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Date:   Wed, 8 Jan 2020 17:34:21 -0800
From:   Song Liu <song@...nel.org>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [bpf PATCH 1/9] bpf: sockmap/tls, during free we may call
 tcp_bpf_unhash() in loop

On Wed, Jan 8, 2020 at 1:14 PM John Fastabend <john.fastabend@...il.com> wrote:
>
> When a sockmap is free'd and a socket in the map is enabled with tls
> we tear down the bpf context on the socket, the psock struct and state,
> and then call tcp_update_ulp(). The tcp_update_ulp() call is to inform
> the tls stack it needs to update its saved sock ops so that when the tls
> socket is later destroyed it doesn't try to call the now destroyed psock
> hooks.
>
> This is about keeping stacked ULPs in good shape so they always have
> the right set of stacked ops.
>
> However, recently unhash() hook was removed from TLS side. But, the
> sockmap/bpf side is not doing any extra work to update the unhash op
> when is torn down instead expecting TLS side to manage it. So both
> TLS and sockmap believe the other side is managing the op and instead
> no one updates the hook so it continues to point at tcp_bpf_unhash().
> When unhash hook is called we call tcp_bpf_unhash() which detects the
> psock has already been destroyed and calls sk->sk_prot_unhash() which
> calls tcp_bpf_unhash() yet again and so on looping and hanging the core.
>
> To fix have sockmap tear down logic fixup the stale pointer.
>
> Fixes: 5d92e631b8be ("net/tls: partially revert fix transition through disconnect with close")
> Reported-by: syzbot+83979935eb6304f8cd46@...kaller.appspotmail.com
> Signed-off-by: John Fastabend <john.fastabend@...il.com>

Cc: stable@...r.kernel.org
Acked-by: Song Liu <songliubraving@...com>

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