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

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Message-Id: <20231229100835.3996906-1-nicolas.dichtel@6wind.com>
Date: Fri, 29 Dec 2023 11:08:35 +0100
From: Nicolas Dichtel <nicolas.dichtel@...nd.com>
To: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Phil Sutter <phil@....cc>,
	David Ahern <dsahern@...nel.org>
Cc: netdev@...r.kernel.org,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	stable@...r.kernel.org
Subject: [PATCH net] rtnetlink: allow to set iface down before enslaving it

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)
-- 
2.39.2