netdev - Re: [PATCH v1 net] tcp: Clean up kernel listener's reqsk in inet_twsk

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Date:   Thu, 13 Oct 2022 08:56:50 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Kuniyuki Iwashima <kuniyu@...zon.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH v1 net] tcp: Clean up kernel listener's reqsk in inet_twsk_purge()

On Wed, Oct 12, 2022 at 7:51 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> Eric Dumazet reported a use-after-free related to the per-netns ehash
> series. [0]
>
> When we create a TCP socket from userspace, the socket always holds a
> refcnt of the netns.  This guarantees that a reqsk timer is always fired
> before netns dismantle.  Each reqsk has a refcnt of its listener, so the
> listener is not freed before the reqsk, and the net is not freed before
> the listener as well.
>
...

> Fixes: d1e5e6408b30 ("tcp: Introduce optional per-netns ehash.")
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Reported-by: Eric Dumazet <edumazet@...gle.com>
> Suggested-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
Reviewed-by: Eric Dumazet <edumazet@...gle.com>