netdev - Re: [PATCH 2/3] tcp: Add ESP encapsulation support

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Date:   Tue, 16 Jan 2018 11:28:23 +0100
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
CC:     Herbert Xu <herbert@...dor.apana.org.au>, <netdev@...r.kernel.org>
Subject: Re: [PATCH 2/3] tcp: Add ESP encapsulation support

On Fri, Jan 12, 2018 at 08:38:01AM -0800, Eric Dumazet wrote:
> On Fri, 2018-01-12 at 00:21 +1100, Herbert Xu wrote:
> > This patch adds the plumbing in TCP for ESP encapsulation support
> > per RFC8229.
> > 
> > The patch mostly deals with inbound processing, as well as enabling
> > TCP encapsulation on a socket through setsockopt.  The outbound
> > processing is dealt with in the ESP code as is done for UDP.
> > 
> > The inbound processing is split into two halves.  First of all,
> > the softirq path directly intercepts ESP packets and feeds them
> > into the IPsec stack.  Most of the time the packet will be freed
> > right away if it contains complete ESP packets.  However, if
> > the message is incomplete or it contains non-ESP data, then the
> > skb will be added to the receive queue.  We also add packets to
> > the receive queue if it is currently non-emtpy, in order to
> > preserve sequence number continuity and minimise the changes
> > to the TCP code.
> > 
> > On the user-space facing side, packets marked as ESP-only are
> > skipped and not visible to user-space.  However, some ESP data
> > may seep through.  For example, if we receive a partial message
> > then we will always give it to user-space regardless of whether
> > it turns out to be ESP or not.  So user-space should be prepared
> > to skip ESP messages (SPI != 0).
> > 
> > There is a little bit of code dealing with the encapsulation side.
> > In particular, if encapsulation data comes in while the socket
> > is owned by user-space, the packets will be stored in tp->encap_out
> > and processed during release_sock.
> > 
> > Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
> > ---
> > 
> >  include/linux/tcp.h      |   15 ++
> >  include/net/tcp.h        |   27 +++
> >  include/uapi/linux/tcp.h |    1 
> >  include/uapi/linux/udp.h |    1 
> >  net/ipv4/tcp.c           |   68 +++++++++
> >  net/ipv4/tcp_input.c     |  326 +++++++++++++++++++++++++++++++++++++++++++++--
> >  net/ipv4/tcp_ipv4.c      |    1 
> >  net/ipv4/tcp_output.c    |   48 ++++++
> >  8 files changed, 473 insertions(+), 14 deletions(-)
> > 
> 
> Ouch...
> 
> Is there any chance this can be done with almost no change in TCP
> stack, using a layer model ? ( net/kcm comes to mind )

Herbert, would this be an option or is this not possible?

Thanks!