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Date:   Sat, 30 Oct 2021 12:09:16 +0800
From:   "Ziyang Xuan (William)" <>
To:     Jason Gunthorpe <>, Jakub Kicinski <>
CC:     <>, <>,
        <>, <>
Subject: Re: [PATCH net] net: vlan: fix a UAF in vlan_dev_real_dev()

> 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)

        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
> .

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