netdev - Re: [PATCH net] ipv4: igmp: fix a use after free

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Message-ID: <CADvbK_dQuFY0-3OgDykK=oL+EO4T-Oyr1TWbs+tPtUfLChNAjA@mail.gmail.com>
Date:   Fri, 9 Jun 2017 14:27:27 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] ipv4: igmp: fix a use after free

On Fri, Jun 9, 2017 at 2:05 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Thu, Jun 8, 2017 at 6:37 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> On Thu, 2017-06-08 at 17:59 -0700, Cong Wang wrote:
>>> On Thu, Jun 8, 2017 at 1:33 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>>> > I mentioned (in https://lkml.org/lkml/2017/5/31/619 ) that we might need
>>> > to defer freeing after rcu grace period but for some reason decided it
>>> > was not needed.
>>>
>>> This one makes sense, it is the second time I saw the use-after-free
>>> in igmp code, both are because we don't respect the RCU rule to free
>>> an element in the list.
>>>
>>> >
>>> > What about :
>>>
>>> But not sure if all ip_ma_put() callers want ip_mc_clear_src().
>>
>> That would lead to a memory leak if this was the case ?
>
> Maybe, but looking at igmpv3_clear_delrec() again, seems
> we can just acquire pmc->lock in ip_mc_clear_src() to serialize
> with the readers?
just refreshed the page and saw your reply, the same way as
I just replied