Re: [PATCH net] net: hsr: clean up synced addresses and allmulti in hsr_del_port()

[Hangbin Liu <hangbin.liu@linux.dev>]

On Wed, Nov 11, 2026 at 02:01:43PM +0800, Wenbo Sun wrote:
> hsr_set_rx_mode() syncs unicast and multicast addresses to slave A and
> slave B devices via dev_uc_sync_multiple() and dev_mc_sync_multiple(),
> and hsr_change_rx_flags() propagates IFF_ALLMULTI via
> dev_set_allmulti().
> 
> However, when an HSR device is deleted via hsr_dellink(),
> hsr_del_ports() removes all ports from hsr->ports before
> unregister_netdevice_queue() invokes hsr_dev_close(). Similarly, when a
> slave device is unregistered while the HSR master is UP,
> hsr_netdev_notify() calls hsr_del_port() directly. Because
> hsr_del_port() does not unsync unicast/multicast addresses or restore
> the allmulti count, the slave devices permanently retain synced hardware
> addresses and a leaked allmulti reference count after port deletion.
> 
> Fix this by calling dev_uc_unsync() and dev_mc_unsync(), and
> decrementing allmulti via dev_set_allmulti(port->dev, -1) if
> IFF_ALLMULTI is set on the master device, when detaching slave A or
> slave B in hsr_del_port().
> 
> This issue was identified with the assistance of an LLM-based code
> review tool, confirmed by reproducing the leaked allmulti reference
> count and synced multicast address in a User-Mode Linux (UML)
> environment, and verified in UML that both states are properly cleaned
> up upon HSR port deletion.
> 
> Fixes: 36b20fcdd966 ("net: hsr: Add support for MC filtering at the slave device")
> Signed-off-by: Wenbo Sun <sunwenbo@cmss.chinamobile.com>
> ---
>  net/hsr/hsr_slave.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/net/hsr/hsr_slave.c b/net/hsr/hsr_slave.c
> index a546f70f9cc8..bab0c27dd06a 100644
> --- a/net/hsr/hsr_slave.c
> +++ b/net/hsr/hsr_slave.c
> @@ -245,8 +245,14 @@ void hsr_del_port(struct hsr_port *port)
>  		netdev_rx_handler_unregister(port->dev);
>  		if (!port->hsr->fwd_offloaded || port->type == HSR_PT_INTERLINK)
>  			dev_set_promiscuity(port->dev, -1);
> -		if (port->type == HSR_PT_SLAVE_A || port->type == HSR_PT_SLAVE_B)
> +		if (port->type == HSR_PT_SLAVE_A ||
> +		    port->type == HSR_PT_SLAVE_B) {
>  			vlan_vids_del_by_dev(port->dev, master->dev);
> +			dev_uc_unsync(port->dev, master->dev);
> +			dev_mc_unsync(port->dev, master->dev);
> +			if (master->dev->flags & IFF_ALLMULTI)
> +				dev_set_allmulti(port->dev, -1);
> +		}
>  		netdev_upper_dev_unlink(port->dev, master->dev);
>  		if (hsr->prot_version == PRP_V1 &&
>  		    port->type == HSR_PT_SLAVE_B) {
> -- 
> 2.33.0
> 
> 
> 

Reviewed-by: Hangbin Liu <liuhangbin@kylinos.cn>