netdev - 答复: [PATCH] ipv6: addrconf: fix dev refcont leak when DAD failed

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Message-ID: <6AADFAC011213A4C87B956458587ADB46B4BE2@SZXEMI508-MBX.china.huawei.com>
Date:   Mon, 5 Sep 2016 11:54:42 +0000
From:   "weiyongjun (A)" <weiyongjun1@...wei.com>
To:     "weiyongjun (A)" <weiyongjun1@...wei.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        "David S. Miller" <davem@...emloft.net>,
        "Alexey Kuznetsov" <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        "Hideaki YOSHIFUJI" <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        Dingtianhong <dingtianhong@...wei.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: 答复: [PATCH] ipv6: addrconf: fix dev refcont leak when DAD failed

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: stable@...r.kernel.org
>>> Fixes: c15b1ccadb32 ("ipv6: move DAD and addrconf_verify processing 
>>> to
>>> workqueue")
>>> Signed-off-by: Wei Yongjun <weiyongjun1@...wei.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.

Regards,
Wei Yongjun