOMEM;
>>>
>>> +       /* Get vlan's reference to real_dev */
>>> +       dev_hold(real_dev);
>>>
>>>
>>> If there is not any other idea and objection, I will send the fix patch later.
>>>
>>> Thank you!
>>
>> This fixes the issue in my repro, and does not seems to break anything.
>> We'll take it to full regression overnight, I'll report back tomorrow
>> about the result.
> 
> Sorry, was AFK yesterday. It does look good.
> .

Thank you for your efforts very much! I have sent the fix patch.