netdev - Re: [PATCH RFC 4/5] net/tls: Add support for PF

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Date:   Mon, 25 Apr 2022 10:14:59 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Chuck Lever <chuck.lever@...cle.com>
Cc:     netdev@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-cifs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, ak@...pesta-tech.com,
        borisp@...dia.com, simo@...hat.com
Subject: Re: [PATCH RFC 4/5] net/tls: Add support for PF_TLSH (a TLS
 handshake listener)

On Mon, 18 Apr 2022 12:49:50 -0400 Chuck Lever wrote:
> In-kernel TLS consumers need a way to perform a TLS handshake. In
> the absence of a handshake implementation in the kernel itself, a
> mechanism to perform the handshake in user space, using an existing
> TLS handshake library, is necessary.
> 
> I've designed a way to pass a connected kernel socket endpoint to
> user space using the traditional listen/accept mechanism. accept(2)
> gives us a well-understood way to materialize a socket endpoint as a
> normal file descriptor in a specific user space process. Like any
> open socket descriptor, the accepted FD can then be passed to a
> library such as openSSL to perform a TLS handshake.
> 
> This prototype currently handles only initiating client-side TLS
> handshakes. Server-side handshakes and key renegotiation are left
> to do.
> 
> Security Considerations
> ~~~~~~~~ ~~~~~~~~~~~~~~
> 
> This prototype is net-namespace aware.
> 
> The kernel has no mechanism to attest that the listening user space
> agent is trustworthy.
> 
> Currently the prototype does not handle multiple listeners that
> overlap -- multiple listeners in the same net namespace that have
> overlapping bind addresses.

Create the socket in user space, do all the handshakes you need there
and then pass it to the kernel.  This is how NBD + TLS works.  Scales
better and requires much less kernel code.