Update the SSL_dup documentation to match reality

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/12245)

1 files changed, 72 insertions, 4 deletions

diff --git a/doc/man3/SSL_new.pod b/doc/man3/SSL_new.pod
index 222e9d5886..ac4b7a46cd 100644
--- a/doc/man3/SSL_new.pod
+++ b/doc/man3/SSL_new.pod
@@ -26,10 +26,78 @@ structure are freed.
 SSL_up_ref() increments the reference count for an
 existing B<SSL> structure.
 
-SSL_dup() duplicates an existing B<SSL> structure into a new allocated one. All
-settings are inherited from the original B<SSL> structure. Dynamic data (i.e.
-existing connection details) are not copied, the new B<SSL> is set into an
-initial accept (server) or connect (client) state.
+The function SSL_dup() creates and returns a new B<SSL> structure from the same
+B<SSL_CTX> that was used to create I<s>. It additionally duplicates a subset of
+the settings in I<s> into the new B<SSL> object.
+
+For SSL_dup() to work, the connection MUST be in its initial state and
+MUST NOT have not yet have started the SSL handshake.  For connections
+that are not in their initial state SSL_dup() just increments an internal
+reference count and returns the I<same> handle.  It may be possible to
+use L<SSL_clear(3)> to recycle an SSL handle that is not in its initial
+state for re-use, but this is best avoided.  Instead, save and restore
+the session, if desired, and construct a fresh handle for each connection.
+
+The subset of settings in I<s> that are duplicated are:
+
+=over 4
+
+=item any session data if configured (including the session_id_context)
+
+=item any tmp_dh settings set via L<SSL_set_tmp_dh(3)>,
+L<SSL_set_tmp_dh_callback(3)>, or L<SSL_set_dh_auto(3)>
+
+=item any configured certificates, private keys or certificate chains
+
+=item any configured signature algorithms, or client signature algorithms
+
+=item any DANE settings
+
+=item any Options set via L<SSL_set_options(3)>
+
+=item any Mode set via L<SSL_set_mode(3)>
+
+=item any minimum or maximum protocol settings set via
+L<SSL_set_min_proto_version(3)> or L<SSL_set_max_proto_version(3)> (Note: Only
+from OpenSSL 1.1.1h and above)
+
+=item any Verify mode, callback or depth set via L<SSL_set_verify(3)> or
+L<SSL_set_verify_depth(3)> or any configured X509 verification parameters
+
+=item any msg callback or info callback set via L<SSL_set_msg_callback(3)> or
+L<SSL_set_info_callback(3)>
+
+=item any default password callback set via L<SSL_set_default_passwd_cb(3)>
+
+=item any session id generation callback set via L<SSL_set_generate_session_id(3)>
+
+=item any configured Cipher List
+
+=item any BIOs configured on I<s> will have new BIO's created and the BIO state
+duplicated via BIO_dup_state().
+
+=item initial accept (server) or connect (client) state
+
+=item the max cert list value set via L<SSL_set_max_cert_list(3)>
+
+=item the read_ahead value set via L<SSL_set_read_ahead(3)>
+
+=item application specific data set via L<SSL_set_ex_data(3)>
+
+=item any CA list or client CA list set via L<SSL_set0_CA_list(3)>,
+SSL_set0_client_CA_list() or similar functions
+
+=item any security level settings or callbacks
+
+=item any configured serverinfo data
+
+=item any configured PSK identity hint
+
+=item any configured custom extensions
+
+=item any client certificate types configured via SSL_set1_client_certificate_types
+
+=back
 
 =head1 RETURN VALUES