Allow disabling HelloVerifyRequest

include/polarssl/ssl.h

@@ -1136,6 +1136,16 @@ typedef int ssl_cookie_check_t( void *ctx,
  * \brief           Register callbacks for DTLS cookies
  *                  (Server only. DTLS only.)
  *
+ *                  Default: dummy callbacks that fail, to force you to
+ *                  register working callbacks (and initialize their context).
+ *
+ *                  To disable HelloVerifyRequest, register NULL callbacks.
+ *
+ * \warning         Disabling hello verification allows your server to be used
+ *                  for amplification in DoS attacks against other hosts.
+ *                  Only disable if you known this can't happen in your
+ *                  particular environment.
+ *
  * \param ssl               SSL context
  * \param f_cookie_write    Cookie write callback
  * \param f_cookie_check    Cookie check callback

library/ssl_srv.c

@@ -1441,28 +1441,33 @@ static int ssl_parse_client_hello( ssl_context *ssl )
                        buf + cookie_offset + 1, cookie_len );
 
 #if defined(POLARSSL_SSL_DTLS_HELLO_VERIFY)
-        if( ssl->f_cookie_check( ssl->p_cookie,
+        if( ssl->f_cookie_check != NULL )
-                                 buf + cookie_offset + 1, cookie_len,
-                                 ssl->cli_id, ssl->cli_id_len ) != 0 )
         {
-            SSL_DEBUG_MSG( 2, ( "client hello, cookie verification failed" ) );
+            if( ssl->f_cookie_check( ssl->p_cookie,
-            ssl->handshake->verify_cookie_len = 1;
+                                     buf + cookie_offset + 1, cookie_len,
+                                     ssl->cli_id, ssl->cli_id_len ) != 0 )
+            {
+                SSL_DEBUG_MSG( 2, ( "cookie verification failed" ) );
+                ssl->handshake->verify_cookie_len = 1;
+            }
+            else
+            {
+                SSL_DEBUG_MSG( 2, ( "cookie verification passed" ) );
+                ssl->handshake->verify_cookie_len = 0;
+            }
         }
         else
-        {
-            SSL_DEBUG_MSG( 2, ( "client hello, cookie verification passed" ) );
-            ssl->handshake->verify_cookie_len = 0;
-        }
-#else
-        /* We know we didn't send a cookie, so it should be empty */
-        if( cookie_len != 0 )
-        {
-            SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
-            return( POLARSSL_ERR_SSL_BAD_HS_CLIENT_HELLO );
-        }
-
-        SSL_DEBUG_MSG( 2, ( "client hello, cookie verification skipped" ) );
 #endif /* POLARSSL_SSL_DTLS_HELLO_VERIFY */
+        {
+            /* We know we didn't send a cookie, so it should be empty */
+            if( cookie_len != 0 )
+            {
+                SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
+                return( POLARSSL_ERR_SSL_BAD_HS_CLIENT_HELLO );
+            }
+
+            SSL_DEBUG_MSG( 2, ( "cookie verification skipped" ) );
+        }
     }
 #endif /* POLARSSL_SSL_PROTO_DTLS */
 
@@ -1982,6 +1987,13 @@ static int ssl_write_hello_verify_request( ssl_context *ssl )
     SSL_DEBUG_BUF( 3, "server version", (unsigned char *) p, 2 );
     p += 2;
 
+    /* If we get here, f_cookie_check is not null */
+    if( ssl->f_cookie_write == NULL )
+    {
+        SSL_DEBUG_MSG( 1, ( "inconsistent cookie callbacks" ) );
+        return( POLARSSL_ERR_SSL_INTERNAL_ERROR );
+    }
+
     /* Skip length byte until we know the length */
     cookie_len_byte = p++;
 

library/ssl_tls.c

@@ -3607,6 +3607,35 @@ static int ssl_handshake_init( ssl_context *ssl )
     return( 0 );
 }
 
+#if defined(POLARSSL_SSL_DTLS_HELLO_VERIFY)
+/* Dummy cookie callbacks for defaults */
+static int ssl_cookie_write_dummy( void *ctx,
+                      unsigned char **p, unsigned char *end,
+                      const unsigned char *cli_id, size_t cli_id_len )
+{
+    ((void) ctx);
+    ((void) p);
+    ((void) end);
+    ((void) cli_id);
+    ((void) cli_id_len);
+
+    return( POLARSSL_ERR_SSL_FEATURE_UNAVAILABLE );
+}
+
+static int ssl_cookie_check_dummy( void *ctx,
+                      const unsigned char *cookie, size_t cookie_len,
+                      const unsigned char *cli_id, size_t cli_id_len )
+{
+    ((void) ctx);
+    ((void) cookie);
+    ((void) cookie_len);
+    ((void) cli_id);
+    ((void) cli_id_len);
+
+    return( POLARSSL_ERR_SSL_FEATURE_UNAVAILABLE );
+}
+#endif /* POLARSSL_SSL_DTLS_HELLO_VERIFY */
+
 /*
  * Initialize an SSL context
  */
@@ -3670,6 +3699,11 @@ int ssl_init( ssl_context *ssl )
     ssl->curve_list = ecp_grp_id_list( );
 #endif
 
+#if defined(POLARSSL_SSL_DTLS_HELLO_VERIFY)
+    ssl->f_cookie_write = ssl_cookie_write_dummy;
+    ssl->f_cookie_check = ssl_cookie_check_dummy;
+#endif
+
     if( ( ret = ssl_handshake_init( ssl ) ) != 0 )
         return( ret );