Messages in this thread | | | Subject | Re: [PATCH net v2] net: vlan: fix a UAF in vlan_dev_real_dev() | From | "Ziyang Xuan (William)" <> | Date | Fri, 19 Nov 2021 11:04:51 +0800 |
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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.
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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