s2n_connection_set_session shouldn't mutate on failure

[lrstewart]

Problem:

When calling s2n_connection_set_session with a TLS1.2 ticket, we copy values like cipher suite and the master secret from the ticket to the connection: https://github.com/aws/s2n-tls/blob/main/tls/s2n_resume.c#L236-L252 This means that we mutate the connection even if s2n_connection_set_session fails.

There's a more minor version of the problem for TLS1.3, where on a failure we won't clear conn->client_ticket like we should: https://github.com/aws/s2n-tls/blob/main/tls/s2n_resume.c#L355C1-L361

Solution:

Rewrite the deserialization so that the connection isn't affected unless we actually successfully deserialize the ticket.

• Does this change what S2N sends over the wire? If yes, explain.
• Does this change any public APIs? If yes, explain.
• Which versions of TLS will this impact?

Requirements / Acceptance Criteria:

What must a solution address in order to solve the problem? How do we know the solution is complete?

• RFC links: Links to relevant RFC(s)
• Related Issues: Link any relevant issues
• Will the Usage Guide or other documentation need to be updated?
• Testing: How will this change be tested? Call out new integration tests, functional tests, or particularly interesting/important unit tests.
  • Will this change trigger SAW changes? Changes to the state machine, the s2n_handshake_io code that controls state transitions, the DRBG, or the corking/uncorking logic could trigger SAW failures.
  • Should this change be fuzz tested? Will it handle untrusted input? Create a separate issue to track the fuzzing work.

Out of scope:

Is there anything the solution will intentionally NOT address?