Messages in this thread | | | From | Petr Machata <> | Subject | Re: [PATCH net v2] net: vlan: fix a UAF in vlan_dev_real_dev() | Date | Mon, 15 Nov 2021 18:04:42 +0100 |
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Ziyang Xuan <william.xuanziyang@huawei.com> writes:
> 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.
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