Different return value from s2n_connection_get_client_protocol_version depending on security_policy configured

[raycoll]

Problem:

s2n_connection_get_client_protocol_version returns S2N_TLS12 when a client connects that supports TLS1.3 if the s2n_connection is configured with a TLS1.2 max security policy.

When a TLS1.3 max security policy is configured, s2n_connection_get_client_protocol_version returns S2N_TLS13 as expected.

Solution:

Ideally, s2n_connection_get_client_protocol_version should return the same value regardless of the server configuration used.

• Does this change what S2N sends over the wire? No
• Does this change any public APIs? Yes, to make the return value of s2n_connection_get_client_protocol_version consistent.
• Which versions of TLS will this impact?

Requirements / Acceptance Criteria:

I would expect s2n_connection_get_client_protocol_version to always return S2N_TLS13 when a client connects that supports TLS1.3.

[raycoll]

repros using s2nd/openssl s_client:

• s2nd reports S2N_TLS12 despite s_client enabling TLS1.3

> DYLD_LIBRARY_PATH=/opt/homebrew/Cellar/openssl@3/3.1.2/lib:/Volumes/workplace/s2n-tls/build/lib/lib ./build/bin/s2nd 0.0.0.0 10000
Listening on 0.0.0.0:10000
Client hello version: 33
Client protocol version: 33
Server protocol version: 33
Actual protocol version: 33
Curve: secp256r1
KEM: NONE
KEM Group: NONE
Cipher negotiated: ECDHE-RSA-AES128-GCM-SHA256
Server signature negotiated: RSA+SHA256


> openssl s_client -min_protocol 'TLSv1' -max_protocol 'TLSv1.3' 127.0.0.1:10000
...
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES128-GCM-SHA256
...

• s2nd reports S2N_TLS13 with the same client but using a 1.3 security policy:

> DYLD_LIBRARY_PATH=/opt/homebrew/Cellar/openssl@3/3.1.2/lib:/Volumes/workplace/s2n-tls/build/lib/lib ./build/bin/s2nd -c default_tls13 0.0.0.0 10000
Listening on 0.0.0.0:10000
the conn->client_protocol_version 34
the conn->client_protocol_version 34
CONNECTED:
Handshake: NEGOTIATED|FULL_HANDSHAKE|MIDDLEBOX_COMPAT
Client hello version: 33
Client protocol version: 34
Server protocol version: 34
Actual protocol version: 34
Curve: x25519
KEM: NONE
KEM Group: NONE
Cipher negotiated: TLS_AES_128_GCM_SHA256

>  openssl s_client -min_protocol 'TLSv1' -max_protocol 'TLSv1.3' 127.0.0.1:10000
...
SSL-Session:
    Protocol  : TLSv1.3
    Cipher    : TLS_AES_128_GCM_SHA256

[maddeleine]

Note that this specifically an issue when this API is called on the server-side. This behavior is likely due to the fact that we don't process the supported_versions extension if the server doesn't support TLS1.3.