Re: [PATCH net] rtnetlink: allow to set iface down before enslaving it

[Phil Sutter <phil@nwl.cc>]

On Fri, Dec 29, 2023 at 11:08:35AM +0100, Nicolas Dichtel wrote:
> The below commit adds support for:
> > ip link set dummy0 down
> > ip link set dummy0 master bond0 up
> 
> but breaks the opposite:
> > ip link set dummy0 up
> > ip link set dummy0 master bond0 down
> 
> Let's add a workaround to have both commands working.
> 
> Cc: stable@vger.kernel.org
> Fixes: a4abfa627c38 ("net: rtnetlink: Enslave device before bringing it up")
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
> ---
>  net/core/rtnetlink.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index e8431c6c8490..dd79693c2d91 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -2905,6 +2905,14 @@ static int do_setlink(const struct sk_buff *skb,
>  		call_netdevice_notifiers(NETDEV_CHANGEADDR, dev);
>  	}
>  
> +	/* Backward compat: enable to set interface down before enslaving it */
> +	if (!(ifm->ifi_flags & IFF_UP) && ifm->ifi_change & IFF_UP) {
> +		err = dev_change_flags(dev, rtnl_dev_combine_flags(dev, ifm),
> +				       extack);
> +		if (err < 0)
> +			goto errout;
> +	}
> +
>  	if (tb[IFLA_MASTER]) {
>  		err = do_set_master(dev, nla_get_u32(tb[IFLA_MASTER]), extack);
>  		if (err)

Doesn't this merely revert to the old behaviour of setting the interface
up before enslaving if both IFF_UP and IFLA_MASTER are present? Did you
test this with a bond-type master?

Cheers, Phil