netdev - Re: [Patch net] xt_RATEEST: acquire xt_rateest

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Date:   Thu, 1 Feb 2018 13:50:40 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        netfilter-devel@...r.kernel.org,
        Pablo Neira Ayuso <pablo@...filter.org>
Subject: Re: [Patch net] xt_RATEEST: acquire xt_rateest_mutex for hash insert

On Wed, Jan 31, 2018 at 5:44 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Wed, 2018-01-31 at 16:26 -0800, Cong Wang wrote:
>> rateest_hash is supposed to be protected by xt_rateest_mutex.
>>
>> Reported-by: <syzbot+5cb189720978275e4c75@...kaller.appspotmail.com>
>> Fixes: 5859034d7eb8 ("[NETFILTER]: x_tables: add RATEEST target")
>> Cc: Pablo Neira Ayuso <pablo@...filter.org>
>> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
>> ---
>>  net/netfilter/xt_RATEEST.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/net/netfilter/xt_RATEEST.c b/net/netfilter/xt_RATEEST.c
>> index 498b54fd04d7..83ec3a282755 100644
>> --- a/net/netfilter/xt_RATEEST.c
>> +++ b/net/netfilter/xt_RATEEST.c
>> @@ -36,7 +36,9 @@ static void xt_rateest_hash_insert(struct xt_rateest *est)
>>       unsigned int h;
>>
>>       h = xt_rateest_hash(est->name);
>> +     mutex_lock(&xt_rateest_mutex);
>>       hlist_add_head(&est->list, &rateest_hash[h]);
>> +     mutex_unlock(&xt_rateest_mutex);
>>  }
>
> We probably should make this module netns aware, otherwise bad things
> will happen.

Right, both the lock and the hashtable. I can do it for net-next,
if you don't.

>
> (It seems multiple threads could run, so getting the mutex twice
> (xt_rateest_lookup then xt_rateest_hash_insert() is racy)

Yeah, need to merge these two critical sections.

Thanks.