Replace handling of negative verification result with SSL_set_retry_verify()
Provide a different mechanism to indicate that the application wants
to retry the verification. The negative result of the callback function
now indicates an error again.
Instead the SSL_set_retry_verify() can be called from the callback
to indicate that the handshake should be suspended.
Fixes #17568
Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17825)
diff --git a/doc/man3/SSL_set_retry_verify.pod b/doc/man3/SSL_set_retry_verify.pod
new file mode 100644
index 0000000..4eb7f44
--- /dev/null
+++ b/doc/man3/SSL_set_retry_verify.pod
@@ -0,0 +1,70 @@
+=pod
+
+=head1 NAME
+
+SSL_set_retry_verify - indicate that certificate verification should be retried
+
+=head1 SYNOPSIS
+
+ #include <openssl/ssl.h>
+
+ int SSL_set_retry_verify(SSL *ssl);
+
+=head1 DESCRIPTION
+
+SSL_set_retry_verify() should be called from the certificate verification
+callback on a client when the application wants to indicate that the handshake
+should be suspended and the control should be returned to the application.
+L<SSL_want_retry_verify(3)> will return 1 as a consequence until the handshake
+is resumed again by the application, retrying the verification step.
+
+Please refer to L<SSL_CTX_set_cert_verify_callback(3)> for further details.
+
+=head1 NOTES
+
+The effect of calling SSL_set_retry_verify() outside of the certificate
+verification callback on the client side is undefined.
+
+=head1 RETURN VALUES
+
+SSL_set_retry verify() returns 1 on success, 0 otherwise.
+
+=head1 EXAMPLES
+
+The following code snippet shows how to obtain the B<SSL> object associated
+with the B<X509_STORE_CTX> to call the SSL_set_retry_verify() function:
+
+ int idx = SSL_get_ex_data_X509_STORE_CTX_idx();
+ SSL *ssl;
+
+ /* this should not happen but check anyway */
+ if (idx < 0
+ || (ssl = X509_STORE_CTX_get_ex_data(ctx, idx)) == NULL)
+ return 0;
+
+ if (/* we need to retry verification callback */)
+ return SSL_set_retry_verify(ssl);
+
+ /* do normal processing of the verification callback */
+
+=head1 SEE ALSO
+
+L<ssl(7)>, L<SSL_connect(3)>, L<SSL_CTX_set_cert_verify_callback(3)>,
+L<SSL_want_retry_verify(3)>
+
+=head1 HISTORY
+
+SSL_set_retry_verify() was added in OpenSSL 3.0.2 to replace backwards
+incompatible handling of a negative return value from the verification
+callback.
+
+=head1 COPYRIGHT
+
+Copyright 2022 The OpenSSL Project Authors. All Rights Reserved.
+
+Licensed under the Apache License 2.0 (the "License"). You may not use
+this file except in compliance with the License. You can obtain a copy
+in the file LICENSE in the source distribution or at
+L<https://www.openssl.org/source/license.html>.
+
+=cut
