[PATCH] netdevsim: remove ethtool debugfs files before freeing netdev

[Yousef Alhouseen]

The ethtool debugfs files point directly into struct netdevsim, which is
allocated as net_device private data. Their containing port directory is
removed only after nsim_destroy() calls free_netdev().

An open simple-attribute file can consequently dereference the freed
private data before the directory is removed. KASAN observed this in
debugfs_u32_get() during network namespace teardown.

Track and remove the ethtool subtree before free_netdev() on both the
normal and registration-failure paths. debugfs removal drains active
file users before returning.

Fixes: ff1f7c17fb20 ("netdevsim: add pause frame stats")
Reported-by: syzbot+6c25f4750230faf70be9@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=6c25f4750230faf70be9
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Yousef Alhouseen <alhouseenyousef@xxxxxxxxx>
---
 drivers/net/netdevsim/ethtool.c   | 6 ++++++
 drivers/net/netdevsim/netdev.c    | 2 ++
 drivers/net/netdevsim/netdevsim.h | 2 ++
 3 files changed, 10 insertions(+)

diff --git a/drivers/net/netdevsim/ethtool.c b/drivers/net/netdevsim/ethtool.c
index 9350ba48eb81..025ea79879f3 100644
--- a/drivers/net/netdevsim/ethtool.c
+++ b/drivers/net/netdevsim/ethtool.c
@@ -252,6 +252,7 @@ void nsim_ethtool_init(struct netdevsim *ns)
 	ns->ethtool.channels = ns->nsim_bus_dev->num_queues;
 
 	ethtool = debugfs_create_dir("ethtool", ns->nsim_dev_port->ddir);
+	ns->ethtool_ddir = ethtool;
 
 	debugfs_create_u32("get_err", 0600, ethtool, &ns->ethtool.get_err);
 	debugfs_create_u32("set_err", 0600, ethtool, &ns->ethtool.set_err);
@@ -272,3 +273,8 @@ void nsim_ethtool_init(struct netdevsim *ns)
 	debugfs_create_u32("tx_max_pending", 0600, dir,
 			   &ns->ethtool.ring.tx_max_pending);
 }
+
+void nsim_ethtool_fini(struct netdevsim *ns)
+{
+	debugfs_remove(ns->ethtool_ddir);
+}
diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index 27e5f109f933..4e9d7e10b527 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -1165,6 +1165,7 @@ struct netdevsim *nsim_create(struct nsim_dev *nsim_dev,
 	return ns;
 
 err_free_netdev:
+	nsim_ethtool_fini(ns);
 	free_netdev(dev);
 	return ERR_PTR(err);
 }
@@ -1178,6 +1179,7 @@ void nsim_destroy(struct netdevsim *ns)
 	debugfs_remove(ns->vlan_dfs);
 	debugfs_remove(ns->qr_dfs);
 	debugfs_remove(ns->pp_dfs);
+	nsim_ethtool_fini(ns);
 
 	if (ns->nb.notifier_call)
 		unregister_netdevice_notifier_dev_net(ns->netdev, &ns->nb,
diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h
index 4c9cc96dcec3..64f77f93d937 100644
--- a/drivers/net/netdevsim/netdevsim.h
+++ b/drivers/net/netdevsim/netdevsim.h
@@ -154,6 +154,7 @@ struct netdevsim {
 	struct dentry *pp_dfs;
 	struct dentry *qr_dfs;
 	struct dentry *vlan_dfs;
+	struct dentry *ethtool_ddir;
 
 	struct nsim_ethtool ethtool;
 	struct netdevsim __rcu *peer;
@@ -169,6 +170,7 @@ void nsim_destroy(struct netdevsim *ns);
 bool netdev_is_nsim(struct net_device *dev);
 
 void nsim_ethtool_init(struct netdevsim *ns);
+void nsim_ethtool_fini(struct netdevsim *ns);
 
 void nsim_udp_tunnels_debugfs_create(struct nsim_dev *nsim_dev);
 int nsim_udp_tunnels_info_create(struct nsim_dev *nsim_dev,
-- 
2.54.0