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

[Yoshihiro Shimoda]

Hello Sergey!

> From: Sergey Shtylyov, Sent: Friday, July 28, 2023 3:49 AM
> 
> 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}()...

I also think so.

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()

The patch will be the following:
---
 drivers/net/ethernet/renesas/ravb_main.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index 7df9f9f8e134..e452d90de7c2 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -2167,6 +2167,8 @@ static int ravb_close(struct net_device *ndev)
 			of_phy_deregister_fixed_link(np);
 	}
 
+	cancel_work_sync(&priv->work);
+
 	if (info->multi_irqs) {
 		free_irq(priv->tx_irqs[RAVB_NC], ndev);
 		free_irq(priv->rx_irqs[RAVB_NC], ndev);
---

If this patch is acceptable, I'll submit it. But, what do you think?

Best regards,
Yoshihiro Shimoda

> >> 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