Improved dane_verify_session_crt(), which now attempts to create a full chain.

This addresses points from https://savannah.gnu.org/support/index.php?108552

diff --git a/libdane/dane.c b/libdane/dane.c
index edc8acfaaecaece909d3dc0928db0f30c0825e16..44734257bc275ed6e12f9c28a6a0abf262843efb 100644 (file)
--- a/libdane/dane.c
+++ b/libdane/dane.c
@@ -37,7 +37,7 @@
 #include "../lib/gnutls_int.h"
 
 #define MAX_DATA_ENTRIES 100
-
+#define DEBUG
 #ifdef DEBUG
 #define gnutls_assert() fprintf(stderr, "ASSERT: %s: %d\n", __FILE__, __LINE__);
 #define gnutls_assert_val(x) gnutls_assert_val_int(x, __FILE__, __LINE__)
@@ -734,7 +734,8 @@ dane_verify_crt_raw(dane_state_t s,
  * record then the verify flag %DANE_VERIFY_NO_DNSSEC_DATA is set.
  *
  * Note that the CA constraint only applies for the directly certifying CA
- * and does not account for long CA chains.
+ * and does not account for long CA chains. Moreover this function does not
+ * validate the provided chain.
  *
  * Due to the many possible options of DANE, there is no single threat
  * model countered. When notifying the user about DANE verification results
@@ -799,6 +800,10 @@ dane_verify_crt(dane_state_t s,
  * CA constrains and/or the certificate available via DANE.
  * See dane_verify_crt() for more information.
  *
+ * This will not verify the chain for validity; unless the DANE
+ * verification is restricted to end certificates, this has to
+ * be performed separately using gnutls_certificate_verify_peers3().
+ *
  * Returns: On success, %DANE_E_SUCCESS (0) is returned, otherwise a
  *   negative error value.
  *
@@ -813,6 +818,7 @@ dane_verify_session_crt(dane_state_t s,
        const gnutls_datum_t *cert_list;
        unsigned int cert_list_size = 0;
        unsigned int type;
+       int ret;
 
        cert_list = gnutls_certificate_get_peers(session, &cert_list_size);
        if (cert_list_size == 0) {
@@ -821,6 +827,69 @@ dane_verify_session_crt(dane_state_t s,
 
        type = gnutls_certificate_type_get(session);
 
+       /* this list may be incomplete, try to get the self-signed CA if any */
+       if (cert_list_size > 0) {
+               gnutls_datum_t new_cert_list[cert_list_size+1];
+               gnutls_x509_crt_t crt, ca;
+               gnutls_certificate_credentials_t sc;
+
+               ret = gnutls_x509_crt_init(&crt);
+               if (ret < 0) {
+                       gnutls_assert();
+                       goto failsafe;
+               }
+
+               ret = gnutls_x509_crt_import(crt, &cert_list[cert_list_size-1], GNUTLS_X509_FMT_DER);
+               if (ret < 0) {
+                       gnutls_assert();
+                       gnutls_x509_crt_deinit(crt);
+                       goto failsafe;
+               }
+
+               /* if it is already self signed continue normally */
+               ret = gnutls_x509_crt_check_issuer(crt, crt);
+               if (ret != 0) {
+                       gnutls_assert();
+                       gnutls_x509_crt_deinit(crt);
+                       goto failsafe;
+               }
+
+               /* chain does not finish in a self signed cert, try to obtain the issuer */
+               ret = gnutls_credentials_get(session, GNUTLS_CRD_CERTIFICATE, (void**)&sc);
+               if (ret < 0) {
+                       gnutls_assert();
+                       gnutls_x509_crt_deinit(crt);
+                       goto failsafe;
+               }
+
+               ret = gnutls_certificate_get_issuer(sc, crt, &ca, 0);
+               if (ret < 0) {
+                       gnutls_assert();
+                       gnutls_x509_crt_deinit(crt);
+                       goto failsafe;
+               }
+
+               /* make the new list */
+               memcpy(new_cert_list, cert_list, cert_list_size*sizeof(gnutls_datum_t));
+
+               ret = gnutls_x509_crt_export2(ca, GNUTLS_X509_FMT_DER, &new_cert_list[cert_list_size]);
+               if (ret < 0) {
+                       gnutls_assert();
+                       gnutls_x509_crt_deinit(crt);
+                       goto failsafe;
+               }
+
+               ret = dane_verify_crt(s, new_cert_list, cert_list_size+1, type,
+                              hostname, proto, port, sflags, vflags,
+                              verify);
+               if (ret < 0) {
+                       gnutls_assert();
+               }
+               gnutls_free(new_cert_list[cert_list_size].data);
+               return ret;
+       }
+
+ failsafe:
        return dane_verify_crt(s, cert_list, cert_list_size, type,
                               hostname, proto, port, sflags, vflags,
                               verify);