On Wed, Oct 27, 2021 at 06:46:40PM -0700, Jakub Kicinski wrote:
> On Wed, 27 Oct 2021 20:16:06 +0800 Ziyang Xuan wrote:
> > The real_dev of a vlan net_device may be freed after
> > unregister_vlan_dev(). Access the real_dev continually by
> > vlan_dev_real_dev() will trigger the UAF problem for the
> > real_dev like following:
> >
> > ==================================================================
> > BUG: KASAN: use-after-free in vlan_dev_real_dev+0xf9/0x120
> > Call Trace:
> > kasan_report.cold+0x83/0xdf
> > vlan_dev_real_dev+0xf9/0x120
> > is_eth_port_of_netdev_filter.part.0+0xb1/0x2c0
> > is_eth_port_of_netdev_filter+0x28/0x40
> > ib_enum_roce_netdev+0x1a3/0x300
> > ib_enum_all_roce_netdevs+0xc7/0x140
> > netdevice_event_work_handler+0x9d/0x210
> > ...
> >
> > Freed by task 9288:
> > kasan_save_stack+0x1b/0x40
> > kasan_set_track+0x1c/0x30
> > kasan_set_free_info+0x20/0x30
> > __kasan_slab_free+0xfc/0x130
> > slab_free_freelist_hook+0xdd/0x240
> > kfree+0xe4/0x690
> > kvfree+0x42/0x50
> > device_release+0x9f/0x240
> > kobject_put+0x1c8/0x530
> > put_device+0x1b/0x30
> > free_netdev+0x370/0x540
> > ppp_destroy_interface+0x313/0x3d0
> > ...
> >
> > Set vlan->real_dev to NULL after dev_put(real_dev) in
> > unregister_vlan_dev(). Check real_dev is not NULL before
> > access it in vlan_dev_real_dev().
> >
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Reported-by: syzbot+e4df4e1389e28972e955@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>
> > net/8021q/vlan.c | 1 +
> > net/8021q/vlan_core.c | 2 +-
> > 2 files changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
> > index 55275ef9a31a..1106da84e725 100644
> > +++ b/net/8021q/vlan.c
> > @@ -126,6 +126,7 @@ void unregister_vlan_dev(struct net_device *dev, struct list_head *head)
> >
> > /* Get rid of the vlan's reference to real_dev */
> > dev_put(real_dev);
> > + vlan->real_dev = NULL;
> > }
> >
> > int vlan_check_real_dev(struct net_device *real_dev,
> > diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
> > index 59bc13b5f14f..343f34479d8b 100644
> > +++ b/net/8021q/vlan_core.c
> > @@ -103,7 +103,7 @@ struct net_device *vlan_dev_real_dev(const struct net_device *dev)
> > {
> > struct net_device *ret = vlan_dev_priv(dev)->real_dev;
> >
> > - while (is_vlan_dev(ret))
> > + while (ret && is_vlan_dev(ret))
> > ret = vlan_dev_priv(ret)->real_dev;
> >
> > return ret;
>
> But will make all the callers of vlan_dev_real_dev() feel like they
> should NULL-check the result, which is not necessary.
Isn't it better to reliably return NULL instead of a silent UAF in
this edge case?
> RDMA must be calling this helper on a vlan which was already
> unregistered, can we fix RDMA instead?
RDMA holds a get on the netdev which prevents unregistration, however
unregister_vlan_dev() does:
unregister_netdevice_queue(dev, head);
dev_put(real_dev);
Which corrupts the still registered vlan device while it is sitting in
the queue waiting to unregister. So, it is not true that a registered
vlan device always has working vlan_dev_real_dev().
Jason
