linux-kernel - Re: general protection fault in tls_write

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Date:   Tue, 13 Aug 2019 11:59:48 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+dcdc9deefaec44785f32@...kaller.appspotmail.com>,
        aviadye@...lanox.com, borisp@...lanox.com, daniel@...earbox.net,
        davejwatson@...com, davem@...emloft.net,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        oss-drivers@...ronome.com, syzkaller-bugs@...glegroups.com,
        willemb@...gle.com
Subject: Re: general protection fault in tls_write_space

On Tue, 13 Aug 2019 11:30:00 -0700, John Fastabend wrote:
> Jakub Kicinski wrote:
> > On Tue, 13 Aug 2019 10:17:06 -0700, John Fastabend wrote:  
> > > > Followup of commit 95fa145479fb
> > > > ("bpf: sockmap/tls, close can race with map free")
> > > > 
> > > > --- a/net/tls/tls_main.c
> > > > +++ b/net/tls/tls_main.c
> > > > @@ -308,6 +308,9 @@ static void tls_sk_proto_close(struct so
> > > >  	if (free_ctx)
> > > >  		icsk->icsk_ulp_data = NULL;
> > > >  	sk->sk_prot = ctx->sk_proto;
> > > > +	/* tls will go; restore sock callback before enabling bh */
> > > > +	if (sk->sk_write_space == tls_write_space)
> > > > +		sk->sk_write_space = ctx->sk_write_space;
> > > >  	write_unlock_bh(&sk->sk_callback_lock);
> > > >  	release_sock(sk);
> > > >  	if (ctx->tx_conf == TLS_SW)    
> > > 
> > > Hi Hillf,
> > > 
> > > We need this patch (although slightly updated for bpf tree) do
> > > you want to send it? Otherwise I can. We should only set this if
> > > TX path was enabled otherwise we null it. Checking against
> > > tls_write_space seems best to me as well.
> > > 
> > > Against bpf this patch should fix it.
> > > 
> > > diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
> > > index ce6ef56a65ef..43252a801c3f 100644
> > > --- a/net/tls/tls_main.c
> > > +++ b/net/tls/tls_main.c
> > > @@ -308,7 +308,8 @@ static void tls_sk_proto_close(struct sock *sk, long timeout)
> > >         if (free_ctx)
> > >                 icsk->icsk_ulp_data = NULL;
> > >         sk->sk_prot = ctx->sk_proto;
> > > -       sk->sk_write_space = ctx->sk_write_space;
> > > +       if (sk->sk_write_space == tls_write_space)
> > > +               sk->sk_write_space = ctx->sk_write_space;
> > >         write_unlock_bh(&sk->sk_callback_lock);
> > >         release_sock(sk);
> > >         if (ctx->tx_conf == TLS_SW)  
> > 
> > This is already in net since Friday:  
> 
> Don't we need to guard that with an
> 
>   if (sk->sk_write_space == tls_write_space)
> 
> or something similar? Where is ctx->sk_write_space set in the rx only
> case? In do_tls_setsockop_conf() we have this block
> 
> 	if (tx) {
> 		ctx->sk_write_space = sk->sk_write_space;
> 		sk->sk_write_space = tls_write_space;
> 	} else {
> 		sk->sk_socket->ops = &tls_sw_proto_ops;
> 	}
> 
> which makes me think ctx->sk_write_space may not be set correctly in
> all cases.

Ah damn, you're right I remember looking at that but then I went down
the rabbit hole of trying to repro and forgot :/

Do you want to send an incremental change?