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188d4ec82a
The existing documentation for the new-session callback was unclear about the requirements on the callback with respect to reference-handling of the session object being created. Be more explicit about the (non-)requirements on the callback code for "success" (1) and "ignore" (0) return values. Reviewed-by: Matt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/10848)
121 lines
5.6 KiB
Plaintext
121 lines
5.6 KiB
Plaintext
=pod
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=head1 NAME
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SSL_CTX_sess_set_new_cb, SSL_CTX_sess_set_remove_cb, SSL_CTX_sess_set_get_cb, SSL_CTX_sess_get_new_cb, SSL_CTX_sess_get_remove_cb, SSL_CTX_sess_get_get_cb - provide callback functions for server side external session caching
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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void SSL_CTX_sess_set_new_cb(SSL_CTX *ctx,
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int (*new_session_cb)(SSL *, SSL_SESSION *));
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void SSL_CTX_sess_set_remove_cb(SSL_CTX *ctx,
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void (*remove_session_cb)(SSL_CTX *ctx,
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SSL_SESSION *));
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void SSL_CTX_sess_set_get_cb(SSL_CTX *ctx,
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SSL_SESSION (*get_session_cb)(SSL *,
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const unsigned char *,
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int, int *));
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int (*SSL_CTX_sess_get_new_cb(SSL_CTX *ctx))(struct ssl_st *ssl,
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SSL_SESSION *sess);
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void (*SSL_CTX_sess_get_remove_cb(SSL_CTX *ctx))(struct ssl_ctx_st *ctx,
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SSL_SESSION *sess);
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SSL_SESSION *(*SSL_CTX_sess_get_get_cb(SSL_CTX *ctx))(struct ssl_st *ssl,
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const unsigned char *data,
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int len, int *copy);
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=head1 DESCRIPTION
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SSL_CTX_sess_set_new_cb() sets the callback function, which is automatically
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called whenever a new session was negotiated.
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SSL_CTX_sess_set_remove_cb() sets the callback function, which is
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automatically called whenever a session is removed by the SSL engine,
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because it is considered faulty or the session has become obsolete because
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of exceeding the timeout value.
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SSL_CTX_sess_set_get_cb() sets the callback function which is called,
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whenever a SSL/TLS client proposed to resume a session but the session
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could not be found in the internal session cache (see
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L<SSL_CTX_set_session_cache_mode(3)>).
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(SSL/TLS server only.)
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SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb(), and
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SSL_CTX_sess_get_get_cb() retrieve the function pointers set by the
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corresponding set callback functions. If a callback function has not been
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set, the NULL pointer is returned.
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=head1 NOTES
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In order to allow external session caching, synchronization with the internal
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session cache is realized via callback functions. Inside these callback
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functions, session can be saved to disk or put into a database using the
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L<d2i_SSL_SESSION(3)> interface.
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The new_session_cb() is called whenever a new session has been negotiated and
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session caching is enabled (see L<SSL_CTX_set_session_cache_mode(3)>). The
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new_session_cb() is passed the B<ssl> connection and the ssl session B<sess>.
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Since sessions are reference-counted objects, the reference count on the
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session is incremented before the callback, on behalf of the application. If
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the callback returns B<0>, the session will be immediately removed from the
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internal cache and the reference count released. If the callback returns B<1>,
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the application retains the reference (for an entry in the
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application-maintained "external session cache"), and is responsible for
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calling SSL_SESSION_free() when the session reference is no longer in use.
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Note that in TLSv1.3, sessions are established after the main
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handshake has completed. The server decides when to send the client the session
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information and this may occur some time after the end of the handshake (or not
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at all). This means that applications should expect the new_session_cb()
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function to be invoked during the handshake (for <= TLSv1.2) or after the
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handshake (for TLSv1.3). It is also possible in TLSv1.3 for multiple sessions to
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be established with a single connection. In these case the new_session_cb()
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function will be invoked multiple times.
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In TLSv1.3 it is recommended that each SSL_SESSION object is only used for
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resumption once. One way of enforcing that is for applications to call
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L<SSL_CTX_remove_session(3)> after a session has been used.
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The remove_session_cb() is called, whenever the SSL engine removes a session
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from the internal cache. This happens when the session is removed because
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it is expired or when a connection was not shutdown cleanly. It also happens
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for all sessions in the internal session cache when
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L<SSL_CTX_free(3)> is called. The remove_session_cb() is passed
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the B<ctx> and the ssl session B<sess>. It does not provide any feedback.
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The get_session_cb() is only called on SSL/TLS servers with the session id
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proposed by the client. The get_session_cb() is always called, also when
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session caching was disabled. The get_session_cb() is passed the
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B<ssl> connection, the session id of length B<length> at the memory location
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B<data>. With the parameter B<copy> the callback can require the
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SSL engine to increment the reference count of the SSL_SESSION object,
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Normally the reference count is not incremented and therefore the
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session must not be explicitly freed with
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L<SSL_SESSION_free(3)>.
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=head1 RETURN VALUES
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SSL_CTX_sess_get_new_cb(), SSL_CTX_sess_get_remove_cb() and SSL_CTX_sess_get_get_cb()
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return different callback function pointers respectively.
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=head1 SEE ALSO
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L<ssl(7)>, L<d2i_SSL_SESSION(3)>,
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L<SSL_CTX_set_session_cache_mode(3)>,
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L<SSL_CTX_flush_sessions(3)>,
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L<SSL_SESSION_free(3)>,
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L<SSL_CTX_free(3)>
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=head1 COPYRIGHT
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Copyright 2001-2018 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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