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

Ziyang Xuan (William) <william.xuanziyang@huawei.com> writes:

>>
>> Ziyang Xuan (William) <william.xuanziyang@huawei.com> writes:
>>
>>> I need some time to test my some ideas. And anyone has good ideas, please
>>> do not be stingy.
>>
>> Jakub Kicinski <kuba@kernel.org> writes:
>>
>>> I think we should move the dev_hold() to ndo_init(), otherwise it's
>>> hard to reason if destructor was invoked or not if
>>> register_netdevice() errors out.
>>
>> That makes sense to me. We always put real_dev in the destructor, so we
>> should always hold it in the constructor...
>
> Inject error before dev_hold(real_dev) in register_vlan_dev(), and execute
> the following testcase:
>
> ip link add dev dummy1 type dummy
> ip link add name dummy1.100 link dummy1 type vlan id 100 // failed for error injection
> ip link del dev dummy1
>
> Make the problem repro. The problem is solved using the following fix
> according to the Jakub's suggestion:
>
> diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
> index a3a0a5e994f5..abaa5d96ded2 100644
> --- a/net/8021q/vlan.c
> +++ b/net/8021q/vlan.c
> @@ -184,9 +184,6 @@ int register_vlan_dev(struct net_device *dev, struct netlink_ext_ack *extack)
> if (err)
> goto out_unregister_netdev;
>
> - /* Account for reference in struct vlan_dev_priv */
> - dev_hold(real_dev);
> -
> vlan_stacked_transfer_operstate(real_dev, dev, vlan);
> linkwatch_fire_event(dev); /* _MUST_ call rfc2863_policy() */
>
> diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
> index ab6dee28536d..a54535cbcf4c 100644
> --- a/net/8021q/vlan_dev.c
> +++ b/net/8021q/vlan_dev.c
> @@ -615,6 +615,9 @@ static int vlan_dev_init(struct net_device *dev)
> if (!vlan->vlan_pcpu_stats)
> return -ENOMEM;
>
> + /* Get vlan's reference to real_dev */
> + dev_hold(real_dev);
>
>
> If there is not any other idea and objection, I will send the fix patch later.
>
> Thank you!

This fixes the issue in my repro, and does not seems to break anything.
We'll take it to full regression overnight, I'll report back tomorrow
about the result.

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