[PATCH 5.10 v2 1/3] bonding: restore IFF_MASTER/SLAVE flags on bond enslave ether type change

From: Nikolay Aleksandrov <razor@blackwall.org>

[ Upstream commit 9ec7eb60dcbcb6c41076defbc5df7bbd95ceaba5 ]

Add bond_ether_setup helper which is used to fix ether_setup() calls in the
bonding driver. It takes care of both IFF_MASTER and IFF_SLAVE flags, the
former is always restored and the latter only if it was set.
If the bond enslaves non-ARPHRD_ETHER device (changes its type), then
releases it and enslaves ARPHRD_ETHER device (changes back) then we
use ether_setup() to restore the bond device type but it also resets its
flags and removes IFF_MASTER and IFF_SLAVE[1]. Use the bond_ether_setup
helper to restore both after such transition.

[1] reproduce (nlmon is non-ARPHRD_ETHER):
 $ ip l add nlmon0 type nlmon
 $ ip l add bond2 type bond mode active-backup
 $ ip l set nlmon0 master bond2
 $ ip l set nlmon0 nomaster
 $ ip l add bond1 type bond
 (we use bond1 as ARPHRD_ETHER device to restore bond2's mode)
 $ ip l set bond1 master bond2
 $ ip l sh dev bond2
 37: bond2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether be:d7:c5:40:5b:cc brd ff:ff:ff:ff:ff:ff promiscuity 0 minmtu 68 maxmtu 1500
 (notice bond2's IFF_MASTER is missing)

Fixes: e36b9d16c6a6 ("bonding: clean muticast addresses when device changes type")
Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Alexey Panov <redacted>
---
 drivers/net/bonding/bond_main.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 08bc930afc4c..127242101c8e 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c

@@ -1691,6 +1691,19 @@ void bond_lower_state_changed(struct slave *slave)
 	netdev_lower_state_changed(slave->dev, &info);
 }
 
+/* The bonding driver uses ether_setup() to convert a master bond device
+ * to ARPHRD_ETHER, that resets the target netdevice's flags so we always
+ * have to restore the IFF_MASTER flag, and only restore IFF_SLAVE if it was set
+ */
+static void bond_ether_setup(struct net_device *bond_dev)
+{
+	unsigned int slave_flag = bond_dev->flags & IFF_SLAVE;
+
+	ether_setup(bond_dev);
+	bond_dev->flags |= IFF_MASTER | slave_flag;
+	bond_dev->priv_flags &= ~IFF_TX_SKB_SHARING;
+}
+
 /* enslave device <slave> to bond device <master> */
 int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev,
 		 struct netlink_ext_ack *extack)

@@ -1777,10 +1790,8 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev,
 
 			if (slave_dev->type != ARPHRD_ETHER)
 				bond_setup_by_slave(bond_dev, slave_dev);
-			else {
-				ether_setup(bond_dev);
-				bond_dev->priv_flags &= ~IFF_TX_SKB_SHARING;
-			}
+			else
+				bond_ether_setup(bond_dev);
 
 			call_netdevice_notifiers(NETDEV_POST_TYPE_CHANGE,
 						 bond_dev);

-- 
2.30.2