netdev - Re: [oss-drivers] Re: [PATCH net-next] net/tls: prevent skb_orphan() from leaking TLS plain text with offload

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Message-ID: <CAF=yD-+1jUkwXxyOyiH6qwheLTDNQupS_qg+Ra4WbtSogXp4nQ@mail.gmail.com>
Date:   Wed, 31 Jul 2019 15:07:39 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     David Miller <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        oss-drivers@...ronome.com, Eric Dumazet <edumazet@...gle.com>,
        borisp@...lanox.com, aviadye@...lanox.com, davejwatson@...com,
        John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Florian Westphal <fw@...len.de>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [oss-drivers] Re: [PATCH net-next] net/tls: prevent skb_orphan()
 from leaking TLS plain text with offload

On Wed, Jul 31, 2019 at 2:12 PM Jakub Kicinski
<jakub.kicinski@...ronome.com> wrote:
>
> On Wed, 31 Jul 2019 11:57:10 -0400, Willem de Bruijn wrote:
> > On Tue, Jul 30, 2019 at 5:13 PM Jakub Kicinski wrote:
> > > sk_validate_xmit_skb() and drivers depend on the sk member of
> > > struct sk_buff to identify segments requiring encryption.
> > > Any operation which removes or does not preserve the original TLS
> > > socket such as skb_orphan() or skb_clone() will cause clear text
> > > leaks.
> > >
> > > Make the TCP socket underlying an offloaded TLS connection
> > > mark all skbs as decrypted, if TLS TX is in offload mode.
> > > Then in sk_validate_xmit_skb() catch skbs which have no socket
> > > (or a socket with no validation) and decrypted flag set.
> > >
> > > Note that CONFIG_SOCK_VALIDATE_XMIT, CONFIG_TLS_DEVICE and
> > > sk->sk_validate_xmit_skb are slightly interchangeable right now,
> > > they all imply TLS offload. The new checks are guarded by
> > > CONFIG_TLS_DEVICE because that's the option guarding the
> > > sk_buff->decrypted member.
> > >
> > > Second, smaller issue with orphaning is that it breaks
> > > the guarantee that packets will be delivered to device
> > > queues in-order. All TLS offload drivers depend on that
> > > scheduling property. This means skb_orphan_partial()'s
> > > trick of preserving partial socket references will cause
> > > issues in the drivers. We need a full orphan, and as a
> > > result netem delay/throttling will cause all TLS offload
> > > skbs to be dropped.
> > >
> > > Reusing the sk_buff->decrypted flag also protects from
> > > leaking clear text when incoming, decrypted skb is redirected
> > > (e.g. by TC).
> > >
> > > Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
>
> > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > index d57b0cc995a0..b0c10b518e65 100644
> > > --- a/net/core/sock.c
> > > +++ b/net/core/sock.c
> > > @@ -1992,6 +1992,22 @@ void skb_set_owner_w(struct sk_buff *skb, struct sock *sk)
> > >  }
> > >  EXPORT_SYMBOL(skb_set_owner_w);
> > >
> > > +static bool can_skb_orphan_partial(const struct sk_buff *skb)
> > > +{
> > > +#ifdef CONFIG_TLS_DEVICE
> > > +       /* Drivers depend on in-order delivery for crypto offload,
> > > +        * partial orphan breaks out-of-order-OK logic.
> > > +        */
> > > +       if (skb->decrypted)
> > > +               return false;
> > > +#endif
> > > +#ifdef CONFIG_INET
> > > +       if (skb->destructor == tcp_wfree)
> > > +               return true;
> > > +#endif
> > > +       return skb->destructor == sock_wfree;
> > > +}
> > > +
> >
> > Just insert the skb->decrypted check into skb_orphan_partial for less
> > code churn?
>
> Okie.. skb_orphan_partial() is a little ugly but will do.
>
> > I also think that this is an independent concern from leaking plain
> > text, so perhaps could be a separate patch.

Just a suggestion and very much depending on how much uglier it
becomes otherwise ;)

> Do you mean the out-of-order stuff is a separate concern?
>
> It is, I had them separate at the first try, but GSO code looks at
> the destructor and IIRC only copies the socket if its still tcp_wfree.
> If we let partial orphan be we have to do temporary hairy stuff in
> tcp_gso_segment(). It's easier to just deal with partial orphan here.

Okay, sounds good.