[PATCH net 3/5] net: avoid UAF on deleted altname

[Jakub Kicinski <kuba@kernel.org>]

Altnames are accessed under RCU (__dev_get_by_name())
but freed by kfree() with no synchronization point.

Because the name nodes don't hold a reference on the netdevice
either, take the heavier approach of inserting synchronization
points. Subsequent patch will remove the one added on device
deletion path.

Fixes: ff92741270bf ("net: introduce name_node struct to be used in hashlist")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: jiri@resnulli.us
---
 net/core/dev.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index f4fa2692cf6d..7d5107cd5792 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -345,7 +345,6 @@ int netdev_name_node_alt_create(struct net_device *dev, const char *name)
 static void __netdev_name_node_alt_destroy(struct netdev_name_node *name_node)
 {
 	list_del(&name_node->list);
-	netdev_name_node_del(name_node);
 	kfree(name_node->name);
 	netdev_name_node_free(name_node);
 }
@@ -364,6 +363,8 @@ int netdev_name_node_alt_destroy(struct net_device *dev, const char *name)
 	if (name_node == dev->name_node || name_node->dev != dev)
 		return -EINVAL;
 
+	netdev_name_node_del(name_node);
+	synchronize_rcu();
 	__netdev_name_node_alt_destroy(name_node);
 
 	return 0;
@@ -10937,6 +10938,7 @@ void unregister_netdevice_many_notify(struct list_head *head,
 	synchronize_net();
 
 	list_for_each_entry(dev, head, unreg_list) {
+		struct netdev_name_node *name_node;
 		struct sk_buff *skb = NULL;
 
 		/* Shutdown queueing discipline. */
@@ -10964,6 +10966,9 @@ void unregister_netdevice_many_notify(struct list_head *head,
 		dev_uc_flush(dev);
 		dev_mc_flush(dev);
 
+		netdev_for_each_altname(dev, name_node)
+			netdev_name_node_del(name_node);
+		synchronize_rcu();
 		netdev_name_node_alt_flush(dev);
 		netdev_name_node_free(dev->name_node);
 
-- 
2.41.0