Fix undefined shifts

- in x509_profile_check_pk_alg
- in x509_profile_check_md_alg
- in x509_profile_check_key

and in ssl_cli.c : unsigned char gets promoted to signed integer

ChangeLog

@@ -1,5 +1,11 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS 2.7.6 branch released xxxx-xx-xx
+
+Bugfix
+   * Fix undefined shifts with negative values in certificates parsing
+     (found by Catena cyber using oss-fuzz)
+
 = mbed TLS 2.7.5 branch released 2018-07-25
 
 Security

library/ssl_cli.c

@@ -3315,7 +3315,7 @@ static int ssl_parse_new_session_ticket( mbedtls_ssl_context *ssl )
 
     msg = ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl );
 
-    lifetime = ( msg[0] << 24 ) | ( msg[1] << 16 ) |
+    lifetime = ( ((uint32_t) msg[0]) << 24 ) | ( msg[1] << 16 ) |
                ( msg[2] << 8 ) | ( msg[3] );
 
     ticket_len = ( msg[4] << 8 ) | ( msg[5] );

library/x509_crt.c

@@ -152,6 +152,9 @@ const mbedtls_x509_crt_profile mbedtls_x509_crt_profile_suiteb =
 static int x509_profile_check_md_alg( const mbedtls_x509_crt_profile *profile,
                                       mbedtls_md_type_t md_alg )
 {
+    if( md_alg == MBEDTLS_MD_NONE )
+        return( -1 );
+
     if( ( profile->allowed_mds & MBEDTLS_X509_ID_FLAG( md_alg ) ) != 0 )
         return( 0 );
 
@@ -165,6 +168,9 @@ static int x509_profile_check_md_alg( const mbedtls_x509_crt_profile *profile,
 static int x509_profile_check_pk_alg( const mbedtls_x509_crt_profile *profile,
                                       mbedtls_pk_type_t pk_alg )
 {
+    if( pk_alg == MBEDTLS_PK_NONE )
+        return( -1 );
+
     if( ( profile->allowed_pks & MBEDTLS_X509_ID_FLAG( pk_alg ) ) != 0 )
         return( 0 );
 
@@ -196,6 +202,9 @@ static int x509_profile_check_key( const mbedtls_x509_crt_profile *profile,
     {
         mbedtls_ecp_group_id gid = mbedtls_pk_ec( *pk )->grp.id;
 
+        if( gid == MBEDTLS_ECP_DP_NONE )
+            return( -1 );
+
         if( ( profile->allowed_curves & MBEDTLS_X509_ID_FLAG( gid ) ) != 0 )
             return( 0 );