bonding: fix netdev event NULL pointer dereference

In commit 471cb5a33dcbd7c529684a2ac7ba4451414ee4a7 ("bonding: remove
usage of dev->master") a bug was introduced which causes a NULL pointer
dereference. If a bond device is in mode 6 (ALB) and a slave is added
it will dereference a NULL pointer in bond_slave_netdev_event().
This is because in bond_enslave we have bond_alb_init_slave() which
changes the MAC address of the slave and causes a NETDEV_CHANGEADDR.
Then we have in bond_slave_netdev_event():
        struct slave *slave = bond_slave_get_rtnl(slave_dev);
        struct bonding *bond = slave->bond;
bond_slave_get_rtnl() dereferences slave_dev->rx_handler_data which at
that time is NULL since netdev_rx_handler_register() is called later.

This is fixed by checking if slave is NULL before dereferencing it.

v2: Comment style changed.

Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 07401a3e256bf3b1c5f56c607d80f757b448105a..e074c6b555175395f20ec7bf1eb3664716c54964 100644 (file)
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -3168,11 +3168,20 @@ static int bond_slave_netdev_event(unsigned long event,
                                   struct net_device *slave_dev)
 {
        struct slave *slave = bond_slave_get_rtnl(slave_dev);
-       struct bonding *bond = slave->bond;
-       struct net_device *bond_dev = slave->bond->dev;
+       struct bonding *bond;
+       struct net_device *bond_dev;
        u32 old_speed;
        u8 old_duplex;
 
+       /* A netdev event can be generated while enslaving a device
+        * before netdev_rx_handler_register is called in which case
+        * slave will be NULL
+        */
+       if (!slave)
+               return NOTIFY_DONE;
+       bond_dev = slave->bond->dev;
+       bond = slave->bond;
+
        switch (event) {
        case NETDEV_UNREGISTER:
                if (bond->setup_by_slave)