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SubjectRe: [PATCH net v2] net: vlan: fix a UAF in vlan_dev_real_dev()
From
Date
> 
> 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.

netdev_upper_dev_link() failure in register_vlan_dev() will result in
no dev_hold(real_dev) and vlan_group_set_device(). So NETDEV_UNREGISTER
notifier caused by vlan_dev invokes vlan_device_event() will not find the
vlan_dev in vlan_group, and no unregister_vlan_dev() for the vlan_dev.

>

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