FAILED: patch "[PATCH] net: avoid UAF on deleted altname" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 1a83f4a7c156fa6bbd6b530e89fa3270bf3d9d1b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023102011-rubble-require-8127@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1a83f4a7c156fa6bbd6b530e89fa3270bf3d9d1b Mon Sep 17 00:00:00 2001
From: Jakub Kicinski <[email protected]>
Date: Tue, 17 Oct 2023 18:38:15 -0700
Subject: [PATCH] net: avoid UAF on deleted altname

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

Each node has one or two allocations (node and a variable-size name, sometimes the name is netdev->name). Adding rcu_heads here is a bit tedious. Besides most code which unlists the names already has rcu barriers - so take the simpler approach of adding synchronize_rcu(). Note that the one on the unregistration path (which matters more) is removed by the next fix.

index ae557193b77c..559705aeefe4 100644
@@ -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;

@@ -10941,6 +10942,7 @@ 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. */

@@ -10968,6 +10970,9 @@ 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);