FAILED: patch "[PATCH] vlan: move dev_put into vlan_dev_uninit" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

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 <stable@vger.kernel.org>.

thanks,

greg k-h

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

From d6ff94afd90b0ce8d1715f8ef77d4347d7a7f2c0 Mon Sep 17 00:00:00 2001
From: Xin Long <lucien.xin@gmail.com>
Date: Wed, 9 Feb 2022 03:19:56 -0500
Subject: [PATCH] vlan: move dev_put into vlan_dev_uninit

Shuang Li reported an QinQ issue by simply doing:

  # ip link add dummy0 type dummy
  # ip link add link dummy0 name dummy0.1 type vlan id 1
  # ip link add link dummy0.1 name dummy0.1.2 type vlan id 2
  # rmmod 8021q

 unregister_netdevice: waiting for dummy0.1 to become free. Usage count = 1

When rmmods 8021q, all vlan devs are deleted from their real_dev's vlan grp
and added into list_kill by unregister_vlan_dev(). dummy0.1 is unregistered
before dummy0.1.2, as it's using for_each_netdev() in __rtnl_kill_links().

When unregisters dummy0.1, dummy0.1.2 is not unregistered in the event of
NETDEV_UNREGISTER, as it's been deleted from dummy0.1's vlan grp. However,
due to dummy0.1.2 still holding dummy0.1, dummy0.1 will keep waiting in
netdev_wait_allrefs(), while dummy0.1.2 will never get unregistered and
release dummy0.1, as it delays dev_put until calling dev->priv_destructor,
vlan_dev_free().

This issue was introduced by Commit 563bcbae3ba2 ("net: vlan: fix a UAF in
vlan_dev_real_dev()"), and this patch is to fix it by moving dev_put() into
vlan_dev_uninit(), which is called after NETDEV_UNREGISTER event but before
netdev_wait_allrefs().

Fixes: 563bcbae3ba2 ("net: vlan: fix a UAF in vlan_dev_real_dev()")
Reported-by: Shuang Li <shuali@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
index e5d23e75572a..d1902828a18a 100644
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -638,7 +638,12 @@ void vlan_dev_free_egress_priority(const struct net_device *dev)
 
 static void vlan_dev_uninit(struct net_device *dev)
 {
+	struct vlan_dev_priv *vlan = vlan_dev_priv(dev);
+
 	vlan_dev_free_egress_priority(dev);
+
+	/* Get rid of the vlan's reference to real_dev */
+	dev_put_track(vlan->real_dev, &vlan->dev_tracker);
 }
 
 static netdev_features_t vlan_dev_fix_features(struct net_device *dev,
@@ -851,9 +856,6 @@ static void vlan_dev_free(struct net_device *dev)
 
 	free_percpu(vlan->vlan_pcpu_stats);
 	vlan->vlan_pcpu_stats = NULL;
-
-	/* Get rid of the vlan's reference to real_dev */
-	dev_put_track(vlan->real_dev, &vlan->dev_tracker);
 }
 
 void vlan_setup(struct net_device *dev)