Support TLS_FALLBACK_SCSV.

Reviewed-by: Rich Salz <rsalz@openssl.org>

1 files changed, 47 insertions, 16 deletions

diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c
index f779ce66d7..27819b452f 100644
--- a/ssl/ssl_lib.c
+++ b/ssl/ssl_lib.c
@@ -1464,12 +1464,14 @@ int ssl_cipher_list_to_bytes(SSL *s,STACK_OF(SSL_CIPHER) *sk,unsigned char *p,
 	SSL_CIPHER *c;
 	CERT *ct = s->cert;
 	unsigned char *q;
-	int no_scsv = s->renegotiate;
+	int empty_reneg_info_scsv = !s->renegotiate;
 	/* Set disabled masks for this session */
 	ssl_set_client_disabled(s);
 
 	if (sk == NULL) return(0);
 	q=p;
+	if (put_cb == NULL)
+		put_cb = s->method->put_cipher_by_char;
 
 	for (i=0; i<sk_SSL_CIPHER_num(sk); i++)
 		{
@@ -1482,29 +1484,40 @@ int ssl_cipher_list_to_bytes(SSL *s,STACK_OF(SSL_CIPHER) *sk,unsigned char *p,
 #ifdef OPENSSL_SSL_DEBUG_BROKEN_PROTOCOL
 		if (c->id == SSL3_CK_SCSV)
 			{
-			if (no_scsv)
+			if (!empty_reneg_info_scsv)
 				continue;
 			else
-				no_scsv = 1;
+				empty_reneg_info_scsv = 0;
 			}
 #endif
-		j = put_cb ? put_cb(c,p) : ssl_put_cipher_by_char(s,c,p);
+		j = put_cb(c,p);
 		p+=j;
 		}
-	/* If p == q, no ciphers and caller indicates an error. Otherwise
-	 * add SCSV if not renegotiating.
-	 */
-	if (p != q && !no_scsv)
+	/* If p == q, no ciphers; caller indicates an error.
+	 * Otherwise, add applicable SCSVs. */
+	if (p != q)
 		{
-		static SSL_CIPHER scsv =
+		if (empty_reneg_info_scsv)
 			{
-			0, NULL, SSL3_CK_SCSV, 0, 0, 0, 0, 0, 0, 0, 0, 0
-			};
-		j = put_cb ? put_cb(&scsv,p) : ssl_put_cipher_by_char(s,&scsv,p);
-		p+=j;
+			static SSL_CIPHER scsv =
+				{
+				0, NULL, SSL3_CK_SCSV, 0, 0, 0, 0, 0, 0, 0, 0, 0
+				};
+			j = put_cb(&scsv,p);
+			p+=j;
 #ifdef OPENSSL_RI_DEBUG
-		fprintf(stderr, "SCSV sent by client\n");
+			fprintf(stderr, "TLS_EMPTY_RENEGOTIATION_INFO_SCSV sent by client\n");
 #endif
+			}
+		if (s->mode & SSL_MODE_SEND_FALLBACK_SCSV)
+			{
+			static SSL_CIPHER scsv =
+				{
+				0, NULL, SSL3_CK_FALLBACK_SCSV, 0, 0, 0, 0, 0, 0, 0, 0, 0
+				};
+			j = put_cb(&scsv,p);
+			p+=j;
+			}
 		}
 
 	return(p-q);
@@ -1516,11 +1529,12 @@ STACK_OF(SSL_CIPHER) *ssl_bytes_to_cipher_list(SSL *s,unsigned char *p,int num,
 	const SSL_CIPHER *c;
 	STACK_OF(SSL_CIPHER) *sk;
 	int i,n;
+
 	if (s->s3)
 		s->s3->send_connection_binding = 0;
 
 	n=ssl_put_cipher_by_char(s,NULL,NULL);
-	if ((num%n) != 0)
+	if (n == 0 || (num%n) != 0)
 		{
 		SSLerr(SSL_F_SSL_BYTES_TO_CIPHER_LIST,SSL_R_ERROR_IN_RECEIVED_CIPHER_LIST);
 		return(NULL);
@@ -1545,7 +1559,7 @@ STACK_OF(SSL_CIPHER) *ssl_bytes_to_cipher_list(SSL *s,unsigned char *p,int num,
 
 	for (i=0; i<num; i+=n)
 		{
-		/* Check for SCSV */
+		/* Check for TLS_EMPTY_RENEGOTIATION_INFO_SCSV */
 		if (s->s3 && (n != 3 || !p[0]) &&
 			(p[n-2] == ((SSL3_CK_SCSV >> 8) & 0xff)) &&
 			(p[n-1] == (SSL3_CK_SCSV & 0xff)))
@@ -1565,6 +1579,23 @@ STACK_OF(SSL_CIPHER) *ssl_bytes_to_cipher_list(SSL *s,unsigned char *p,int num,
 			continue;
 			}
 
+		/* Check for TLS_FALLBACK_SCSV */
+		if ((n != 3 || !p[0]) &&
+			(p[n-2] == ((SSL3_CK_FALLBACK_SCSV >> 8) & 0xff)) &&
+			(p[n-1] == (SSL3_CK_FALLBACK_SCSV & 0xff)))
+			{
+			/* The SCSV indicates that the client previously tried a higher version.
+			 * Fail if the current version is an unexpected downgrade. */
+			if (!SSL_ctrl(s, SSL_CTRL_CHECK_PROTO_VERSION, 0, NULL))
+				{
+				SSLerr(SSL_F_SSL_BYTES_TO_CIPHER_LIST,SSL_R_INAPPROPRIATE_FALLBACK);
+				if (s->s3)
+					ssl3_send_alert(s,SSL3_AL_FATAL,SSL_AD_INAPPROPRIATE_FALLBACK);
+				goto err;
+				}
+			continue;
+			}
+
 		c=ssl_get_cipher_by_char(s,p);
 		p+=n;
 		if (c != NULL)