[NET]: rtnl_link: fix use-after-free

When unregistering the rtnl_link_ops, all existing devices using
the ops are destroyed. With nested devices this may lead to a
use-after-free despite the use of for_each_netdev_safe() in case
the upper device is next in the device list and is destroyed
by the NETDEV_UNREGISTER notifier.

The easy fix is to restart scanning the device list after removing
a device. Alternatively we could add new devices to the front of
the list to avoid having dependant devices follow the device they
depend on. A third option would be to only restart scanning if
dev->iflink of the next device matches dev->ifindex of the current
one. For now this seems like the safest solution.

With this patch, the veth rtnl_link_ops unregistration can use
rtnl_link_unregister() directly since it now also handles destruction
of multiple devices at once.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 1 deletions

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index e1ba26fb4bf2..fed95a323b28 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -308,9 +308,12 @@ void __rtnl_link_unregister(struct rtnl_link_ops *ops)
 	struct net *net;
 
 	for_each_net(net) {
+restart:
 		for_each_netdev_safe(net, dev, n) {
-			if (dev->rtnl_link_ops == ops)
+			if (dev->rtnl_link_ops == ops) {
 				ops->dellink(dev);
+				goto restart;
+			}
 		}
 	}
 	list_del(&ops->list);