Re: [PATCH net] ipvlan: update port flags only after ipvlan_set_port_mode() succeeds

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

Hi Wenbo,
On Wed, Nov 11, 2026 at 02:46:55PM +0800, Wenbo Sun wrote:
> In ipvlan_link_new(), the shared port->flags is updated before
> calling ipvlan_set_port_mode(). If ipvlan_set_port_mode() fails (e.g.
> switching to L3S mode without CONFIG_IPVLAN_L3S), the error unwinds via
> unlink_netdev, but the shared port->flags has already been modified and
> is never restored.

If ipvlan_set_port_mode() failed, the unregister_netdevice(dev) will be
called. Does port->flags still need to restore?

Thanks
Hangbin
> 
> As a result, subsequent operations on existing ipvlan interfaces on the
> same lower device operate with corrupted port flags (e.g., VEPA or
> PRIVATE flags inadvertently set or cleared).
> 
> Fix this by deferring the update of port->flags until after
> ipvlan_set_port_mode() returns successfully, matching the behaviour of
> ipvlan_nl_changelink().
> 
> This issue was identified with the assistance of an LLM-based code
> review tool, confirmed by reproducing the state corruption in a
> User-Mode Linux (UML) environment when ipvlan_set_port_mode() fails,
> and verified in UML that the shared port flags remain unchanged upon
> failure.
> 
> Fixes: a190d04db937 ("ipvlan: introduce 'private' attribute for all existing modes.")
> Signed-off-by: Wenbo Sun <sunwenbo@cmss.chinamobile.com>
> ---
>  drivers/net/ipvlan/ipvlan_main.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ipvlan/ipvlan_main.c b/drivers/net/ipvlan/ipvlan_main.c
> index f29864db662a..5732b167c5b3 100644
> --- a/drivers/net/ipvlan/ipvlan_main.c
> +++ b/drivers/net/ipvlan/ipvlan_main.c
> @@ -678,12 +678,6 @@ int ipvlan_link_new(struct net_device *dev, struct rtnl_newlink_params *params,
>  	if (err)
>  		goto remove_ida;
>  
> -	/* Flags are per port and latest update overrides. User has
> -	 * to be consistent in setting it just like the mode attribute.
> -	 */
> -	if (data && data[IFLA_IPVLAN_FLAGS])
> -		port->flags = nla_get_u16(data[IFLA_IPVLAN_FLAGS]);
> -
>  	if (data && data[IFLA_IPVLAN_MODE])
>  		mode = nla_get_u16(data[IFLA_IPVLAN_MODE]);
>  
> @@ -691,6 +685,12 @@ int ipvlan_link_new(struct net_device *dev, struct rtnl_newlink_params *params,
>  	if (err)
>  		goto unlink_netdev;
>  
> +	/* Flags are per port and latest update overrides. User has
> +	 * to be consistent in setting it just like the mode attribute.
> +	 */
> +	if (data && data[IFLA_IPVLAN_FLAGS])
> +		port->flags = nla_get_u16(data[IFLA_IPVLAN_FLAGS]);
> +
>  	mutex_lock(&port->pnodes_lock);
>  	list_add_tail_rcu(&ipvlan->pnode, &port->ipvlans);
>  	mutex_unlock(&port->pnodes_lock);
> -- 
> 2.33.0
> 
> 
>