[PATCH AUTOSEL for 4.9 36/52] macvlan: Fix one possible double free

[Sasha Levin]

From: Gao Feng <gfree.wind@xxxxxxxxxxx>

[ Upstream commit d02fd6e7d2933ede6478a15f9e4ce8a93845824e ]

Because the macvlan_uninit would free the macvlan port, so there is one
double free case in macvlan_common_newlink. When the macvlan port is just
created, then register_netdevice or netdev_upper_dev_link failed and they
would invoke macvlan_uninit. Then it would reach the macvlan_port_destroy
which triggers the double free.

Signed-off-by: Gao Feng <gfree.wind@xxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 drivers/net/macvlan.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index 6d55049cd3dc..e8ad4d060da7 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -1377,9 +1377,14 @@ int macvlan_common_newlink(struct net *src_net, struct net_device *dev,
 	return 0;
 
 unregister_netdev:
+	/* macvlan_uninit would free the macvlan port */
 	unregister_netdevice(dev);
+	return err;
 destroy_macvlan_port:
-	if (create)
+	/* the macvlan port may be freed by macvlan_uninit when fail to register.
+	 * so we destroy the macvlan port only when it's valid.
+	 */
+	if (create && macvlan_port_get_rtnl(dev))
 		macvlan_port_destroy(port->dev);
 	return err;
 }
-- 
2.11.0