gnutls: ensure TLS 1.3 when SRP isn't requested

When SRP is requested in the priority string, GnuTLS will disable
support for TLS 1.3. Before this change, curl would always add +SRP to
the priority list, effectively always disabling TLS 1.3 support.

With this change, +SRP is only added to the priority list when SRP
authentication is also requested. This also allows updating the error
handling here to not have to retry without SRP. This is because SRP is
only added when requested and in that case a retry is not needed.

Closes #5223

1 files changed, 45 insertions, 36 deletions

diff --git a/lib/vtls/gtls.c b/lib/vtls/gtls.c
index ec4904ee2..7192dd2e7 100644
--- a/lib/vtls/gtls.c
+++ b/lib/vtls/gtls.c
@@ -446,32 +446,32 @@ set_ssl_version_min_max(const char **prioritylist, struct connectdata *conn)
   switch(ssl_version | ssl_version_max) {
     case CURL_SSLVERSION_TLSv1_0 | CURL_SSLVERSION_MAX_TLSv1_0:
       *prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0:-VERS-TLS-ALL:"
-                      "+VERS-TLS1.0:" GNUTLS_SRP;
+                      "+VERS-TLS1.0";
       return CURLE_OK;
     case CURL_SSLVERSION_TLSv1_0 | CURL_SSLVERSION_MAX_TLSv1_1:
       *prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0:-VERS-TLS-ALL:"
-                      "+VERS-TLS1.0:+VERS-TLS1.1:" GNUTLS_SRP;
+                      "+VERS-TLS1.0:+VERS-TLS1.1";
       return CURLE_OK;
     case CURL_SSLVERSION_TLSv1_0 | CURL_SSLVERSION_MAX_TLSv1_2:
       *prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0:-VERS-TLS-ALL:"
-                      "+VERS-TLS1.0:+VERS-TLS1.1:+VERS-TLS1.2:" GNUTLS_SRP;
+                      "+VERS-TLS1.0:+VERS-TLS1.1:+VERS-TLS1.2";
       return CURLE_OK;
     case CURL_SSLVERSION_TLSv1_1 | CURL_SSLVERSION_MAX_TLSv1_1:
       *prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0:-VERS-TLS-ALL:"
-                      "+VERS-TLS1.1:" GNUTLS_SRP;
+                      "+VERS-TLS1.1";
       return CURLE_OK;
     case CURL_SSLVERSION_TLSv1_1 | CURL_SSLVERSION_MAX_TLSv1_2:
       *prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0:-VERS-TLS-ALL:"
-                      "+VERS-TLS1.1:+VERS-TLS1.2:" GNUTLS_SRP;
+                      "+VERS-TLS1.1:+VERS-TLS1.2";
       return CURLE_OK;
     case CURL_SSLVERSION_TLSv1_2 | CURL_SSLVERSION_MAX_TLSv1_2:
       *prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0:-VERS-TLS-ALL:"
-                      "+VERS-TLS1.2:" GNUTLS_SRP;
+                      "+VERS-TLS1.2";
       return CURLE_OK;
     case CURL_SSLVERSION_TLSv1_3 | CURL_SSLVERSION_MAX_TLSv1_3:
 #ifdef HAS_TLS13
        *prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0:-VERS-TLS-ALL:"
-                       "+VERS-TLS1.3:" GNUTLS_SRP;
+                       "+VERS-TLS1.3";
       return CURLE_OK;
 #else
        failf(data, "GnuTLS: TLS 1.3 is not yet supported");
@@ -479,35 +479,35 @@ set_ssl_version_min_max(const char **prioritylist, struct connectdata *conn)
 #endif
     case CURL_SSLVERSION_TLSv1_0 | CURL_SSLVERSION_MAX_DEFAULT:
       *prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0:-VERS-TLS-ALL:"
-                      "+VERS-TLS1.0:+VERS-TLS1.1:+VERS-TLS1.2:"
+                      "+VERS-TLS1.0:+VERS-TLS1.1:+VERS-TLS1.2"
 #ifdef HAS_TLS13
-                      "+VERS-TLS1.3:"
+                      ":+VERS-TLS1.3"
 #endif
-                      GNUTLS_SRP;
+                      ;
       return CURLE_OK;
     case CURL_SSLVERSION_TLSv1_1 | CURL_SSLVERSION_MAX_DEFAULT:
       *prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0:-VERS-TLS-ALL:"
-                      "+VERS-TLS1.1:+VERS-TLS1.2:"
+                      "+VERS-TLS1.1:+VERS-TLS1.2"
 #ifdef HAS_TLS13
-                      "+VERS-TLS1.3:"
+                      ":+VERS-TLS1.3"
 #endif
-                      GNUTLS_SRP;
+                      ;
       return CURLE_OK;
     case CURL_SSLVERSION_TLSv1_2 | CURL_SSLVERSION_MAX_DEFAULT:
       *prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0:-VERS-TLS-ALL:"
-                      "+VERS-TLS1.2:"
+                      "+VERS-TLS1.2"
 #ifdef HAS_TLS13
-                      "+VERS-TLS1.3:"
+                      ":+VERS-TLS1.3"
 #endif
-                      GNUTLS_SRP;
+                      ;
       return CURLE_OK;
     case CURL_SSLVERSION_TLSv1_3 | CURL_SSLVERSION_MAX_DEFAULT:
       *prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0:-VERS-TLS-ALL:"
-                      "+VERS-TLS1.2:"
+                      "+VERS-TLS1.2"
 #ifdef HAS_TLS13
-                      "+VERS-TLS1.3:"
+                      ":+VERS-TLS1.3"
 #endif
-                      GNUTLS_SRP;
+                      ;
       return CURLE_OK;
   }
 
@@ -764,11 +764,11 @@ gtls_connect_step1(struct connectdata *conn,
       break;
     case CURL_SSLVERSION_DEFAULT:
     case CURL_SSLVERSION_TLSv1:
-      prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0:"
+      prioritylist = GNUTLS_CIPHERS ":-VERS-SSL3.0"
 #ifdef HAS_TLS13
-                     "+VERS-TLS1.3:"
+                     ":+VERS-TLS1.3"
 #endif
-                     GNUTLS_SRP;
+                     ;
       break;
     case CURL_SSLVERSION_TLSv1_0:
     case CURL_SSLVERSION_TLSv1_1:
@@ -787,24 +787,33 @@ gtls_connect_step1(struct connectdata *conn,
       failf(data, "Unrecognized parameter passed via CURLOPT_SSLVERSION");
       return CURLE_SSL_CONNECT_ERROR;
   }
-  rc = gnutls_priority_set_direct(session, prioritylist, &err);
-  if((rc == GNUTLS_E_INVALID_REQUEST) && err) {
-    if(!strcmp(err, GNUTLS_SRP)) {
-      /* This GnuTLS was probably compiled without support for SRP.
-       * Note that fact and try again without it. */
-      int validprioritylen = curlx_uztosi(err - prioritylist);
-      char *prioritycopy = strdup(prioritylist);
-      if(!prioritycopy)
-        return CURLE_OUT_OF_MEMORY;
 
+#ifdef USE_TLS_SRP
+  /* Only add SRP to the cipher list if SRP is requested. Otherwise
+   * GnuTLS will disable TLS 1.3 support. */
+  if(SSL_SET_OPTION(authtype) == CURL_TLSAUTH_SRP) {
+    size_t len = strlen(prioritylist);
+
+    char *prioritysrp = malloc(len + sizeof(GNUTLS_SRP) + 1);
+    if(!prioritysrp)
+      return CURLE_OUT_OF_MEMORY;
+    strcpy(prioritysrp, prioritylist);
+    strcpy(prioritysrp + len, ":" GNUTLS_SRP);
+
+    rc = gnutls_priority_set_direct(session, prioritysrp, &err);
+    free(prioritysrp);
+
+    if((rc == GNUTLS_E_INVALID_REQUEST) && err) {
       infof(data, "This GnuTLS does not support SRP\n");
-      if(validprioritylen)
-        /* Remove the :+SRP */
-        prioritycopy[validprioritylen - 1] = 0;
-      rc = gnutls_priority_set_direct(session, prioritycopy, &err);
-      free(prioritycopy);
     }
   }
+  else {
+#endif
+    rc = gnutls_priority_set_direct(session, prioritylist, &err);
+#ifdef USE_TLS_SRP
+  }
+#endif
+
   if(rc != GNUTLS_E_SUCCESS) {
     failf(data, "Error %d setting GnuTLS cipher list starting with %s",
           rc, err);