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

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Message-ID: <CAM_iQpUd0uO63zPzC6ijYRcRAZSrW_C_trWA5vyRM_9OsHLU-A@mail.gmail.com>
Date:   Thu, 8 Jun 2017 23:05:10 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Xin Long <lucien.xin@...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 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?