Subject: Re: [PATCH net] net: fix stack overflow when LRO is disabled for virtual interfaces

From: Simon Horman <[email-masked]>
Date: Mon, 15 May 2023 15:11:08 +0200

On Mon, May 15, 2023 at 05:37:40AM +0000, Taehee Yoo wrote:
> When the virtual interface's feature is updated, it synchronizes the
> updated feature for its own lower interface.
> This propagation logic should be worked as the iteration, not recursively.
> But it works recursively due to the netdev notification unexpectedly.
> This problem occurs when it disables LRO only for the team and bonding
> interface type.
> 
>        team0
>          |
>   +------+------+-----+-----+
>   |      |      |     |     |
> team1  team2  team3  ...  team200
> 
> If team0's LRO feature is updated, it generates the NETDEV_FEAT_CHANGE
> event to its own lower interfaces(team1 ~ team200).
> It is worked by netdev_sync_lower_features().
> So, the NETDEV_FEAT_CHANGE notification logic of each lower interface
> work iteratively.
> But generated NETDEV_FEAT_CHANGE event is also sent to the upper
> interface too.
> upper interface(team0) generates the NETDEV_FEAT_CHANGE event for its own
> lower interfaces again.
> lower and upper interfaces receive this event and generate this
> event again and again.
> So, the stack overflow occurs.
> 
> But it is not the infinite loop issue.
> Because the netdev_sync_lower_features() updates features before
> generating the NETDEV_FEAT_CHANGE event.
> Already synchronized lower interfaces skip notification logic.
> So, it is just the problem that iteration logic is changed to the
> recursive unexpectedly due to the notification mechanism.
> 
> Reproducer:
> 
> ip link add team0 type team
> ethtool -K team0 lro on
> for i in {1..200}
> do
>         ip link add team$i master team0 type team
>         ethtool -K team$i lro on
> done
> 
> ethtool -K team0 lro off
> 
> In order to fix it, the priv_notifier_ctx net_device member is introduced.
> This variable can be used by each interface in its own way in the
> notification context. The bonding and team interface is going to use it
> to avoid duplicated NETDEV_FEAT_CHANGE event handling.
> 
> Reported-by: [email-masked]
> Fixes: fd867d51f889 ("net/core: generic support for disabling netdev features down stack")
> Signed-off-by: Taehee Yoo <[email-masked]>

...

> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 08fbd4622ccf..ebd49a54f0d5 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -2393,6 +2393,7 @@ struct net_device {
>  	unsigned		threaded:1;
>  
>  	struct list_head	net_notifier_list;
> +	u32			priv_notifier_ctx;

Hi Taehee,

Please add this new field to the kdoc for struct net_device.

>  
>  #if IS_ENABLED(CONFIG_MACSEC)
>  	/* MACsec management functions */

...

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