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
> --- a/net/8021q/vlan.c
> +++ 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
> --- a/net/8021q/vlan_core.c
> +++ 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.
RDMA must be calling this helper on a vlan which was already
unregistered, can we fix RDMA instead?
