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

[Yang Yingliang <yangyingliang@huawei.com>]

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
>   	devlink_params_unregister(devlink, nsim_devlink_params,
>   				  ARRAY_SIZE(nsim_devlink_params));
> -err_dl_unregister:
> +err_resource_unregister:
>   	devl_resources_unregister(devlink);
>   err_vfc_free:
>   	kfree(nsim_dev->vfconfigs);
> diff --git a/include/net/devlink.h b/include/net/devlink.h
> index 074a79b8933f..e0f13100fc6b 100644
> --- a/include/net/devlink.h
> +++ b/include/net/devlink.h
> @@ -1593,6 +1593,14 @@ void devlink_set_features(struct devlink *devlink, u64 features);
>   void devlink_register(struct devlink *devlink);
>   void devlink_unregister(struct devlink *devlink);
>   void devlink_free(struct devlink *devlink);
> +
> +void devl_register(struct devlink *devlink)
> +{
> +	devl_assert_locked(devlink);
> +	/* doesn't actually take the instance lock */
> +	devlink_register(devlink);
> +}
> +
>   void devlink_port_init(struct devlink *devlink,
>   		       struct devlink_port *devlink_port);
>   void devlink_port_fini(struct devlink_port *devlink_port);

How about the following changes, it's tested ok in my case:

diff --git a/drivers/net/netdevsim/dev.c b/drivers/net/netdevsim/dev.c
index a7880c7ce94c..0ec4590c26a0 100644
--- a/drivers/net/netdevsim/dev.c
+++ b/drivers/net/netdevsim/dev.c
@@ -1640,6 +1640,8 @@ int nsim_drv_probe(struct nsim_bus_dev *nsim_bus_dev)
      kfree(nsim_dev->vfconfigs);
  err_devlink_unlock:
      devl_unlock(devlink);
+    devl_put(devlink);
+    devl_wait_for_comp(devlink);
      devlink_free(devlink);
      dev_set_drvdata(&nsim_bus_dev->dev, NULL);
      return err;
diff --git a/include/net/devlink.h b/include/net/devlink.h
index ba6b8b094943..dc8ddf942c4d 100644
--- a/include/net/devlink.h
+++ b/include/net/devlink.h
@@ -1563,6 +1563,7 @@ static inline struct devlink *devlink_alloc(const 
struct devlink_ops *ops,
  void devlink_set_features(struct devlink *devlink, u64 features);
  void devlink_register(struct devlink *devlink);
  void devlink_unregister(struct devlink *devlink);
+void devl_wait_for_comp(struct devlink *devlink);
  void devlink_free(struct devlink *devlink);
  void devlink_port_init(struct devlink *devlink,
                 struct devlink_port *devlink_port);
@@ -1903,4 +1904,6 @@ devlink_compat_switch_id_get(struct net_device *dev,

  #endif

+void devl_put(struct devlink *devlink);
+
  #endif /* _NET_DEVLINK_H_ */
diff --git a/net/core/devlink.c b/net/core/devlink.c
index 89baa7c0938b..67c78cf37bac 100644
--- a/net/core/devlink.c
+++ b/net/core/devlink.c
@@ -248,6 +248,12 @@ void devlink_put(struct devlink *devlink)
          call_rcu(&devlink->rcu, __devlink_put_rcu);
  }

+void devl_put(struct devlink *devlink)
+{
+    devlink_put(devlink);
+}
+EXPORT_SYMBOL_GPL(devl_put);
+
  struct devlink *__must_check devlink_try_get(struct devlink *devlink)
  {
      if (refcount_inc_not_zero(&devlink->refcount))
@@ -9788,6 +9794,12 @@ void devlink_unregister(struct devlink *devlink)
  }
  EXPORT_SYMBOL_GPL(devlink_unregister);

+void devl_wait_for_comp(struct devlink *devlink)
+{
+    wait_for_completion(&devlink->comp);
+}
+EXPORT_SYMBOL_GPL(devl_wait_for_comp);
+
  /**
   *    devlink_free - Free devlink instance resources
   *
> .