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

[Ziyang Xuan (William)]

> On Fri, Oct 29, 2021 at 06:46:10AM -0700, Jakub Kicinski wrote:
>> On Fri, 29 Oct 2021 09:13:24 -0300 Jason Gunthorpe wrote:
>>> Jakub's path would be to test vlan_dev->reg_state != NETREG_REGISTERED
>>> in the work queue, but that feels pretty hacky to me as the main point
>>> of the UNREGISTERING state is to keep the object alive enough that
>>> those with outstanding gets can compelte their work and release the
>>> get. Leaving a wrecked object in UNREGISTERING is a bad design.
>>
>> That or we should investigate if we could hold the ref for real_dev all
>> the way until vlan_dev_free().
> 

Synchronize test results with the following modification:

@@ -123,9 +123,6 @@ void unregister_vlan_dev(struct net_device *dev, struct list_head *head)
        }

        vlan_vid_del(real_dev, vlan->vlan_proto, vlan_id);
-
-       /* Get rid of the vlan's reference to real_dev */
-       dev_put(real_dev);
 }

@@ -843,6 +843,9 @@ static void vlan_dev_free(struct net_device *dev)

        free_percpu(vlan->vlan_pcpu_stats);
        vlan->vlan_pcpu_stats = NULL;
+
+       /* Get rid of the vlan's reference to real_dev */
+       dev_put(vlan->real_dev);
 }

It works on the UAF problem. And I have taken kmemleak tests for vlan_dev and real_dev,
no kmemleak problem and new UAF problem.

So take this modification for this problem?

> The latter is certainly better if it works out, no circular deps, etc.
> 
> Thanks,
> Jason
> .
>