From: Arne Schwabe <arne@rfc2549.org>
Date: Fri, 22 Nov 2019 14:33:14 +0000 (+0100)
Subject: Make tls_version_max return the actual maximum version
X-Git-Tag: v2.5_beta1~235
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6328aef94a748bd9859ae5cd264b7e50fbb8a325;p=thirdparty%2Fopenvpn.git

Make tls_version_max return the actual maximum version

Before OpenSSL 1.1.1 there could be no mismatch between
compiled and actual OpenSSL version. With OpenSSL 1.1.1 we need
runtime detection to detect the actual best TLS version supported.

Allowing this runtime detection also allows removing some of the
TLS 1.3/OpenSSL 1.1.1 #ifdefs

Without this patch tls-min-version 1.3 or-highest will actually
downgrade to TLS 1.2 in the "compiled with 1.1.0 and linked against
1.1.1" scenario.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Selva Nair <selva.nair@gmail.com>
Message-Id: <20191122143315.8564-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg19186.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
---

diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
index 4455ebb89..e708fc939 100644
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -4194,12 +4194,11 @@ show_available_tls_ciphers(const char *cipher_list,
 {
     printf("Available TLS Ciphers, listed in order of preference:\n");
 
-#if (ENABLE_CRYPTO_OPENSSL && OPENSSL_VERSION_NUMBER >= 0x1010100fL)
-    printf("\nFor TLS 1.3 and newer (--tls-ciphersuites):\n\n");
-    show_available_tls_ciphers_list(cipher_list_tls13, tls_cert_profile, true);
-#else
-    (void) cipher_list_tls13;  /* Avoid unused warning */
-#endif
+    if (tls_version_max() >= TLS_VER_1_3)
+    {
+        printf("\nFor TLS 1.3 and newer (--tls-ciphersuites):\n\n");
+        show_available_tls_ciphers_list(cipher_list_tls13, tls_cert_profile, true);
+    }
 
     printf("\nFor TLS 1.2 and older (--tls-cipher):\n\n");
     show_available_tls_ciphers_list(cipher_list, tls_cert_profile, false);
diff --git a/src/openvpn/ssl_openssl.c b/src/openvpn/ssl_openssl.c
index 07916c3c8..a080338e2 100644
--- a/src/openvpn/ssl_openssl.c
+++ b/src/openvpn/ssl_openssl.c
@@ -215,7 +215,26 @@ int
 tls_version_max(void)
 {
 #if defined(TLS1_3_VERSION)
+    /* If this is defined we can safely assume TLS 1.3 support */
     return TLS_VER_1_3;
+#elif OPENSSL_VERSION_NUMBER >= 0x10100000L
+    /*
+     * If TLS_VER_1_3 is not defined, we were compiled against a version that
+     * did not support TLS 1.3.
+     *
+     * However, the library we are *linked* against might be OpenSSL 1.1.1
+     * and therefore supports TLS 1.3. This needs to be checked at runtime
+     * since we can be compiled against 1.1.0 and then the library can be
+     * upgraded to 1.1.1
+     */
+    if (OpenSSL_version_num() >= 0x1010100fL)
+    {
+        return TLS_VER_1_3;
+    }
+    else
+    {
+        return TLS_VER_1_2;
+    }
 #elif defined(TLS1_2_VERSION) || defined(SSL_OP_NO_TLSv1_2)
     return TLS_VER_1_2;
 #elif defined(TLS1_1_VERSION) || defined(SSL_OP_NO_TLSv1_1)
@@ -241,12 +260,25 @@ openssl_tls_version(int ver)
     {
         return TLS1_2_VERSION;
     }
-#if defined(TLS1_3_VERSION)
     else if (ver == TLS_VER_1_3)
     {
+        /*
+         * Supporting the library upgraded to TLS1.3 without recompile
+         * is enough to support here with a simple constant that the same
+         * as in the TLS 1.3, so spec it is very unlikely that OpenSSL
+         * will change this constant
+         */
+#ifndef TLS1_3_VERSION
+        /*
+         * We do not want to define TLS_VER_1_3 if not defined
+         * since other parts of the code use the existance of this macro
+         * as proxy for TLS 1.3 support
+         */
+        return 0x0304;
+#else
         return TLS1_3_VERSION;
-    }
 #endif
+    }
     return 0;
 }
 
@@ -2015,7 +2047,8 @@ show_available_tls_ciphers_list(const char *cipher_list,
 #if defined(TLS1_3_VERSION)
     if (tls13)
     {
-        SSL_CTX_set_min_proto_version(tls_ctx.ctx, TLS1_3_VERSION);
+        SSL_CTX_set_min_proto_version(tls_ctx.ctx,
+                                      openssl_tls_version(TLS_VER_1_3));
         tls_ctx_restrict_ciphers_tls13(&tls_ctx, cipher_list);
     }
     else