Re: [PATCH net v2] net: vlan: fix a UAF in vlan_dev_real_dev()
From: Petr Machata <petrm@nvidia.com>
Date: 2021-11-15 17:06:13
Also in:
lkml
Ziyang Xuan [off-list ref] writes:
quoted hunk ↗ jump to hunk
diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c index 55275ef9a31a..a3a0a5e994f5 100644 --- a/net/8021q/vlan.c +++ b/net/8021q/vlan.c@@ -123,9 +123,6 @@ void unregister_vlan_dev(struct net_device *dev, struct list_head *head) } vlan_vid_del(real_dev, vlan->vlan_proto, vlan_id); - - /* Get rid of the vlan's reference to real_dev */ - dev_put(real_dev); } int vlan_check_real_dev(struct net_device *real_dev,diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c index 0c21d1fec852..aeeb5f90417b 100644 --- a/net/8021q/vlan_dev.c +++ b/net/8021q/vlan_dev.c@@ -843,6 +843,9 @@ 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(vlan->real_dev); } void vlan_setup(struct net_device *dev)
This is causing reference counting issues when vetoing is involved.
Consider the following snippet:
ip link add name bond1 type bond mode 802.3ad
ip link set dev swp1 master bond1
ip link add name bond1.100 link bond1 type vlan protocol 802.1ad id 100
# ^ vetoed, no netdevice created
ip link del dev bond1
The setup process goes like this: vlan_newlink() calls
register_vlan_dev() calls netdev_upper_dev_link() calls
__netdev_upper_dev_link(), which issues a notifier
NETDEV_PRECHANGEUPPER, which yields a non-zero error,
because a listener vetoed it.
So it unwinds, skipping dev_hold(real_dev), but eventually the VLAN ends
up decreasing reference count of the real_dev. Then when when the bond
netdevice is removed, we get an endless loop of:
kernel:unregister_netdevice: waiting for bond1 to become free. Usage count = 0
Moving the dev_hold(real_dev) to always happen even if the
netdev_upper_dev_link() call makes the issue go away.
I'm not sure why this wasn't happening before. After the veto,
register_vlan_dev() follows with a goto out_unregister_netdev, which
calls unregister_netdevice() calls unregister_netdevice_queue(), which
issues a notifier NETDEV_UNREGISTER, which invokes vlan_device_event(),
which calls unregister_vlan_dev(), which used to dev_put(real_dev),
which seems like it should have caused the same issue. Dunno.