Messages in this thread | | | From | Petr Machata <> | Subject | Re: [PATCH net v2] net: vlan: fix a UAF in vlan_dev_real_dev() | Date | Wed, 17 Nov 2021 12:50:59 +0100 |
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Jakub Kicinski <kuba@kernel.org> writes:
> On Mon, 15 Nov 2021 18:04:42 +0100 Petr Machata wrote: >> 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 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.
Ziyang Xuan, do you intend to take care of this?
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