328fd88333
As was done for ciphers, supported groups, and EC point formats in https://github.com/openssl/openssl/pull/9162, only write the negotiated SNI hostname value to the session object when not resuming, even for TLS 1.3 resumptions. Otherwise, when using a stateful session cache (as is done by default when 0-RTT data is enabled), we can have multiple SSLs active using the same in-memory session object, which leads to double-frees and similar race conditions in the SNI handler prior to this commit. Fortunately, since draft-ietf-tls-tls13-22, there is no requirement that the SNI hostname be preserved across TLS 1.3 resumption, and thus not a need to continually update the session object with the "current" value (to be used when producing session tickets, so that the subsequent resumption can be checked against the current value). So we can just relax the logic and only write to the session object for initial handshakes. This still leaves us in a somewhat inconsistent state, since if the SNI value does change across handshakes, the session object will continue to record the initial handshake's value, even if that bears no relation to the current handshake. The current SSL_get_servername() implementation prefers the value from the session if s->hit, but a more complete fix for that and related issues is underway in https://github.com/openssl/openssl/pull/10018; there is no need to wait for the complete fix for SNI name handling in order to close the race condition and avoid runtime crashes. Reviewed-by: Matt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/10441) (cherry picked from commit 2a5385511051d33be8d2b20d7669d8b1862fe510) |
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|---|---|---|
| .. | ||
| extensions.c | ||
| extensions_clnt.c | ||
| extensions_cust.c | ||
| extensions_srvr.c | ||
| README | ||
| statem.c | ||
| statem.h | ||
| statem_clnt.c | ||
| statem_dtls.c | ||
| statem_lib.c | ||
| statem_local.h | ||
| statem_srvr.c | ||
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_local.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 |
|_____________________________| |_______________________________|