netdev - Re: [bpf PATCH v2 6/6] bpf: sockmap/tls, close can race with map free

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Date:   Thu, 11 Jul 2019 09:39:53 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        John Fastabend <john.fastabend@...il.com>
Cc:     ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org,
        edumazet@...gle.com, bpf@...r.kernel.org
Subject: Re: [bpf PATCH v2 6/6] bpf: sockmap/tls, close can race with map free

Jakub Kicinski wrote:
> On Tue, 09 Jul 2019 20:33:58 -0700, John Fastabend wrote:
> > Jakub Kicinski wrote:
> > > On Mon, 08 Jul 2019 19:15:18 +0000, John Fastabend wrote:  
> > > > @@ -352,15 +354,18 @@ static void tls_sk_proto_close(struct sock *sk, long timeout)
> > > >  	if (ctx->tx_conf == TLS_BASE && ctx->rx_conf == TLS_BASE)
> > > >  		goto skip_tx_cleanup;
> > > >  
> > > > -	sk->sk_prot = ctx->sk_proto;
> > > >  	tls_sk_proto_cleanup(sk, ctx, timeo);
> > > >  
> > > >  skip_tx_cleanup:
> > > > +	write_lock_bh(&sk->sk_callback_lock);
> > > > +	icsk->icsk_ulp_data = NULL;  
> > > 
> > > Is ulp_data pointer now supposed to be updated under the
> > > sk_callback_lock?  
> > 
> > Yes otherwise it can race with tls_update(). I didn't remove the
> > ulp pointer null set from tcp_ulp.c though. Could be done in this
> > patch or as a follow up.
> 
> Do we need to hold the lock in unhash, too, or is unhash called with
> sk_callback_lock held?
> 

We should hold the lock here. Also we should reset sk_prot similar to
other paths in case we get here without a close() call. syzbot hasn't
found that path yet but I'll add some tests for it.

	write_lock_bh(...)
	icsk_ulp_data = NULL
	sk->sk_prot = ctx->sk_proto;
	write_unlock_bh(...)

Thanks