net: fix use-after-free in the netdev_nl_sock_priv_destroy()

In the netdev_nl_sock_priv_destroy(), an instance lock is acquired
before calling net_devmem_unbind_dmabuf(), then releasing an instance
lock(netdev_unlock(binding->dev)).
However, a binding is freed in the net_devmem_unbind_dmabuf().
So using a binding after net_devmem_unbind_dmabuf() occurs UAF.
To fix this UAF, it needs to use temporary variable.

Fixes: ba6f418 ("net: bubble up taking netdev instance lock to callers of net_devmem_unbind_dmabuf()")
Signed-off-by: Taehee Yoo <[email protected]>
Reviewed-by: Jakub Kicinski <[email protected]>
Reviewed-by: Mina Almasry <[email protected]>
Reviewed-by: Xuan Zhuo <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: TaeheeYoo

net/core/netdev-genl.c

@@ -951,12 +951,14 @@ void netdev_nl_sock_priv_destroy(struct netdev_nl_sock *priv)
 {
 	struct net_devmem_dmabuf_binding *binding;
 	struct net_devmem_dmabuf_binding *temp;
+	struct net_device *dev;
 
 	mutex_lock(&priv->lock);
 	list_for_each_entry_safe(binding, temp, &priv->bindings, list) {
-		netdev_lock(binding->dev);
+		dev = binding->dev;
+		netdev_lock(dev);
 		net_devmem_unbind_dmabuf(binding);
-		netdev_unlock(binding->dev);
+		netdev_unlock(dev);
 	}
 	mutex_unlock(&priv->lock);
 }