NAME

SSL_SESSION_up_ref, SSL_SESSION_free — SSL_SESSION reference counting

SYNOPSIS

#include <openssl/ssl.h> int
SSL_SESSION_up_ref(SSL_SESSION *session); void
SSL_SESSION_free(SSL_SESSION *session);

DESCRIPTION

SSL_SESSION_up_ref() increments the reference count of the given session by 1. SSL_SESSION_free() decrements the reference count of the given session by 1. If the reference count reaches 0, it frees the memory used by the session. If session is a NULL pointer, no action occurs. SSL_SESSION objects are allocated when a TLS/SSL handshake operation is successfully completed. Depending on the settings, see SSL_CTX_set_session_cache_mode(3), the SSL_SESSION objects are internally referenced by the SSL_CTX and linked into its session cache. SSL objects may be using the SSL_SESSION object; as a session may be reused, several SSL objects may be using one SSL_SESSION object at the same time. It is therefore crucial to keep the reference count (usage information) correct and not delete a 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 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 SSL_CTX_flush_sessions(3) operation. SSL_SESSION_free() must only be called for SSL_SESSION objects, for which the reference count was explicitly incremented (e.g., by calling SSL_get1_session(3); see SSL_get_session(3)) or when the SSL_SESSION object was generated outside a TLS handshake operation, e.g., by using d2i_SSL_SESSION(3). It must not be called on other SSL_SESSION objects, as this would cause incorrect reference counts and therefore program failures.

RETURN VALUES

SSL_SESSION_up_ref() returns 1 on success or 0 on error.

SEE ALSO

d2i_SSL_SESSION(3), ssl(3), SSL_CTX_flush_sessions(3), SSL_CTX_set_session_cache_mode(3), SSL_get_session(3), SSL_SESSION_new(3)

HISTORY

SSL_SESSION_free() first appeared in SSLeay 0.5.2 and has been available since OpenBSD 2.4. SSL_SESSION_up_ref() first appeared in OpenSSL 1.1.0 and has been available since OpenBSD 6.3.