From 29ee67c205855e848a0a26e6d0e4f65b6b943e0a Mon Sep 17 00:00:00 2001

From: Daiki Ueno <ueno@gnu.org>

Date: Sat, 22 Aug 2020 17:19:39 +0200

Subject: [PATCH] handshake: reject no_renegotiation alert if handshake is

 incomplete

If the initial handshake is incomplete and the server sends a

no_renegotiation alert, the client should treat it as a fatal error

even if its level is warning.  Otherwise the same handshake

state (e.g., DHE parameters) are reused in the next gnutls_handshake

call, if it is called in the loop idiom:

  do {

          ret = gnutls_handshake(session);

  } while (ret < 0 && gnutls_error_is_fatal(ret) == 0);

Signed-off-by: Daiki Ueno <ueno@gnu.org>

---

 ...a04b3d3f7dcc0ab4571cf0df3b67ab7e1005e9e7a8 | Bin 0 -> 671 bytes

 ...1da801fb3c6d1f7f846f227721e221adea08aa319c | Bin 0 -> 729 bytes

 lib/gnutls_int.h                              |   1 +

 lib/handshake.c                               |  48 +++++++++++++-----

 4 files changed, 36 insertions(+), 13 deletions(-)

 create mode 100644 fuzz/gnutls_client_fuzzer.in/00ea40761ce11e769f1817a04b3d3f7dcc0ab4571cf0df3b67ab7e1005e9e7a8

 create mode 100644 fuzz/gnutls_psk_client_fuzzer.in/b16434290b77e13d7a983d1da801fb3c6d1f7f846f227721e221adea08aa319c

diff --git a/lib/gnutls_int.h b/lib/gnutls_int.h

index bb6c19713..31cec5c0c 100644

--- a/lib/gnutls_int.h

+++ b/lib/gnutls_int.h

@@ -1370,6 +1370,7 @@ typedef struct {

 #define HSK_RECORD_SIZE_LIMIT_RECEIVED (1<<26) /* server: record_size_limit extension was seen but not accepted yet */

 #define HSK_OCSP_REQUESTED (1<<27) /* server: client requested OCSP stapling */

 #define HSK_CLIENT_OCSP_REQUESTED (1<<28) /* client: server requested OCSP stapling */

+#define HSK_SERVER_HELLO_RECEIVED (1<<29) /* client: Server Hello message has been received */

 	/* The hsk_flags are for use within the ongoing handshake;

 	 * they are reset to zero prior to handshake start by gnutls_handshake. */

diff --git a/lib/handshake.c b/lib/handshake.c

index b40f84b3d..ce2d160e2 100644

--- a/lib/handshake.c

+++ b/lib/handshake.c

@@ -2061,6 +2061,8 @@ read_server_hello(gnutls_session_t session,

 	if (ret < 0)

 		return gnutls_assert_val(ret);

+	session->internals.hsk_flags |= HSK_SERVER_HELLO_RECEIVED;

+

 	return 0;

 }

@@ -2585,16 +2587,42 @@ int gnutls_rehandshake(gnutls_session_t session)

 	return 0;

 }

+/* This function checks whether the error code should be treated fatal

+ * or not, and also does the necessary state transition.  In

+ * particular, in the case of a rehandshake abort it resets the

+ * handshake's internal state.

+ */

 inline static int

 _gnutls_abort_handshake(gnutls_session_t session, int ret)

 {

-	if (((ret == GNUTLS_E_WARNING_ALERT_RECEIVED) &&

-	     (gnutls_alert_get(session) == GNUTLS_A_NO_RENEGOTIATION))

-	    || ret == GNUTLS_E_GOT_APPLICATION_DATA)

-		return 0;

+	switch (ret) {

+	case GNUTLS_E_WARNING_ALERT_RECEIVED:

+		if (gnutls_alert_get(session) == GNUTLS_A_NO_RENEGOTIATION) {

+			/* The server always toleretes a "no_renegotiation" alert. */

+			if (session->security_parameters.entity == GNUTLS_SERVER) {

+				STATE = STATE0;

+				return ret;

+			}

+

+			/* The client should tolerete a "no_renegotiation" alert only if:

+			 * - the initial handshake has completed, or

+			 * - a Server Hello is not yet received

+			 */

+			if (session->internals.initial_negotiation_completed ||

+			    !(session->internals.hsk_flags & HSK_SERVER_HELLO_RECEIVED)) {

+				STATE = STATE0;

+				return ret;

+			}

-	/* this doesn't matter */

-	return GNUTLS_E_INTERNAL_ERROR;

+			return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET);

+		}

+		return ret;

+	case GNUTLS_E_GOT_APPLICATION_DATA:

+		STATE = STATE0;

+		return ret;

+	default:

+		return ret;

+	}

 }

@@ -2756,13 +2784,7 @@ int gnutls_handshake(gnutls_session_t session)

 	}

 	if (ret < 0) {

-		/* In the case of a rehandshake abort

-		 * we should reset the handshake's internal state.

-		 */

-		if (_gnutls_abort_handshake(session, ret) == 0)

-			STATE = STATE0;

-

-		return ret;

+		return _gnutls_abort_handshake(session, ret);

 	}

 	/* clear handshake buffer */

-- 

2.26.2