Re: [PATCH v4] net: ravb: Fix possible UAF bug in ravb_remove

[Sergey Shtylyov <s.shtylyov@omp.ru>]

Hello!

On 7/27/23 11:21 AM, Paolo Abeni wrote:
[...]
>>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
>>> index 4d6b3b7d6abb..ce2da5101e51 100644
>>> --- a/drivers/net/ethernet/renesas/ravb_main.c
>>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
>>> @@ -2885,6 +2885,9 @@ static int ravb_remove(struct platform_device *pdev)
>>>  	struct ravb_private *priv = netdev_priv(ndev);
>>>  	const struct ravb_hw_info *info = priv->info;
>>>  
>>> +	netif_carrier_off(ndev);
>>> +	netif_tx_disable(ndev);
>>> +	cancel_work_sync(&priv->work);
>>
>> Still racy, the carrier can come back up after canceling the work.
> 
> I must admit I don't see how/when this driver sets the carrier on ?!?

   The phylib code does it for this MAC driver, see the call tree of
phy_link_change(), on e.g. https://elixir.bootlin.com/linux/v6.5-rc3/source/...

>> But whatever, this is a non-issue in the first place.
> 
> Do you mean the UaF can't happen? I think that is real. 

   Looks possible to me, at least now... and anyway, shouldn't we clean up
after ourselves if we call schedule_work()?However my current impression is
that cancel_work_sync() should be called from ravb_close(), after calling
phy_{stop|disconnect}()...

>> The fact that ravb_tx_timeout_work doesn't take any locks seems much
>> more suspicious.
> 
> Indeed! But that should be a different patch, right?

   Yes.

> Waiting a little more for feedback from renesas.

   Renesas historically hasn't shown much interest to reviewing the sh_eth/ravb
driver patches, so I took that task upon myself. I also happen to be a nominal
author of this driver... :-)

> /P

MBR, Sergey