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If s->hit is set, s->session corresponds to a session created on a previous connection, and is a data structure that is potentially shared across other SSL objects. As such, there are thread-safety issues with modifying the structure without taking its lock (and of course all corresponding read accesses would also need to take the lock as well), which have been observed to cause double-frees. Regardless of thread-safety, the resumed session object is intended to reflect parameters of the connection that created the session, and modifying it to reflect the parameters from the current connection is confusing. So, modifications to the session object during ClientHello processing should only be performed on new connections, i.e., those where s->hit is not set. The code mostly got this right, providing such checks when processing SNI and EC point formats, but the supported groups (formerly supported curves) extension was missing it, which is fixed by this commit. However, TLS 1.3 makes the suppported_groups extension mandatory (when using (EC)DHE, which is the normal case), checking for the group list in the key_share extension processing. But, TLS 1.3 only [0] supports session tickets for session resumption, so the session object in question is the output of d2i_SSL_SESSION(), and will not be shared across SSL objects. Thus, it is safe to modify s->session for TLS 1.3 connections. [0] A psk_find_session callback can also be used, but the restriction that each callback execution must produce a distinct SSL_SESSION structure can be documented when the psk_find_session callback documentation is completed. Reviewed-by: Andy Polyakov <appro@openssl.org> (Merged from https://github.com/openssl/openssl/pull/4123) |
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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_locl.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_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 | |_____________________________| |_______________________________|