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Date:   Thu, 12 May 2022 13:09:23 -0700
From:   Eric Dumazet <>
To:     Leonard Crestez <>
Cc:     "David S. Miller" <>,
        David Ahern <>,
        netdev <>,
        LKML <>
Subject: Re: BUG: TCP timewait sockets survive across namespace creation in net-next

On Thu, May 12, 2022 at 11:13 AM Eric Dumazet <> wrote:
> On Thu, May 12, 2022 at 11:01 AM Leonard Crestez <> 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.

Oh well, too many changes would be needed.
I will send a revert, thanks.

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