[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>

2 files changed, 5 insertions, 14 deletions

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 43af9e9b2652..3f67a29593bc 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -459,19 +459,7 @@ static __init int veth_init(void)
 
 static __exit void veth_exit(void)
 {
-        struct veth_priv *priv, *next;
-
-        rtnl_lock();
-        /*
-         * cannot trust __rtnl_link_unregister() to unregister all
-         * devices, as each ->dellink call will remove two devices
-         * from the list at once.
-         */
-        list_for_each_entry_safe(priv, next, &veth_list, list)
-                veth_dellink(priv->dev);
-
-        __rtnl_link_unregister(&veth_link_ops);
-        rtnl_unlock();
+        rtnl_link_unregister(&veth_link_ops);
 }
 
 module_init(veth_init);
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);