linux-kernel - Re: net/ipv4: use-after-free in add

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Date:   Thu, 1 Jun 2017 14:01:17 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "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>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/ipv4: use-after-free in add_grec

On Thu, Jun 1, 2017 at 2:13 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Wed, 2017-05-31 at 16:55 -0700, Eric Dumazet wrote:
>
>> The issue here is the timer firing while ip_mc_clear_src() has been
>> already called.
>>
>> My patch should fix the problem.
>>
>> Or another one using del_timer_sync() instead of del_timer() in
>> igmp_stop_timer(), but such a change would be more invasive,
>> since the del_timer_sync() would need to happen while im->lock
>> spinlock is not held.
>
> BTW, I guess that Andrey could try to add a delay to trigger the bug
> more often.

Applied, now testing with your patch.

Thanks!

>
> diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
> index 44fd86de2823dd17de16276a8ec01b190e69b8b4..84fff17daab0832c470a613b29b2aaade07cec0a 100644
> --- a/net/ipv4/igmp.c
> +++ b/net/ipv4/igmp.c
> @@ -798,7 +798,7 @@ static void igmp_timer_expire(unsigned long data)
>         }
>         im->reporter = 1;
>         spin_unlock(&im->lock);
> -
> +       udelay(10000);
>         if (IGMP_V1_SEEN(in_dev))
>                 igmp_send_report(in_dev, im, IGMP_HOST_MEMBERSHIP_REPORT);
>         else if (IGMP_V2_SEEN(in_dev))
>
>
> --
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