From 0c3eb2793b2a1fe35beeb90ba8f5cb2a0fdc3270 Mon Sep 17 00:00:00 2001 From: "Dr. David von Oheimb" Date: Sat, 16 Jan 2021 20:43:00 +0100 Subject: TLS client: allow cert verify callback return -1 for SSL_ERROR_WANT_RETRY_VERIFY The client-side cert verification callback function may not only return as usual for success or 0 for failure, but also -1, typically on failure verifying the server certificate. This makes the handshake suspend and return control to the calling application with SSL_ERROR_WANT_RETRY_VERIFY. The app can for instance fetch further certificates or cert status information needed for the verification. Calling SSL_connect() again resumes the connection attempt by retrying the server certificate verification step. This process may even be repeated if need be. The core implementation of the feature is in ssl/statem/statem_clnt.c, splitting tls_process_server_certificate() into a preparation step that just copies the certificates received from the server to s->session->peer_chain (rather than having them in a local variable at first) and returns to the state machine, and a post-processing step in tls_post_process_server_certificate() that can be repeated: Try verifying the current contents of s->session->peer_chain basically as before, but give the verification callback function the chance to pause connecting and make the TLS state machine later call tls_post_process_server_certificate() again. Otherwise processing continues as usual. The documentation of the new feature is added to SSL_CTX_set_cert_verify_callback.pod and SSL_want.pod. This adds two tests: * A generic test in test/helpers/handshake.c on the usability of the new server cert verification retry feature. It is triggered via test/ssl-tests/03-custom_verify.cnf.in (while the bulky auto- generated changes to test/ssl-tests/03-custom_verify.cnf can be basically ignored). * A test in test/sslapitest.c that demonstrates the effectiveness of the approach for augmenting the cert chain provided by the server in between SSL_connect() calls. Reviewed-by: Matt Caswell (Merged from https://github.com/openssl/openssl/pull/13906) --- ssl/ssl_lib.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'ssl/ssl_lib.c') diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c index a8a1416073..c345a6b405 100644 --- a/ssl/ssl_lib.c +++ b/ssl/ssl_lib.c @@ -3808,6 +3808,8 @@ int SSL_get_error(const SSL *s, int i) } if (SSL_want_x509_lookup(s)) return SSL_ERROR_WANT_X509_LOOKUP; + if (SSL_want_retry_verify(s)) + return SSL_ERROR_WANT_RETRY_VERIFY; if (SSL_want_async(s)) return SSL_ERROR_WANT_ASYNC; if (SSL_want_async_job(s)) -- cgit v1.2.3