Skip to trusted certs early in the chain

This helps in the case where an intermediate certificate is directly trusted.
In that case we want to ignore what comes after it in the chain, not only for
performance but also to avoid false negatives (eg an old root being no longer
trusted while the newer intermediate is directly trusted).

closes #220

library/x509_crt.c

@@ -2062,8 +2062,8 @@ static int x509_crt_verify_child(
     *flags |= x509_crt_verifycrl(child, parent, ca_crl, profile );
 #endif
 
-    /* Look for a grandparent upwards the chain */
+    /* Look for a grandparent in trusted CAs */
-    for( grandparent = parent->next;
+    for( grandparent = trust_ca;
          grandparent != NULL;
          grandparent = grandparent->next )
     {
@@ -2072,20 +2072,42 @@ static int x509_crt_verify_child(
             break;
     }
 
-    /* Is our parent part of the chain or at the top? */
     if( grandparent != NULL )
     {
-        ret = x509_crt_verify_child( parent, grandparent, trust_ca, ca_crl, profile,
+        ret = x509_crt_verify_top( parent, grandparent, ca_crl, profile,
                                 path_cnt + 1, &parent_flags, f_vrfy, p_vrfy );
         if( ret != 0 )
             return( ret );
     }
     else
     {
-        ret = x509_crt_verify_top( parent, trust_ca, ca_crl, profile,
+        /* Look for a grandparent upwards the chain */
-                                path_cnt + 1, &parent_flags, f_vrfy, p_vrfy );
+        for( grandparent = parent->next;
-        if( ret != 0 )
+             grandparent != NULL;
-            return( ret );
+             grandparent = grandparent->next )
+        {
+            if( x509_crt_check_parent( parent, grandparent,
+                                       0, path_cnt == 0 ) == 0 )
+                break;
+        }
+
+        /* Is our parent part of the chain or at the top? */
+        if( grandparent != NULL )
+        {
+            ret = x509_crt_verify_child( parent, grandparent, trust_ca, ca_crl,
+                                         profile, path_cnt + 1, &parent_flags,
+                                         f_vrfy, p_vrfy );
+            if( ret != 0 )
+                return( ret );
+        }
+        else
+        {
+            ret = x509_crt_verify_top( parent, trust_ca, ca_crl, profile,
+                                       path_cnt + 1, &parent_flags,
+                                       f_vrfy, p_vrfy );
+            if( ret != 0 )
+                return( ret );
+        }
     }
 
     /* child is verified to be a child of the parent, call verify callback */
@@ -2188,27 +2210,44 @@ int mbedtls_x509_crt_verify_with_profile( mbedtls_x509_crt *crt,
         }
     }
 
-    /* Look for a parent upwards the chain */
+    /* Look for a parent in trusted CAs */
-    for( parent = crt->next; parent != NULL; parent = parent->next )
+    for( parent = trust_ca; parent != NULL; parent = parent->next )
     {
         if( x509_crt_check_parent( crt, parent, 0, pathlen == 0 ) == 0 )
             break;
     }
 
-    /* Are we part of the chain or at the top? */
     if( parent != NULL )
     {
-        ret = x509_crt_verify_child( crt, parent, trust_ca, ca_crl, profile,
+        ret = x509_crt_verify_top( crt, parent, ca_crl, profile,
-                                     pathlen, flags, f_vrfy, p_vrfy );
+                                   pathlen, flags, f_vrfy, p_vrfy );
         if( ret != 0 )
             return( ret );
     }
     else
     {
-        ret = x509_crt_verify_top( crt, trust_ca, ca_crl, profile,
+        /* Look for a parent upwards the chain */
-                                   pathlen, flags, f_vrfy, p_vrfy );
+        for( parent = crt->next; parent != NULL; parent = parent->next )
-        if( ret != 0 )
+        {
-            return( ret );
+            if( x509_crt_check_parent( crt, parent, 0, pathlen == 0 ) == 0 )
+                break;
+        }
+
+        /* Are we part of the chain or at the top? */
+        if( parent != NULL )
+        {
+            ret = x509_crt_verify_child( crt, parent, trust_ca, ca_crl, profile,
+                                         pathlen, flags, f_vrfy, p_vrfy );
+            if( ret != 0 )
+                return( ret );
+        }
+        else
+        {
+            ret = x509_crt_verify_top( crt, trust_ca, ca_crl, profile,
+                                       pathlen, flags, f_vrfy, p_vrfy );
+            if( ret != 0 )
+                return( ret );
+        }
     }
 
     if( *flags != 0 )

tests/suites/test_suite_x509parse.data

@@ -727,6 +727,10 @@ X509 Certificate verification callback: intermediate ca, root included
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECDSA_C:MBEDTLS_RSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECP_DP_SECP384R1_ENABLED:MBEDTLS_PKCS1_V15:MBEDTLS_SHA256_C
 x509_verify_callback:"data_files/server7_int-ca_ca2.crt":"data_files/test-ca_cat12.crt":0:"depth 2 - serial C1\:43\:E2\:7E\:62\:43\:CC\:E8 - subject C=NL, O=PolarSSL, CN=Polarssl Test EC CA\ndepth 1 - serial 0E - subject C=NL, O=PolarSSL, CN=PolarSSL Test Intermediate CA\ndepth 0 - serial 10 - subject C=NL, O=PolarSSL, CN=localhost\n"
 
+X509 Certificate verification callback: intermediate ca trusted
+depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECDSA_C:MBEDTLS_RSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECP_DP_SECP384R1_ENABLED:MBEDTLS_PKCS1_V15:MBEDTLS_SHA256_C
+x509_verify_callback:"data_files/server7_int-ca_ca2.crt":"data_files/test-int-ca.crt":0:"depth 1 - serial 0E - subject C=NL, O=PolarSSL, CN=PolarSSL Test Intermediate CA\ndepth 0 - serial 10 - subject C=NL, O=PolarSSL, CN=localhost\n"
+
 X509 Certificate verification callback: two intermediates
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECDSA_C:MBEDTLS_RSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECP_DP_SECP384R1_ENABLED:MBEDTLS_PKCS1_V15:MBEDTLS_SHA256_C
 x509_verify_callback:"data_files/server10_int3_int-ca2.crt":"data_files/test-ca_cat21.crt":0:"depth 3 - serial 00 - subject C=NL, O=PolarSSL, CN=PolarSSL Test CA\ndepth 2 - serial 0F - subject C=NL, O=PolarSSL, CN=PolarSSL Test Intermediate EC CA\ndepth 1 - serial 4D - subject C=UK, O=mbed TLS, CN=mbed TLS Test intermediate CA 3\ndepth 0 - serial 4B - subject CN=localhost\n"
@@ -735,6 +739,14 @@ X509 Certificate verification callback: two intermediates, root included
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECDSA_C:MBEDTLS_RSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECP_DP_SECP384R1_ENABLED:MBEDTLS_PKCS1_V15:MBEDTLS_SHA256_C
 x509_verify_callback:"data_files/server10_int3_int-ca2_ca.crt":"data_files/test-ca_cat21.crt":0:"depth 3 - serial 00 - subject C=NL, O=PolarSSL, CN=PolarSSL Test CA\ndepth 2 - serial 0F - subject C=NL, O=PolarSSL, CN=PolarSSL Test Intermediate EC CA\ndepth 1 - serial 4D - subject C=UK, O=mbed TLS, CN=mbed TLS Test intermediate CA 3\ndepth 0 - serial 4B - subject CN=localhost\n"
 
+X509 Certificate verification callback: two intermediates, top int trusted
+depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECDSA_C:MBEDTLS_RSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECP_DP_SECP384R1_ENABLED:MBEDTLS_PKCS1_V15:MBEDTLS_SHA256_C
+x509_verify_callback:"data_files/server10_int3_int-ca2.crt":"data_files/test-int-ca2.crt":0:"depth 2 - serial 0F - subject C=NL, O=PolarSSL, CN=PolarSSL Test Intermediate EC CA\ndepth 1 - serial 4D - subject C=UK, O=mbed TLS, CN=mbed TLS Test intermediate CA 3\ndepth 0 - serial 4B - subject CN=localhost\n"
+
+X509 Certificate verification callback: two intermediates, low int trusted
+depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_ECDSA_C:MBEDTLS_RSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_ECP_DP_SECP384R1_ENABLED:MBEDTLS_PKCS1_V15:MBEDTLS_SHA256_C
+x509_verify_callback:"data_files/server10_int3_int-ca2_ca.crt":"data_files/test-int-ca3.crt":0:"depth 1 - serial 4D - subject C=UK, O=mbed TLS, CN=mbed TLS Test intermediate CA 3\ndepth 0 - serial 4B - subject CN=localhost\n"
+
 X509 Parse Selftest
 depends_on:MBEDTLS_SHA1_C:MBEDTLS_PEM_PARSE_C:MBEDTLS_CERTS_C
 x509_selftest: