Re: [PATCH RFC 4/5] net/tls: Add support for PF_TLSH (a TLS handshake listener)

Jakub Kicinski
2022-04-25T17:18:20Z

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.