Implement ALPN server-side

include/polarssl/ssl.h

@@ -320,6 +320,7 @@
 #define SSL_ALERT_MSG_UNSUPPORTED_EXT      110  /* 0x6E */
 #define SSL_ALERT_MSG_UNRECOGNIZED_NAME    112  /* 0x70 */
 #define SSL_ALERT_MSG_UNKNOWN_PSK_IDENTITY 115  /* 0x73 */
+#define SSL_ALERT_MSG_NO_APPLICATION_PROTOCOL 120 /* 0x78 */
 
 #define SSL_HS_HELLO_REQUEST            0
 #define SSL_HS_CLIENT_HELLO             1

library/ssl_srv.c

@@ -683,6 +683,69 @@ static int ssl_parse_session_ticket_ext( ssl_context *ssl,
 }
 #endif /* POLARSSL_SSL_SESSION_TICKETS */
 
+#if defined(POLARSSL_SSL_ALPN)
+static int ssl_parse_alpn_ext( ssl_context *ssl,
+                               unsigned char *buf, size_t len )
+{
+    size_t list_len, cur_len;
+    const unsigned char *theirs, *start, *end;
+    const char **ours;
+
+    /* If ALPN not configured, just ignore the extension */
+    if( ssl->alpn_list == NULL )
+        return( 0 );
+
+    /*
+     * opaque ProtocolName<1..2^8-1>;
+     *
+     * struct {
+     *     ProtocolName protocol_name_list<2..2^16-1>
+     * } ProtocolNameList;
+     */
+
+    /* Min length is 2 (list_len) + 1 (name_len) + 1 (name) */
+    if( len < 4 )
+        return( POLARSSL_ERR_SSL_BAD_HS_CLIENT_HELLO );
+
+    list_len = ( buf[0] << 8 ) | buf[1];
+    if( list_len != len - 2 )
+        return( POLARSSL_ERR_SSL_BAD_HS_CLIENT_HELLO );
+
+    /*
+     * Use our order of preference
+     */
+    start = buf + 2;
+    end = buf + len;
+    for( ours = ssl->alpn_list; *ours != NULL; ours++ )
+    {
+        for( theirs = start; theirs != end; theirs += cur_len )
+        {
+            /* If the list is well formed, we should get equality first */
+            if( theirs > end )
+                return( POLARSSL_ERR_SSL_BAD_HS_CLIENT_HELLO );
+
+            cur_len = *theirs++;
+
+            /* Empty strings MUST NOT be included */
+            if( cur_len == 0 )
+                return( POLARSSL_ERR_SSL_BAD_HS_CLIENT_HELLO );
+
+            if( cur_len == strlen( *ours ) &&
+                memcmp( theirs, *ours, cur_len ) == 0 )
+            {
+                ssl->alpn_chosen = *ours;
+                return( 0 );
+            }
+        }
+    }
+
+    /* If we get there, no match was found */
+    ssl_send_alert_message( ssl, SSL_ALERT_LEVEL_FATAL,
+                            SSL_ALERT_MSG_NO_APPLICATION_PROTOCOL );
+    return( POLARSSL_ERR_SSL_BAD_HS_CLIENT_HELLO );
+}
+#endif /* POLARSSL_SSL_ALPN */
+
 /*
  * Auxiliary functions for ServerHello parsing and related actions
  */
@@ -1385,6 +1448,16 @@ static int ssl_parse_client_hello( ssl_context *ssl )
             break;
 #endif /* POLARSSL_SSL_SESSION_TICKETS */
 
+#if defined(POLARSSL_SSL_ALPN)
+        case TLS_EXT_ALPN:
+            SSL_DEBUG_MSG( 3, ( "found ALPN extension" ) );
+
+            ret = ssl_parse_alpn_ext( ssl, ext + 4, ext_size );
+            if( ret != 0 )
+                return( ret );
+            break;
+#endif /* POLARSSL_SSL_SESSION_TICKETS */
+
         default:
             SSL_DEBUG_MSG( 3, ( "unknown extension found: %d (ignoring)",
                            ext_id ) );
@@ -1625,6 +1698,42 @@ static void ssl_write_supported_point_formats_ext( ssl_context *ssl,
 }
 #endif /* POLARSSL_ECDH_C || POLARSSL_ECDSA_C */
 
+#if defined(POLARSSL_SSL_ALPN )
+static void ssl_write_alpn_ext( ssl_context *ssl,
+                                unsigned char *buf, size_t *olen )
+{
+    if( ssl->alpn_chosen == NULL )
+    {
+        *olen = 0;
+        return;
+    }
+
+    SSL_DEBUG_MSG( 3, ( "server hello, alpn extension" ) );
+
+    /*
+     * 0 . 1    ext identifier
+     * 2 . 3    ext length
+     * 4 . 5    protocol list length
+     * 6 . 6    protocol name length
+     * 7 . 7+n  protocol name
+     */
+    buf[0] = (unsigned char)( ( TLS_EXT_ALPN >> 8 ) & 0xFF );
+    buf[1] = (unsigned char)( ( TLS_EXT_ALPN      ) & 0xFF );
+
+    *olen = 7 + strlen( ssl->alpn_chosen );
+
+    buf[2] = (unsigned char)( ( ( *olen - 4 ) >> 8 ) & 0xFF );
+    buf[3] = (unsigned char)( ( ( *olen - 4 )      ) & 0xFF );
+
+    buf[4] = (unsigned char)( ( ( *olen - 6 ) >> 8 ) & 0xFF );
+    buf[5] = (unsigned char)( ( ( *olen - 6 )      ) & 0xFF );
+
+    buf[6] = (unsigned char)( ( ( *olen - 7 )      ) & 0xFF );
+
+    memcpy( buf + 7, ssl->alpn_chosen, *olen - 7 );
+}
+#endif /* POLARSSL_ECDH_C || POLARSSL_ECDSA_C */
+
 static int ssl_write_server_hello( ssl_context *ssl )
 {
 #if defined(POLARSSL_HAVE_TIME)
@@ -1791,6 +1900,11 @@ static int ssl_write_server_hello( ssl_context *ssl )
     ext_len += olen;
 #endif
 
+#if defined(POLARSSL_SSL_ALPN)
+    ssl_write_alpn_ext( ssl, p + 2 + ext_len, &olen );
+    ext_len += olen;
+#endif
+
     SSL_DEBUG_MSG( 3, ( "server hello, total extension length: %d", ext_len ) );
 
     *p++ = (unsigned char)( ( ext_len >> 8 ) & 0xFF );