After the ClientHello has been sent or received and before the peer's

Finished message has been received, a change cipher spec may be received
and must be ignored. Add a flag to the record layer struct and set it at
the appropriate moments during the handshake so that we will ignore it.

ok jsing

4 files changed, 22 insertions, 8 deletions

diff --git a/lib/libssl/tls13_client.c b/lib/libssl/tls13_client.c
index ef4c3de75f4..b42167a58a1 100644
--- a/lib/libssl/tls13_client.c
+++ b/lib/libssl/tls13_client.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls13_client.c,v 1.25 2020/01/22 03:20:09 jsing Exp $ */
+/* $OpenBSD: tls13_client.c,v 1.26 2020/01/22 05:06:23 tb Exp $ */
 /*
  * Copyright (c) 2018, 2019 Joel Sing <jsing@openbsd.org>
  *
@@ -223,6 +223,7 @@ int
 tls13_client_hello_sent(struct tls13_ctx *ctx)
 {
 	tls13_record_layer_set_legacy_version(ctx->rl, TLS1_2_VERSION);
+	tls13_record_layer_allow_ccs(ctx->rl, 1);
 
 	return 1;
 }
@@ -750,6 +751,8 @@ tls13_server_finished_recv(struct tls13_ctx *ctx)
 	    &secrets->server_application_traffic))
 		goto err;
 
+	tls13_record_layer_allow_ccs(ctx->rl, 0);
+
 	ret = 1;
 
  err:
diff --git a/lib/libssl/tls13_internal.h b/lib/libssl/tls13_internal.h
index 1eb05b71007..fc1d6c1889f 100644
--- a/lib/libssl/tls13_internal.h
+++ b/lib/libssl/tls13_internal.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls13_internal.h,v 1.42 2020/01/22 02:39:45 tb Exp $ */
+/* $OpenBSD: tls13_internal.h,v 1.43 2020/01/22 05:06:23 tb Exp $ */
 /*
  * Copyright (c) 2018 Bob Beck <beck@openbsd.org>
  * Copyright (c) 2018 Theo Buehler <tb@openbsd.org>
@@ -117,6 +117,7 @@ struct tls13_record_layer *tls13_record_layer_new(tls13_read_cb wire_read,
     tls13_phh_recv_cb phh_recv_cb,
     tls13_phh_sent_cb phh_sent_cb, void *cb_arg);
 void tls13_record_layer_free(struct tls13_record_layer *rl);
+void tls13_record_layer_allow_ccs(struct tls13_record_layer *rl, int allow);
 void tls13_record_layer_rbuf(struct tls13_record_layer *rl, CBS *cbs);
 void tls13_record_layer_set_aead(struct tls13_record_layer *rl,
     const EVP_AEAD *aead);
diff --git a/lib/libssl/tls13_record_layer.c b/lib/libssl/tls13_record_layer.c
index 600990a878a..ef558d52df6 100644
--- a/lib/libssl/tls13_record_layer.c
+++ b/lib/libssl/tls13_record_layer.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls13_record_layer.c,v 1.20 2020/01/22 02:39:45 tb Exp $ */
+/* $OpenBSD: tls13_record_layer.c,v 1.21 2020/01/22 05:06:23 tb Exp $ */
 /*
  * Copyright (c) 2018, 2019 Joel Sing <jsing@openbsd.org>
  *
@@ -29,7 +29,8 @@ static ssize_t tls13_record_layer_write_record(struct tls13_record_layer *rl,
 
 struct tls13_record_layer {
 	uint16_t legacy_version;
-	int change_cipher_spec_seen;
+	int ccs_allowed;
+	int ccs_seen;
 	int handshake_completed;
 	int phh;
 
@@ -200,6 +201,12 @@ tls13_record_layer_update_nonce(struct tls13_secret *nonce,
 }
 
 void
+tls13_record_layer_allow_ccs(struct tls13_record_layer *rl, int allow)
+{
+	rl->ccs_allowed = allow;
+}
+
+void
 tls13_record_layer_set_aead(struct tls13_record_layer *rl,
     const EVP_AEAD *aead)
 {
@@ -756,8 +763,7 @@ tls13_record_layer_read_record(struct tls13_record_layer *rl)
 	 * ignored.
 	 */
 	if (content_type == SSL3_RT_CHANGE_CIPHER_SPEC) {
-		/* XXX - need to check after ClientHello, before Finished. */
-		if (rl->handshake_completed || rl->change_cipher_spec_seen)
+		if (!rl->ccs_allowed || rl->ccs_seen)
 			return tls13_send_alert(rl, SSL_AD_UNEXPECTED_MESSAGE);
 		if (!tls13_record_content(rl->rrec, &cbs))
 			return tls13_send_alert(rl, TLS1_AD_DECODE_ERROR);
@@ -765,7 +771,7 @@ tls13_record_layer_read_record(struct tls13_record_layer *rl)
 			return tls13_send_alert(rl, TLS1_AD_DECODE_ERROR);
 		if (ccs != 1)
 			return tls13_send_alert(rl, SSL_AD_ILLEGAL_PARAMETER);
-		rl->change_cipher_spec_seen = 1;
+		rl->ccs_seen = 1;
 		tls13_record_layer_rrec_free(rl);
 		return TLS13_IO_WANT_POLLIN;
 	}
diff --git a/lib/libssl/tls13_server.c b/lib/libssl/tls13_server.c
index 10d85a62b3c..fc3e80ad587 100644
--- a/lib/libssl/tls13_server.c
+++ b/lib/libssl/tls13_server.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls13_server.c,v 1.4 2020/01/22 02:21:05 beck Exp $ */
+/* $OpenBSD: tls13_server.c,v 1.5 2020/01/22 05:06:23 tb Exp $ */
 /*
  * Copyright (c) 2019 Joel Sing <jsing@openbsd.org>
  *
@@ -81,6 +81,8 @@ tls13_legacy_accept(SSL *ssl)
 int
 tls13_client_hello_recv(struct tls13_ctx *ctx)
 {
+	tls13_record_layer_allow_ccs(ctx->rl, 1);
+
 	return 0;
 }
 
@@ -135,6 +137,8 @@ tls13_client_certificate_verify_recv(struct tls13_ctx *ctx)
 int
 tls13_client_finished_recv(struct tls13_ctx *ctx)
 {
+	tls13_record_layer_allow_ccs(ctx->rl, 0);
+
 	return 0;
 }