[Bridge] [PATCH net] net: bridge: fix per-port vlan stats use-after-free on destruction

[Nikolay Aleksandrov]

On 11/13/18 3:01 AM, Nikolay Aleksandrov wrote:
> Syzbot reported a use-after-free of the global vlan context on port vlan
> destruction. When I added per-port vlan stats I missed the fact that the
> global vlan context can be freed before the per-port vlan rcu callback.
> There're a few different ways to deal with this, I've chosen to add a
> new private flag that is set only when per-port stats are allocated so
> we can directly check it on destruction without dereferencing the global
> context at all. The flag is internally controlled by the kernel and
> user-space isn't allowed to set it.
> 
> Fixes: 9163a0fc1f0c ("net: bridge: add support for per-port vlan stats")
> Reported-by: syzbot+04681da557a0e49a52e5 at syzkaller.appspotmail.com
> Signed-off-by: Nikolay Aleksandrov <nikolay at cumulusnetworks.com>
> ---

I'll post v2 with a cosmetic change - move the check up one level where
it's more logical to be and the rest of the checks are done.