[PATCH] netdevsim: remove debugfs files before freeing net_device
From: "syzbot" <syzbot@kernel.org>
Date: 2026-06-27 11:20:12
Also in:
lkml, syzbot
Subsystem:
netdevsim, networking drivers, the rest · Maintainers:
Jakub Kicinski, Andrew Lunn, "David S. Miller", Eric Dumazet, Paolo Abeni, Linus Torvalds
From: Aleksandr Nogikh <redacted>
A KASAN slab-use-after-free was detected in debugfs_u32_get() when reading
a debugfs file associated with a netdevsim port.
BUG: KASAN: slab-use-after-free in debugfs_u32_get+0x6c/0x70
Read of size 4 at addr ffff88810cd6db00
Call Trace:
debugfs_u32_get+0x6c/0x70
simple_attr_read+0x227/0x490
debugfs_attr_read+0x76/0x130
vfs_read+0x213/0xa80
The root cause is that the net_device (and its embedded netdevsim private
data) is freed before its associated debugfs files are removed. When a user
reads a debugfs file like rx_max_pending, debugfs_u32_get() dereferences a
pointer to the freed memory. This happens because nsim_destroy() calls
free_netdev() but does not remove the debugfs files created by
nsim_ethtool_init() or nsim_bpf_init(). These files are only removed later
when nsim_dev_port_debugfs_exit() is called. A similar issue exists in the
error path of nsim_create().
To fix this, swap the teardown order in __nsim_dev_port_del() and the
__nsim_dev_port_add() error path so that nsim_dev_port_debugfs_exit() is
called before nsim_destroy(). This ensures the debugfs directory is
recursively removed before the net_device is freed. Additionally, remove
explicit debugfs_remove() calls from various subsystem teardown functions
(like nsim_psp_uninit, nsim_ipsec_teardown, etc.) since the parent
directory is now removed earlier, which would otherwise lead to a
use-after-free of the dentry itself. Finally, ensure the debugfs directory
is removed before free_netdev() is called in the nsim_create() error path.
Fixes: e05b2d141fef ("netdevsim: move netdev creation/destruction to dev probe")
Assisted-by: Gemini:gemini-3.1-pro-preview Gemini:gemini-3-flash-preview syzbot
Reported-by: syzbot+6c25f4750230faf70be9@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6c25f4750230faf70be9
Link: https://syzkaller.appspot.com/ai_job?id=f0f1a72a-a527-478e-a31c-7b83cdfee8d1
Signed-off-by: Aleksandr Nogikh <redacted>
---diff --git a/drivers/net/netdevsim/dev.c b/drivers/net/netdevsim/dev.c
index f00fc2f9e..4c2c9aa1e 100644
--- a/drivers/net/netdevsim/dev.c
+++ b/drivers/net/netdevsim/dev.c@@ -1516,17 +1516,17 @@ static int __nsim_dev_port_add(struct nsim_dev *nsim_dev, enum nsim_dev_port_typ err = devl_rate_leaf_create(&nsim_dev_port->devlink_port, nsim_dev_port, NULL); if (err) - goto err_nsim_destroy; + goto err_port_debugfs_exit; } list_add(&nsim_dev_port->list, &nsim_dev->port_list); return 0; -err_nsim_destroy: - nsim_destroy(nsim_dev_port->ns); err_port_debugfs_exit: nsim_dev_port_debugfs_exit(nsim_dev_port); + if (!IS_ERR_OR_NULL(nsim_dev_port->ns)) + nsim_destroy(nsim_dev_port->ns); err_port_resource_unregister: if (nsim_dev_port_is_pf(nsim_dev_port)) devl_port_resources_unregister(devlink_port);
@@ -1544,8 +1544,8 @@ static void __nsim_dev_port_del(struct nsim_dev_port *nsim_dev_port) list_del(&nsim_dev_port->list); if (nsim_dev_port_is_vf(nsim_dev_port)) devl_rate_leaf_destroy(&nsim_dev_port->devlink_port); - nsim_destroy(nsim_dev_port->ns); nsim_dev_port_debugfs_exit(nsim_dev_port); + nsim_destroy(nsim_dev_port->ns); if (nsim_dev_port_is_pf(nsim_dev_port)) devl_port_resources_unregister(devlink_port); devl_port_unregister(devlink_port);
diff --git a/drivers/net/netdevsim/ipsec.c b/drivers/net/netdevsim/ipsec.c
index 36a1be492..0bc9f42a5 100644
--- a/drivers/net/netdevsim/ipsec.c
+++ b/drivers/net/netdevsim/ipsec.c@@ -292,5 +292,4 @@ void nsim_ipsec_teardown(struct netdevsim *ns) if (ipsec->count) netdev_err(ns->netdev, "tearing down IPsec offload with %d SAs left\n", ipsec->count); - debugfs_remove_recursive(ipsec->pfile); }
diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index a75076891..240107369 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c@@ -1154,16 +1154,17 @@ struct netdevsim *nsim_create(struct nsim_dev *nsim_dev, if (err) goto err_free_netdev; - ns->pp_dfs = debugfs_create_file("pp_hold", 0600, nsim_dev_port->ddir, - ns, &nsim_pp_hold_fops); - ns->qr_dfs = debugfs_create_file("queue_reset", 0200, - nsim_dev_port->ddir, ns, - &nsim_qreset_fops); - ns->vlan_dfs = debugfs_create_file("vlan", 0400, nsim_dev_port->ddir, - ns, &nsim_vlan_fops); + debugfs_create_file("pp_hold", 0600, nsim_dev_port->ddir, ns, + &nsim_pp_hold_fops); + debugfs_create_file("queue_reset", 0200, nsim_dev_port->ddir, ns, + &nsim_qreset_fops); + debugfs_create_file("vlan", 0400, nsim_dev_port->ddir, ns, + &nsim_vlan_fops); return ns; err_free_netdev: + debugfs_remove_recursive(nsim_dev_port->ddir); + nsim_dev_port->ddir = NULL; free_netdev(dev); return ERR_PTR(err); }
@@ -1174,10 +1175,6 @@ void nsim_destroy(struct netdevsim *ns) struct netdevsim *peer; u16 vid; - debugfs_remove(ns->vlan_dfs); - debugfs_remove(ns->qr_dfs); - debugfs_remove(ns->pp_dfs); - if (ns->nb.notifier_call) unregister_netdevice_notifier_dev_net(ns->netdev, &ns->nb, &ns->nn);
diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h
index d909c4160..29cbf004a 100644
--- a/drivers/net/netdevsim/netdevsim.h
+++ b/drivers/net/netdevsim/netdevsim.h@@ -153,9 +153,6 @@ struct netdevsim { } udp_ports; struct page *page; - struct dentry *pp_dfs; - struct dentry *qr_dfs; - struct dentry *vlan_dfs; struct nsim_ethtool ethtool; struct netdevsim __rcu *peer;
diff --git a/drivers/net/netdevsim/psp.c b/drivers/net/netdevsim/psp.c
index 6936ecb81..2f27a2114 100644
--- a/drivers/net/netdevsim/psp.c
+++ b/drivers/net/netdevsim/psp.c@@ -227,7 +227,6 @@ static void __nsim_psp_uninit(struct netdevsim *ns, bool teardown) void nsim_psp_uninit(struct netdevsim *ns) { - debugfs_remove(ns->psp.rereg); mutex_destroy(&ns->psp.rereg_lock); __nsim_psp_uninit(ns, true); }
diff --git a/drivers/net/netdevsim/udp_tunnels.c b/drivers/net/netdevsim/udp_tunnels.c
index 89fff76e5..a69b15f12 100644
--- a/drivers/net/netdevsim/udp_tunnels.c
+++ b/drivers/net/netdevsim/udp_tunnels.c@@ -188,9 +188,6 @@ int nsim_udp_tunnels_info_create(struct nsim_dev *nsim_dev, void nsim_udp_tunnels_info_destroy(struct net_device *dev) { - struct netdevsim *ns = netdev_priv(dev); - - debugfs_remove_recursive(ns->udp_ports.ddir); kfree(dev->udp_tunnel_nic_info); dev->udp_tunnel_nic_info = NULL; }
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