.\"	$OpenBSD: SSL_SESSION_free.3,v 1.2 2016/12/06 18:53:55 schwarze Exp $
.\"	OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100
.\"
.\" This file was written by Lutz Jaenicke <jaenicke@openssl.org>.
.\" Copyright (c) 2000, 2001, 2009 The OpenSSL Project.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in
.\"    the documentation and/or other materials provided with the
.\"    distribution.
.\"
.\" 3. All advertising materials mentioning features or use of this
.\"    software must display the following acknowledgment:
.\"    "This product includes software developed by the OpenSSL Project
.\"    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
.\"
.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
.\"    endorse or promote products derived from this software without
.\"    prior written permission. For written permission, please contact
.\"    openssl-core@openssl.org.
.\"
.\" 5. Products derived from this software may not be called "OpenSSL"
.\"    nor may "OpenSSL" appear in their names without prior written
.\"    permission of the OpenSSL Project.
.\"
.\" 6. Redistributions of any form whatsoever must retain the following
.\"    acknowledgment:
.\"    "This product includes software developed by the OpenSSL Project
.\"    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
.\" OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: December 6 2016 $
.Dt SSL_SESSION_FREE 3
.Os
.Sh NAME
.Nm SSL_SESSION_free
.Nd free an allocated SSL_SESSION structure
.Sh SYNOPSIS
.In openssl/ssl.h
.Ft void
.Fn SSL_SESSION_free "SSL_SESSION *session"
.Sh DESCRIPTION
.Fn SSL_SESSION_free
decrements the reference count of
.Fa session
and removes the
.Vt SSL_SESSION
structure pointed to by
.Fa session
and frees up the allocated memory, if the reference count has reached 0.
If
.Fa session
is a
.Dv NULL
pointer, no action occurs.
.Pp
.Vt SSL_SESSION
objects are allocated when a TLS/SSL handshake operation is successfully
completed.
Depending on the settings, see
.Xr SSL_CTX_set_session_cache_mode 3 ,
the
.Vt SSL_SESSION
objects are internally referenced by the
.Vt SSL_CTX
and linked into its session cache.
.Vt SSL
objects may be using the
.Vt SSL_SESSION
object; as a session may be reused, several
.Vt SSL
objects may be using one
.Vt SSL_SESSION
object at the same time.
It is therefore crucial to keep the reference count (usage information) correct
and not delete a
.Vt SSL_SESSION
object that is still used, as this may lead to program failures due to dangling
pointers.
These failures may also appear delayed, e.g., when an
.Vt SSL_SESSION
object is completely freed as the reference count incorrectly becomes 0, but it
is still referenced in the internal session cache and the cache list is
processed during a
.Xr SSL_CTX_flush_sessions 3
operation.
.Pp
.Fn SSL_SESSION_free
must only be called for
.Vt SSL_SESSION
objects, for which the reference count was explicitly incremented (e.g., by
calling
.Xr SSL_get1_session 3 ;
see
.Xr SSL_get_session 3 )
or when the
.Vt SSL_SESSION
object was generated outside a TLS handshake operation, e.g., by using
.Xr d2i_SSL_SESSION 3 .
It must not be called on other
.Vt SSL_SESSION
objects, as this would cause incorrect reference counts and therefore program
failures.
.Sh SEE ALSO
.Xr d2i_SSL_SESSION 3 ,
.Xr SSL_CTX_flush_sessions 3 ,
.Xr SSL_CTX_set_session_cache_mode 3 ,
.Xr SSL_get_session 3 ,
.Xr SSL_SESSION_new 3