netdev - Re: [PATCH] netfilter: nf_tables: always synchronize with readers before releasing tables

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Message-ID: <ee004a9d-7d49-448f-16d7-807afc755dd0@virtuozzo.com>
Date:   Tue, 28 Feb 2023 11:54:51 +0200
From:   Alexander Atanasov <alexander.atanasov@...tuozzo.com>
To:     Florian Westphal <fw@...len.de>
Cc:     netdev@...r.kernel.org, Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH] netfilter: nf_tables: always synchronize with readers
 before releasing tables

On 28.02.23 1:31, Florian Westphal wrote:
> Alexander Atanasov <alexander.atanasov@...tuozzo.com> wrote:
>> As i said i am still trying to figure out the basechain place,
>> where is that synchronize_rcu() call done?
> 
> cleanup_net() in net/core/net_namespace.c.
> 
> pre_exit handlers run, then synchronize_rcu, then the
> normal exit handlers, then exit_batch.

It prevents anyone new to find the namespace but it does not guard 
against the ones that have already found it.
What stops them to enter a rcu_read_lock() section after the synchronize 
call in cleanup_net() is done and race with the exit handler?

synchronize_rcu() must be called with the commit_mutex held to be safe 
against lock less readers using data protected with commit_mutext.

-- 
Regards,
Alexander Atanasov