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From:   Eric Dumazet <edumazet@google.com>
Date:   Thu, 12 May 2022 11:13:46 -0700
Message-ID: <CANn89iKjt1wpGk1dqqnYYx3r9UzEc3rwNtvBQ1O2dVToY_7rBQ@mail.gmail.com>
Subject: Re: BUG: TCP timewait sockets survive across namespace creation in net-next
To:     Leonard Crestez <cdleonard@gmail.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        David Ahern <dsahern@kernel.org>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, May 12, 2022 at 11:01 AM Leonard Crestez <cdleonard@gmail.com> wrote:
>
> Hello,
>
> It appears that in recent net-next versions it is possible for sockets
> in the timewait state to survive across namespace add/del. Timewait
> sockets are inserted into a global hash and only the sock_net value is
> compared when they are enumerated from interfaces like /proc/net/tcp and
> inet_diag. Old TW sockets are not cleared after namespace delete and
> namespaces are allocated from a slab and thus their pointers get reused
> a lot, when that happens timewait sockets from an old namespace will
> show up in the new one.
>
> This can be reproduced by establishing a TCP connection over a veth pair
> between two namespaces, closing and then recreating those namespaces.
> Old timewait sockets will be visible and it happens quite reliably,
> often on the first iteration. I can try to provide a script for this.
>
> I can't point to specific bugs outside of tests that explicitly
> enumerate timewait sockets but letting sk_net be a dangling pointer
> seems very dangerous. It also violates the idea of network namespaces
> being independent and isolated.
>
> This does not happen in 5.17, I bisected this behavior to commit
> 0dad4087a86a ("tcp/dccp: get rid of inet_twsk_purge()")
>

Thanks for the report.

I guess we will need to store the (struct net)->net_cookie to
disambiguate the case
where a new 'struct net' is reusing the same storage than an old one.