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SubjectRE: [PATCH v4] net: ravb: Fix possible UAF bug in ravb_remove
From
Hi,

On 12.10.2023 10:39, Yoshihiro Shimoda wrote:
> Hello Behme,
>
>> From: Behme Dirk (CM/ESO2), Sent: Tuesday, October 10, 2023 9:59 PM
>>
>> On 26.07.2023 05:19, Jakub Kicinski wrote:
>> ...
>>> The fact that ravb_tx_timeout_work doesn't take any locks seems much
>>> more suspicious.
>> Does anybody plan to look into this, too?
>
> I believe my fixed patch [1] resolved this issue too.


I'm not an expert of this driver nor the network stack, so sorry if I'm
totally wrong here ;) But somehow this answer confuses me. Let me explain:

What you did with [1] is to stop/cancel the workqueue in ravb_close().
That's fine. But that is at driver's close time.

What's about driver's normal runtime? What I understood is that
ravb_tx_timeout_work() might run totally asynchronously to the rest of
the driver. And therefore needs locking/protection/synchronization if it
uses resources of the driver which are used elsewhere in the driver, too.

I think this is exactly what is described with:

> ---
> Simplest fix I can think of is to take a reference on the netdev before
> scheduling the work, and then check if it's still registered in the work
> itself. Wrap the timeout work in rtnl_lock() to avoid any races there.
> ---

So, where is above done? Not at close time, but at normal run time of
the driver?

Best regards

Dirk

> Sergey suggested to add cancel_work_sync() into the ravb_close () [3].
> And I investigated calltrace, and then the ravb_close() is under rtnl_lock() [4]
> like below:
> -----------------------------------------------------------------------
> ravb_remove() calls unregister_netdev().
> -> unregister_netdev() calls rtnl_lock() and unregister_netdevice().
> --> unregiter_netdevice_queue()
> ---> unregiter_netdevice_many()
> ----> unregiter_netdevice_many_notify().
> -----> dev_close_many()
> ------> __dev_close_many()
> -------> ops->ndo_stop()
>
> ravb_close() calls phy_stop()
> -> phy_state_machine() with PHY_HALTED
> --> phy_link_down()
> ---> phy_link_change()
> ----> netif_carrier_off()
> -----------------------------------------------------------------------
>
> So, during cancel_work_sync() is waiting for canceling the workqueue in ravb_close(),
> it's under rtnl_lock() so that no additional locks are needed in ravb_tx_timeout_work().
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=3971442870713de527684398416970cf025b4f89
> [2] https://lore.kernel.org/netdev/20230727164820.48c9e685@kernel.org/
> [3] https://lore.kernel.org/netdev/607f4fe4-5a59-39dd-71c2-0cf769b48187@omp.ru/
> [4] https://lore.kernel.org/netdev/OSYPR01MB53341CFDBB49A3BA41A6752CD8F9A@OSYPR01MB5334.jpnprd01.prod.outlook.com/
>
> Best regards,
> Yoshihiro Shimoda
>
>> Best regards
>>
>> Dirk

--
======================================================================
Dirk Behme Robert Bosch Car Multimedia GmbH
CM/ESO2
Phone: +49 5121 49-3274 Dirk Behme
Fax: +49 711 811 5053274 PO Box 77 77 77
mailto:dirk.behme@de.bosch.com D-31132 Hildesheim - Germany

Bosch Group, Car Multimedia (CM)
Engineering SW Operating Systems 2 (ESO2)

Robert Bosch Car Multimedia GmbH - Ein Unternehmen der Bosch Gruppe
Sitz: Hildesheim
Registergericht: Amtsgericht Hildesheim HRB 201334
Aufsichtsratsvorsitzender: Dr. Dirk Hoheisel
Geschäftsführung: Dr. Steffen Berns;
Dr. Sven Ost, Jörg Pollak, Dr. Walter Schirm
======================================================================

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