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c8e2f98c97
This partially reverts commit c636c1c47. It also tweaks the documentation and comments in this area. On the client side the documented interface for SSL_CTX_set_verify()/SSL_set_verify() is that setting the flag SSL_VERIFY_PEER causes verfication of the server certificate to take place. Previously what was implemented was that if *any* flag was set then verification would take place. The above commit improved the semantics to be as per the documented interface. However, we have had a report of at least one application where an application was incorrectly using the interface and used *only* SSL_VERIFY_FAIL_IF_NO_PEER_CERT on the client side. In OpenSSL prior to the above commit this still caused verification of the server certificate to take place. After this commit the application silently failed to verify the server certificate. Ideally SSL_CTX_set_verify()/SSL_set_verify() could be modified to indicate if invalid flags were being used. However these are void functions! The simplest short term solution is to revert to the previous behaviour which at least means we "fail closed" rather than "fail open". Thanks to Cory Benfield for reporting this issue. Reviewed-by: Richard Levitte <levitte@openssl.org>
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 |
|_____________________________| |_______________________________|