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

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Message-ID: <ZZSIGBWSaK2-sqoI@orbyte.nwl.cc>
Date: Tue, 2 Jan 2024 23:03:04 +0100
From: Phil Sutter <phil@....cc>
To: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH net] rtnetlink: allow to set iface down before enslaving
 it

On Tue, Jan 02, 2024 at 01:14:21PM +0100, Nicolas Dichtel wrote:
> Le 01/01/2024 à 23:10, Phil Sutter a écrit :
> > 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@...r.kernel.org
> >> Fixes: a4abfa627c38 ("net: rtnetlink: Enslave device before bringing it up")
> >> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.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?
> Yes, both command sequences (cf commit log) work after the patch.
> dev_change_flags() is called before do_set_master() only if the user asks to
> remove the flag IFF_UP.

Ah, indeed! I should have looked at rtnl_dev_combine_flags() before
commenting. When submitting v2, feel free to add my:

Acked-by: Phil Sutter <phil@....cc>

Thanks, Phil