Re: [PATCH] ipv6: addrconf: fix dev refcont leak when DAD failed

[David Miller <davem@davemloft.net>]

From: Wei Yongjun <weiyongjun1@huawei.com>
Date: Mon, 5 Sep 2016 16:06:31 +0800

> In general, when DAD detected IPv6 duplicate address, ifp->state
> will be set to INET6_IFADDR_STATE_ERRDAD and DAD is stopped by a
> delayed work, the call tree should be like this:
> 
> ndisc_recv_ns
>   -> addrconf_dad_failure        <- missing ifp put
>      -> addrconf_mod_dad_work
>        -> schedule addrconf_dad_work()
>          -> addrconf_dad_stop()  <- missing ifp hold before call it
> 
> addrconf_dad_failure() called with ifp refcont holding but not put.
> addrconf_dad_work() call addrconf_dad_stop() without extra holding
> refcount. This will not cause any issue normally.
> 
> But the race between addrconf_dad_failure() and addrconf_dad_work()
> may cause ifp refcount leak and netdevice can not be unregister,
> dmesg show the following messages:
> 
> IPv6: eth0: IPv6 duplicate address fe80::XX:XXXX:XXXX:XX detected!
> ...
> unregister_netdevice: waiting for eth0 to become free. Usage count = 1
> 
> Cc: stable@vger.kernel.org
> Fixes: c15b1ccadb32 ("ipv6: move DAD and addrconf_verify processing
> to workqueue")
> Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>

Applied and queued up for -stable.