netdev - Re: [bpf PATCH v2 1/8] bpf: sockmap/tls, during free we may call tcp_bpf

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Date:   Mon, 13 Jan 2020 19:19:52 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Jakub Sitnicki <jakub@...udflare.com>,
        John Fastabend <john.fastabend@...il.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, daniel@...earbox.net,
        ast@...nel.org, song@...nel.org, jonathan.lemon@...il.com
Subject: Re: [bpf PATCH v2 1/8] bpf: sockmap/tls, during free we may call
 tcp_bpf_unhash() in loop

Jakub Sitnicki wrote:
> On Sat, Jan 11, 2020 at 07:11 AM CET, John Fastabend 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
> > Cc: stable@...r.kernel.org
> > Acked-by: Song Liu <songliubraving@...com>
> > Signed-off-by: John Fastabend <john.fastabend@...il.com>
> > ---
> >  include/linux/skmsg.h | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
> > index ef7031f8a304..b6afe01f8592 100644
> > --- a/include/linux/skmsg.h
> > +++ b/include/linux/skmsg.h
> > @@ -358,6 +358,7 @@ static inline void sk_psock_update_proto(struct sock *sk,
> >  static inline void sk_psock_restore_proto(struct sock *sk,
> >  					  struct sk_psock *psock)
> >  {
> > +	sk->sk_prot->unhash = psock->saved_unhash;
> 
> We could also restore it from psock->sk_proto->unhash if we were not
> NULL'ing on first call, right?
> 
> I've been wondering what is the purpose of having psock->saved_unhash
> and psock->saved_close if we have the whole sk->sk_prot saved in
> psock->sk_proto.

Its historical we can do some cleanups in net-next to simplify this a bit.
I don't think it needs to be done in bpf tree though.

> 
> >  	sk->sk_write_space = psock->saved_write_space;
> >
> >  	if (psock->sk_proto) {
> 
> Reviewed-by: Jakub Sitnicki <jakub@...udflare.com>