Implement using --peer-fingerprint without CA certificates

This is implements --peer-fingerprint command to support OpenVPN
authentication without involving a PKI.

The current implementation in OpenVPN for peer fingerprint has been already
extensively rewritten from the original submission from Jason [1]. The
commit preserved the original author since it was based on Jason code/idea.

This commit is based on two previous commits that prepare the infrastructure
to use a simple to use --peer-fingerprint directive instead of using
a --tls-verify script like the v1 of the patch proposed.  The two commits
preparing this are:

 - Extend verify-hash to allow multiple hashes
 - Implement peer-fingerprint to check fingerprint of peer certificate

These preceding patches make this actual patch quite short. There are some
lines in this patch that bear some similarity to the ones like

    if (!preverify_ok && !session->opt->verify_hash_no_ca)

vs

    if (!preverify_ok && !session->opt->ca_file_none)

But these similarities are one line fragments and dictated by the
surrounding style and program flow, so even a complete black box
implementation will likely end up with the same lines.

[1] https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg16781.html

Change-Id: Ie74c3d606c5429455c293c367462244566a936e3
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20230524132424.3098475-2-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26723.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index 008bae982b4b65991dd9b607514232b635ff54b8..6fb6900de67fde89de149ed8865ef7f057e83bb4 100644 (file)
--- a/src/openvpn/init.c
+++ b/src/openvpn/init.c
@@ -3345,6 +3345,7 @@ do_init_crypto_tls(struct context *c, const unsigned int flags)
     to.verify_hash = options->verify_hash;
     to.verify_hash_algo = options->verify_hash_algo;
     to.verify_hash_depth = options->verify_hash_depth;
+    to.verify_hash_no_ca = options->verify_hash_no_ca;
 #ifdef ENABLE_X509ALTUSERNAME
     memcpy(to.x509_username_field, options->x509_username_field, sizeof(to.x509_username_field));
 #else

diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 3a6990e77c6d710082613ee911026280c0455ddc..90d85be426c40452c2287fa8a2f9d0f2d6b28936 100644 (file)
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -2987,21 +2987,11 @@ options_postprocess_verify_ce(const struct options *options,
         else
         {
 #ifdef ENABLE_CRYPTO_MBEDTLS
-            if (!(options->ca_file))
-            {
-                msg(M_USAGE, "You must define CA file (--ca)");
-            }
-
             if (options->ca_path)
             {
                 msg(M_USAGE, "Parameter --capath cannot be used with the mbed TLS version version of OpenVPN.");
             }
-#else  /* ifdef ENABLE_CRYPTO_MBEDTLS */
-            if ((!(options->ca_file)) && (!(options->ca_path)))
-            {
-                msg(M_USAGE, "You must define CA file (--ca) or CA path (--capath)");
-            }
-#endif
+#endif  /* ifdef ENABLE_CRYPTO_MBEDTLS */
             if (pull)
             {
 
@@ -3733,6 +3723,13 @@ options_postprocess_mutate(struct options *o, struct env_set *es)
         options_postprocess_http_proxy_override(o);
     }
 #endif
+    if (!o->ca_file && !o->ca_path && o->verify_hash
+        && o->verify_hash_depth == 0)
+    {
+        msg(M_INFO, "Using certificate fingerprint to verify peer (no CA "
+            "option set). ");
+        o->verify_hash_no_ca = true;
+    }
 
     if (o->config && streq(o->config, "stdin") && o->remap_sigusr1 == SIGHUP)
     {
@@ -4028,8 +4025,11 @@ options_postprocess_filechecks(struct options *options)
     errs |= check_file_access_inline(options->dh_file_inline, CHKACC_FILE,
                                      options->dh_file, R_OK, "--dh");
 
-    errs |= check_file_access_inline(options->ca_file_inline, CHKACC_FILE,
-                                     options->ca_file, R_OK, "--ca");
+    if (!options->verify_hash_no_ca)
+    {
+        errs |= check_file_access_inline(options->ca_file_inline, CHKACC_FILE,
+                                         options->ca_file, R_OK, "--ca");
+    }
 
     errs |= check_file_access_chroot(options->chroot_dir, CHKACC_FILE,
                                      options->ca_path, R_OK, "--capath");

diff --git a/src/openvpn/options.h b/src/openvpn/options.h
index 95f1158a4e32623ccfdab81ced0d9b377bb00df4..f5890b90ffb352f2a9126e6d6fa221bcc21d9fee 100644 (file)
--- a/src/openvpn/options.h
+++ b/src/openvpn/options.h
@@ -604,6 +604,7 @@ struct options
     struct verify_hash_list *verify_hash;
     hash_algo_type verify_hash_algo;
     int verify_hash_depth;
+    bool verify_hash_no_ca;
     unsigned int ssl_flags; /* set to SSLF_x flags from ssl.h */
 
 #ifdef ENABLE_PKCS11

diff --git a/src/openvpn/ssl_common.h b/src/openvpn/ssl_common.h
index c0b3caa71019f7ab5f65edf1423dd42f9692e389..27b02947993e9a0b325c36980ee3dd87ce26d5ca 100644 (file)
--- a/src/openvpn/ssl_common.h
+++ b/src/openvpn/ssl_common.h
@@ -345,6 +345,7 @@ struct tls_options
     const char *remote_cert_eku;
     struct verify_hash_list *verify_hash;
     int verify_hash_depth;
+    bool verify_hash_no_ca;
     hash_algo_type verify_hash_algo;
 #ifdef ENABLE_X509ALTUSERNAME
     char *x509_username_field[MAX_PARMS];

diff --git a/src/openvpn/ssl_verify_mbedtls.c b/src/openvpn/ssl_verify_mbedtls.c
index 2a205c8a437b4a96d2aafa15116642cd8733292b..a1ddf8d0bd9e7910d774f81c439247cfad82cf1f 100644 (file)
--- a/src/openvpn/ssl_verify_mbedtls.c
+++ b/src/openvpn/ssl_verify_mbedtls.c
@@ -60,6 +60,22 @@ verify_callback(void *session_obj, mbedtls_x509_crt *cert, int cert_depth,
     struct buffer cert_fingerprint = x509_get_sha256_fingerprint(cert, &gc);
     cert_hash_remember(session, cert_depth, &cert_fingerprint);
 
+    if (session->opt->verify_hash_no_ca)
+    {
+        /*
+         * If we decide to verify the peer certificate based on the fingerprint
+         * we ignore wrong dates and the certificate not being trusted.
+         * Any other problem with the certificate (wrong key, bad cert,...)
+         * will still trigger an error.
+         * Clearing these flags relies on verify_cert will later rejecting a
+         * certificate that has no matching fingerprint.
+         */
+        uint32_t flags_ignore = MBEDTLS_X509_BADCERT_NOT_TRUSTED
+                                | MBEDTLS_X509_BADCERT_EXPIRED
+                                | MBEDTLS_X509_BADCERT_FUTURE;
+        *flags = *flags & ~flags_ignore;
+    }
+
     /* did peer present cert which was signed by our root cert? */
     if (*flags != 0)
     {

diff --git a/src/openvpn/ssl_verify_openssl.c b/src/openvpn/ssl_verify_openssl.c
index 177200aaa53a55edfba724d07f3b1402abbc2815..3194c232a74f7b276d5dadcc25211beaa1e27c0d 100644 (file)
--- a/src/openvpn/ssl_verify_openssl.c
+++ b/src/openvpn/ssl_verify_openssl.c
@@ -65,7 +65,7 @@ verify_callback(int preverify_ok, X509_STORE_CTX *ctx)
     cert_hash_remember(session, X509_STORE_CTX_get_error_depth(ctx), &cert_hash);
 
     /* did peer present cert which was signed by our root cert? */
-    if (!preverify_ok)
+    if (!preverify_ok && !session->opt->verify_hash_no_ca)
     {
         /* get the X509 name */
         char *subject = x509_get_subject(current_cert, &gc);