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

[Chuck Lever III]

Hi Jakub-

> On Apr 25, 2022, at 1:14 PM, Jakub Kicinski <kuba at kernel.org> wrote:
> 
> 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.

The RPC-with-TLS standard allows unencrypted RPC traffic on the connection
before sending ClientHello. I think we'd like to stick with creating the
socket in the kernel, for this reason and for the reasons Hannes mentions
in his reply.

--
Chuck Lever