netdev - RE: [PATCH v4] net: ravb: Fix possible UAF bug in ravb

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Date: Fri, 13 Oct 2023 08:04:45 +0200
From: "Behme Dirk (CM/ESO2)" <dirk.behme@...bosch.com>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
CC: "s.shtylyov@....ru" <s.shtylyov@....ru>, "lee@...nel.org"
	<lee@...nel.org>, "linyunsheng@...wei.com" <linyunsheng@...wei.com>,
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	<alex000young@...il.com>, Zheng Wang <zyytlz.wz@....com>, Jakub Kicinski
	<kuba@...nel.org>
Subject: RE: [PATCH v4] net: ravb: Fix possible UAF bug in ravb_remove

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
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              Engineering SW Operating Systems 2 (ESO2)

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