On 05.09.2016 13:54, weiyongjun (A) wrote:
> On 05.09.2016 10:06, Wei Yongjun wrote:
>>>> 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: sta...@vger.kernel.org
>>>> Fixes: c15b1ccadb32 ("ipv6: move DAD and addrconf_verify processing
>>>> to
>>>> workqueue")
>>>> Signed-off-by: Wei Yongjun <weiyongj...@huawei.com>
>>>>
>>>> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index
>>>> bdf368e..2f1f5d4 100644
>>>> --- a/net/ipv6/addrconf.c
>>>> +++ b/net/ipv6/addrconf.c
>>>> @@ -1948,6 +1948,7 @@ errdad:
>>>> spin_unlock_bh(&ifp->lock);
>>>>
>>>> addrconf_mod_dad_work(ifp, 0);
>>>> + in6_ifa_put(ifp);
>>>> }
>
>>> This in6_ifa_put makes sense.
>
>>>>
>>>> /* Join to solicited addr multicast group.
>>>> @@ -3857,6 +3858,7 @@ static void addrconf_dad_work(struct work_struct *w)
>>>> addrconf_dad_begin(ifp);
>>>> goto out;
>>>> } else if (action == DAD_ABORT) {
>>>> + in6_ifa_hold(ifp);
>>>> addrconf_dad_stop(ifp, 1);
>>>> if (disable_ipv6)
>>>> addrconf_ifdown(idev->dev, 0);
>>>>
>
>>> But why you add a in6_ifa_hold here isn't clear to me. Could you
>>> explain why this is necessary? I don't see any async stuff being done
>>> in addrconf_dad_stop, thus the reference we already have should be
>>> sufficient for the lifetime of addrconf_dad_stop.
>
>> I think it that link local is added with flag IFA_F_PERMANENT, which we real
>> need it is to remove in6_ifa_put() in addrconf_dad_stop.
>
>> static void addrconf_dad_stop(...)
>> {
>> if (ifp->flags&IFA_F_PERMANENT) {
>> ...
>> in6_ifa_put(ifp); <== remove this line since caller hold
>> refcount
>> } else if (ifp->flags&IFA_F_TEMPORARY) {
>> ...
>> ipv6_del_addr(ifp);
>> } else {
>> ipv6_del_addr(ifp);
>> }
>> }
>
> I see the comment of ipv6_del_addr:
>
> /* This function wants to get referenced ifp and releases it before return */
> static void ipv6_del_addr(struct inet6_ifaddr *ifp)
> {
> ...
> }
>
> Both in6_ifa_put() and ipv6_del_addr() need a refcount holding, so we should
> use a extra in6_ifa_hold() call before call addrconf_dad_stop() as the origin
> patch.
You are correct!
We always call in6_ifa_put() at the end of addrconf_dad_work. In this
case it is not correct. Either we add a in6_ifa_hold or we suppress or
jump over the last in6_ifa_put.
Good catch!
Hannes
