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

[Yoshihiro Shimoda]

Hi,

> From: Behme Dirk (CM/ESO2), Sent: Friday, October 13, 2023 3:05 PM
>
> 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?

Thank you very much for your detailed explanation. I understood it.
ravb_tx_timeout_work() still has races between ethtool ops for instance.
So, I'll make a patch for it by early next week. However, IIUC, using
rtnl_lock() in ravb_tx_timeout_work() is possible to cause deadlock from
cancel_work_sync() in ravb_close(). So, I'll use rtnl_trylock() instead.

Best regards,
Yoshihiro Shimoda

> 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%25
> 2Fnetdev%2Fnet.git%2Fcommit%2F%3Fid%3D3971442870713de527684398416970cf025b4f89&data=05%7C01%7Cyoshihiro.shimoda.uh%4
> 0renesas.com%7C466e046b20b548b264f808dbcbb255f6%7C53d82571da1947e49cb4625a166a4a2a%7C0%7C0%7C638327739033548199%7CUn
> known%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=HkA8f5a
> gawjXMvAGkaE6tELaSpjpbIn7M3mU5xbDTD0%3D&reserved=0
> > [2]
> https://lore.kernel.org/netdev/20230727164820.48c9e685
> %40kernel.org%2F&data=05%7C01%7Cyoshihiro.shimoda.uh%40renesas.com%7C466e046b20b548b264f808dbcbb255f6%7C53d82571da19
> 47e49cb4625a166a4a2a%7C0%7C0%7C638327739033548199%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTi
> I6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=cGvnA8WqxM%2FUDa%2FNS2OBztr1IWgjCX4IzBYXe1LGkZU%3D&reserved=0
> > [3]
> https://lore.kernel.org/netdev/607f4fe4-5a59-39dd-71c2
> -0cf769b48187%40omp.ru%2F&data=05%7C01%7Cyoshihiro.shimoda.uh%40renesas.com%7C466e046b20b548b264f808dbcbb255f6%7C53d
> 82571da1947e49cb4625a166a4a2a%7C0%7C0%7C638327739033548199%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luM
> zIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=OWwBKy%2Fdckgo3clPPfn2hxE4H6ToyqdcbhPhGoqoo30%3D&reserved=0
> > [4]
> https://lore.kernel.org/netdev/OSYPR01MB53341CFDBB49A3
> BA41A6752CD8F9A%40OSYPR01MB5334.jpnprd01.prod.outlook.com%2F&data=05%7C01%7Cyoshihiro.shimoda.uh%40renesas.com%7C466
> e046b20b548b264f808dbcbb255f6%7C53d82571da1947e49cb4625a166a4a2a%7C0%7C0%7C638327739033548199%7CUnknown%7CTWFpbGZsb3
> d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=Jfypf10jiUfTqWUAukjnPzIQp
> urx7m0ETF5N2Toq8wE%3D&reserved=0
> >
> > 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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>
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