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

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Nov 02, 2021 at 10:12:18AM +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
> ...
> 
> Move the put_device(real_dev) to vlan_dev_free(). Ensure
> real_dev not be freed before vlan_dev unregistered.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: syzbot+e4df4e1389e28972e955@syzkaller.appspotmail.com
> Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
> ---
>  net/8021q/vlan.c     | 3 ---
>  net/8021q/vlan_dev.c | 3 +++
>  2 files changed, 3 insertions(+), 3 deletions(-)

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

(though I can't tell either if there is a possiblecircular dep problem
in some oddball case)

Jason