Re: [PATCH net-next v2 1/3] net: ipvlan: fix potential UAF problem for phy_dev

On Fri, 18 Mar 2022 09:57:47 +0800 Ziyang Xuan wrote:

quoted

Add the reference operation to phy_dev of ipvlan to avoid
the potential UAF problem under the following known scenario:

Someone module puts the NETDEV_UNREGISTER event handler to a
work, and phy_dev is accessed in the work handler. But when
the work is excuted, phy_dev has been destroyed because upper
ipvlan did not get reference to phy_dev correctly.

That likes as the scenario occurred by
commit 563bcbae3ba2 ("net: vlan: fix a UAF in vlan_dev_real_dev()").

There is no equivalent of vlan_dev_real_dev() for ipvlan, AFAICT.
The definition of struct ipvl_dev is private to the driver. I don't 
see how a UAF can happen here.

You should either clearly explain how the bug could happen or clearly
state that there is no possibility of the bug for this driver, and the
patch is just future proofing.

If the latter is the case we should drop the Fixes tag and prevent this
patch from getting backported into stable.

It is to prevent ipvlan from occurring the similar problem in the future.
For now, there is not way to access phy_dev outside ipvlan module as vlan
real_dev using vlan_dev_real_dev(). I will make this clear.

I think it is necessary to protect lower netdevice using the feature of
netdevice refcnt. So I do it.

Thank you for your valuable opinions! I believe I can do more and more better
with your help.

quoted

Fixes: 2ad7bf363841 ("ipvlan: Initial check-in of the IPVLAN driver.")
Signed-off-by: Ziyang Xuan <redacted>

.