vxlan: fix unexpected failure of vxlan_changelink()

After commit 0ce1822c2a08 ("vxlan: add adjacent link to limit depth
level"), vxlan_changelink() could fail because of
netdev_adjacent_change_prepare().
netdev_adjacent_change_prepare() returns -EEXIST when old lower device
and new lower device are same.
(old lower device is "dst->remote_dev" and new lower device is "lowerdev")
So, before calling it, lowerdev should be NULL if these devices are same.

Test command1:
    ip link add dummy0 type dummy
    ip link add vxlan0 type vxlan dev dummy0 dstport 4789 vni 1
    ip link set vxlan0 type vxlan ttl 5
    RTNETLINK answers: File exists

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 0ce1822c2a08 ("vxlan: add adjacent link to limit depth level")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index ac5c597..8869154 100644 (file)
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -3967,6 +3967,9 @@ static int vxlan_changelink(struct net_device *dev, struct nlattr *tb[],
        if (err)
                return err;
 
+       if (dst->remote_dev == lowerdev)
+               lowerdev = NULL;
+
        err = netdev_adjacent_change_prepare(dst->remote_dev, lowerdev, dev,
                                             extack);
        if (err)
@@ -4008,10 +4011,10 @@ static int vxlan_changelink(struct net_device *dev, struct nlattr *tb[],
                mod_timer(&vxlan->age_timer, jiffies);
 
        netdev_adjacent_change_commit(dst->remote_dev, lowerdev, dev);
-       if (lowerdev && lowerdev != dst->remote_dev)
+       if (lowerdev && lowerdev != dst->remote_dev) {
                dst->remote_dev = lowerdev;
-
-       netdev_update_lockdep_key(lowerdev);
+               netdev_update_lockdep_key(lowerdev);
+       }
        vxlan_config_apply(dev, &conf, lowerdev, vxlan->net, true);
        return 0;
 }