From: Dr. Stephen Henson <steve@openssl.org>
Date: Thu, 9 Feb 2012 15:41:44 +0000 (+0000)
Subject: Modify client hello version when renegotiating to enhance interop with
X-Git-Tag: OpenSSL_1_0_1-beta3~24
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=fc6800d19f4a0ca852c07128952d4c347d2d7065;p=openssl

Modify client hello version when renegotiating to enhance interop with
some servers.
---

diff --git a/CHANGES b/CHANGES
index 9907aef8f3..47d76cb81a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,13 @@
 
  Changes between 1.0.0f and 1.0.1  [xx XXX xxxx]
 
+  *) Some servers which support TLS 1.0 can choke if we initially indicate
+     support for TLS 1.2 and later renegotiate using TLS 1.0 in the RSA
+     encrypted premaster secret. As a workaround use the maximum pemitted
+     client version in client hello, this should keep such servers happy
+     and still work with previous versions of OpenSSL.
+     [Steve Henson]
+
   *) Add support for TLS/DTLS heartbeats.
      [Robin Seggelmann <seggelmann@fh-muenster.de>]
 
diff --git a/ssl/s3_clnt.c b/ssl/s3_clnt.c
index ff1cff23d0..4511a914a4 100644
--- a/ssl/s3_clnt.c
+++ b/ssl/s3_clnt.c
@@ -689,9 +689,43 @@ int ssl3_client_hello(SSL *s)
 		/* Do the message type and length last */
 		d=p= &(buf[4]);
 
+		/* version indicates the negotiated version: for example from
+		 * an SSLv2/v3 compatible client hello). The client_version
+		 * field is the maximum version we permit and it is also
+		 * used in RSA encrypted premaster secrets. Some servers can
+		 * choke if we initially report a higher version then
+		 * renegotiate to a lower one in the premaster secret. This
+		 * didn't happen with TLS 1.0 as most servers supported it
+		 * but it can with TLS 1.1 or later if the server only supports
+		 * 1.0.
+		 *
+		 * Possible scenario with previous logic:
+		 * 	1. Client hello indicates TLS 1.2
+		 * 	2. Server hello says TLS 1.0
+		 *	3. RSA encrypted premaster secret uses 1.2.
+		 * 	4. Handhaked proceeds using TLS 1.0.
+		 *	5. Server sends hello request to renegotiate.
+		 *	6. Client hello indicates TLS v1.0 as we now
+		 *	   know that is maximum server supports.
+		 *	7. Server chokes on RSA encrypted premaster secret
+		 *	   containing version 1.0.
+		 *
+		 * For interoperability it should be OK to always use the
+		 * maximum version we support in client hello and then rely
+		 * on the checking of version to ensure the servers isn't
+		 * being inconsistent: for example initially negotiating with
+		 * TLS 1.0 and renegotiating with TLS 1.2. We do this by using
+		 * client_version in client hello and not resetting it to
+		 * the negotiated version.
+		 */
+#if 0
 		*(p++)=s->version>>8;
 		*(p++)=s->version&0xff;
 		s->client_version=s->version;
+#else
+		*(p++)=s->client_version>>8;
+		*(p++)=s->client_version&0xff;
+#endif
 
 		/* Random stuff */
 		memcpy(p,s->s3->client_random,SSL3_RANDOM_SIZE);