4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Wei Yongjun <weiyongj...@huawei.com>

commit 751eb6b6042a596b0080967c1a529a9fe98dac1d upstream.

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

Fixes: c15b1ccadb32 ("ipv6: move DAD and addrconf_verify processing
to workqueue")
Signed-off-by: Wei Yongjun <weiyongj...@huawei.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 net/ipv6/addrconf.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1898,6 +1898,7 @@ errdad:
        spin_unlock_bh(&ifp->lock);
 
        addrconf_mod_dad_work(ifp, 0);
+       in6_ifa_put(ifp);
 }
 
 /* Join to solicited addr multicast group.
@@ -3609,6 +3610,7 @@ static void addrconf_dad_work(struct wor
                addrconf_dad_begin(ifp);
                goto out;
        } else if (action == DAD_ABORT) {
+               in6_ifa_hold(ifp);
                addrconf_dad_stop(ifp, 1);
                goto out;
        }


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