netdev - Re: [PATCH net v2] ip6mr: fix stale iterator

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Date:   Wed, 31 Jan 2018 16:11:07 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Cc:     netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        syzkaller-bugs@...glegroups.com,
        bot+eceb3204562c41a438fa1f2335e0fe4f6886d669@...kaller.appspotmail.com,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        roopa@...ulusnetworks.com, Eric Biggers <ebiggers3@...il.com>
Subject: Re: [PATCH net v2] ip6mr: fix stale iterator

On Wed, Jan 31, 2018 at 3:52 PM, Nikolay Aleksandrov
<nikolay@...ulusnetworks.com> wrote:
> On 31/01/18 16:49, Dmitry Vyukov wrote:
>> On Wed, Jan 31, 2018 at 3:29 PM, Nikolay Aleksandrov
>> <nikolay@...ulusnetworks.com> wrote:
>>> When we dump the ip6mr mfc entries via proc, we initialize an iterator
>>> with the table to dump but we don't clear the cache pointer which might
>>> be initialized from a prior read on the same descriptor that ended. This
>>> can result in lock imbalance (an unnecessary unlock) leading to other
>>> crashes and hangs. Clear the cache pointer like ipmr does to fix the issue.
>>> Thanks for the reliable reproducer.
> [snip]
>>> Reported-by: syzbot <bot+eceb3204562c41a438fa1f2335e0fe4f6886d669@...kaller.appspotmail.com>
>>> Signed-off-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
>>> ---
>>> v2: make sure the trace doesn't ruin the patch
>>> No fixes tag because it seems this has been there forever.
>>
>> Don't we need to Cc stable 2.6 in this case or something like this. We
>> want it to be backported.
>
> AFAIK Dave takes care of queueing the patches for stable backports and
> maintainers get them from his stable queue.

Good to know. Thanks.

>>>  net/ipv6/ip6mr.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
>>> index a2e1a864eb46..4fc566ec7e79 100644
>>> --- a/net/ipv6/ip6mr.c
>>> +++ b/net/ipv6/ip6mr.c
>>> @@ -495,6 +495,7 @@ static void *ipmr_mfc_seq_start(struct seq_file *seq, loff_t *pos)
>>>                 return ERR_PTR(-ENOENT);
>>>
>>>         it->mrt = mrt;
>>> +       it->cache = NULL;
>>>         return *pos ? ipmr_mfc_seq_idx(net, seq->private, *pos - 1)
>>>                 : SEQ_START_TOKEN;
>>>  }
>>> --
>>> 2.1.4
>>>
>>> --
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>