openssl

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History

Benjamin Kaduk 2aaa0b146b Restore sensible "sess_accept" counter tracking Commit `9ef9088c15` switched the SSL/SSL_CTX statistics counters to using Thread-Sanitizer-friendly primitives. However, it erroneously converted an addition of -1 (for s->session_ctx->stats.sess_accept) to an addition of +1, since that is the only counter API provided by the internal tsan_assist.h header until the previous commit. This means that for each accepted (initial) connection, the session_ctx's counter would get doubly incremented, and the (switched) ctx's counter would also get incremented. Restore the counter decrement so that each accepted connection increments exactly one counter exactly once (in net effect). Reviewed-by: Paul Dale <paul.dale@oracle.com> (Merged from https://github.com/openssl/openssl/pull/7464)		2018-11-03 23:12:45 -05:00
..
extensions_clnt.c	Use the same min-max version range on the client consistently	2018-08-22 15:15:19 +01:00
extensions_cust.c
extensions_srvr.c	Send a NewSessionTicket after using an external PSK	2018-09-04 11:22:26 +01:00
extensions.c	Restore sensible "sess_accept" counter tracking	2018-11-03 23:12:45 -05:00
README
statem_clnt.c	Don't call the client_cert_cb immediately in TLSv1.3	2018-10-30 12:08:42 +00:00
statem_dtls.c	Don't memcpy the contents of an empty fragment	2018-05-12 09:59:02 +01:00
statem_lib.c	Don't call the client_cert_cb immediately in TLSv1.3	2018-10-30 12:08:42 +00:00
statem_locl.h
statem_srvr.c	Fix a DTLS memory leak	2018-10-19 14:12:51 +01:00
statem.c	Fix a possible recursion in SSLfatal handling	2018-09-12 14:43:13 +02:00
statem.h	Tolerate encrypted or plaintext alerts	2018-08-08 10:16:58 +01:00

README

State Machine Design
====================

This file provides some guidance on the thinking behind the design of the
state machine code to aid future maintenance.

The state machine code replaces an older state machine present in OpenSSL
versions 1.0.2 and below. The new state machine has the following objectives:
    - Remove duplication of state code between client and server
    - Remove duplication of state code between TLS and DTLS
    - Simplify transitions and bring the logic together in a single location
      so that it is easier to validate
    - Remove duplication of code between each of the message handling functions
    - Receive a message first and then work out whether that is a valid
      transition - not the other way around (the other way causes lots of issues
      where we are expecting one type of message next but actually get something
      else)
    - Separate message flow state from handshake state (in order to better
      understand each)
      - message flow state = when to flush buffers; handling restarts in the
        event of NBIO events; handling the common flow of steps for reading a
        message and the common flow of steps for writing a message etc
      - handshake state = what handshake message are we working on now
    - Control complexity: only the state machine can change state: keep all
      the state changes local to the state machine component

The message flow state machine is divided into a reading sub-state machine and a
writing sub-state machine. See the source comments in statem.c for a more
detailed description of the various states and transitions possible.

Conceptually the state machine component is designed as follows:

                        libssl
                           |
---------------------------|-----statem.h--------------------------------------
                           |
                    _______V____________________
                   |                            |
                   |    statem.c                |
                   |                            |
                   |    Core state machine code |
                   |____________________________|
        statem_locl.h     ^          ^
                 _________|          |_______
                |                            |
   _____________|____________   _____________|____________
  |                          | |                          |
  | statem_clnt.c            | | statem_srvr.c            |
  |                          | |                          |
  | TLS/DTLS client specific | | TLS/DTLS server specific |
  | state machine code       | | state machine code       |
  |__________________________| |__________________________|
               |        |_______________|__       |
               |        ________________|  |      |
               |       |                   |      |
   ____________V_______V________   ________V______V_______________
  |                             | |                               |
  | statem_both.c               | | statem_dtls.c                 |
  |                             | |                               |
  | Non core functions common   | | Non core functions common to  |
  | to both servers and clients | | both DTLS servers and clients |
  |_____________________________| |_______________________________|