Subject: Re: [PATCH net] net: devlink: fix UAF in devlink_compat_running_version()

From: Leon Romanovsky <[email-masked]>
Date: Wed, 23 Nov 2022 11:33:14 +0200

On Wed, Nov 23, 2022 at 04:34:49PM +0800, Yang Yingliang wrote:
> 
> On 2022/11/23 15:41, Leon Romanovsky wrote:
> > On Wed, Nov 23, 2022 at 02:40:24PM +0800, Yang Yingliang wrote:
> > > On 2022/11/23 4:27, Jakub Kicinski wrote:
> > > > On Tue, 22 Nov 2022 21:04:29 +0200 Leon Romanovsky wrote:
> > > > > > > Please fix nsim instead of devlink.
> > > > > > I think if devlink is not registered, it can not be get and used, but there
> > > > > > is no API for driver to check this, can I introduce a new helper name
> > > > > > devlink_is_registered() for driver using.
> > > > > There is no need in such API as driver calls to devlink_register() and
> > > > > as such it knows when devlink is registered.
> > > > > 
> > > > > This UAF is nsim specific issue. Real devices have single .probe()
> > > > > routine with serialized registration flow. None of them will use
> > > > > devlink_is_registered() call.
> > > > Agreed, the fix is to move the register call back.
> > > > Something along the lines of the untested patch below?
> > > > Yang Yingliang would you be able to turn that into a real patch?
> > > > 
> > > > diff --git a/drivers/net/netdevsim/dev.c b/drivers/net/netdevsim/dev.c
> > > > index e14686594a71..26602d5fe0a2 100644
> > > > --- a/drivers/net/netdevsim/dev.c
> > > > +++ b/drivers/net/netdevsim/dev.c
> > > > @@ -1566,12 +1566,15 @@ int nsim_drv_probe(struct nsim_bus_dev *nsim_bus_dev)
> > > >    	err = devlink_params_register(devlink, nsim_devlink_params,
> > > >    				      ARRAY_SIZE(nsim_devlink_params));
> > > >    	if (err)
> > > > -		goto err_dl_unregister;
> > > > +		goto err_resource_unregister;
> > > >    	nsim_devlink_set_params_init_values(nsim_dev, devlink);
> > > > +	/* here, because params API still expect devlink to be unregistered */
> > > > +	devl_register(devlink);
> > > > +
> > > devlink_set_features() called at last in probe() also needs devlink is not
> > > registered.
> > > >    	err = nsim_dev_dummy_region_init(nsim_dev, devlink);
> > > >    	if (err)
> > > > -		goto err_params_unregister;
> > > > +		goto err_dl_unregister;
> > > >    	err = nsim_dev_traps_init(devlink);
> > > >    	if (err)
> > > > @@ -1610,7 +1613,6 @@ int nsim_drv_probe(struct nsim_bus_dev *nsim_bus_dev)
> > > >    	nsim_dev->esw_mode = DEVLINK_ESWITCH_MODE_LEGACY;
> > > >    	devlink_set_features(devlink, DEVLINK_F_RELOAD);
> > > >    	devl_unlock(devlink);
> > > > -	devlink_register(devlink);
> > > >    	return 0;
> > > >    err_hwstats_exit:
> > > > @@ -1629,10 +1631,11 @@ int nsim_drv_probe(struct nsim_bus_dev *nsim_bus_dev)
> > > >    	nsim_dev_traps_exit(devlink);
> > > >    err_dummy_region_exit:
> > > >    	nsim_dev_dummy_region_exit(nsim_dev);
> > > > -err_params_unregister:
> > > > +err_dl_unregister:
> > > > +	devl_unregister(devlink);
> > > It races with dev_ethtool():
> > > dev_ethtool
> > >    devlink_try_get()
> > >                                  nsim_drv_probe
> > >                                  devl_lock()
> > >      devl_lock()
> > >                                  devlink_unregister()
> > >                                    devlink_put()
> > >                                    wait_for_completion() <- the refcount is
> > > got in dev_ethtool, it causes ABBA deadlock
> > But all these races are nsim specific ones.
> > Can you please explain why devlink.[c|h] MUST be changed and nsim can't
> > be fixed?
> I used the fix code proposed by Jakub, but it didn't work correctly, so
> I tried to correct and improve it, and need some devlink helper.
> 
> Anyway, it is a nsim problem, if we want fix this without touch devlink,
> I think we can add a 'registered' field in struct nsim_dev, and it can be
> checked in nsim_get_devlink_port() like this:
> --- a/drivers/net/netdevsim/netdev.c
> +++ b/drivers/net/netdevsim/netdev.c
> @@ -242,6 +242,9 @@ static struct devlink_port *nsim_get_devlink_port(struct
> net_device *dev)
>  {
>         struct netdevsim *ns = netdev_priv(dev);
> 
> +       if (!ns->nsim_dev->devlink_registered)
> +               return NULL;

Something like that, but you need to make sure that this check is
protected by some sort of the locking.

> +
>         return &ns->nsim_dev_port->devlink_port;
>  }
> 
> Thanks,
> Yang
> > 
> > Thanks
> > .