s23_clnt.c: ensure interoperability by maitaining client "version capability"

vector contiguous.
PR: 2802

CHANGES

@@ -288,7 +288,17 @@
      is enable if DEBUG_UNUSED is set. Add to several functions in evp.h
      whose return value is often ignored. 
      [Steve Henson]
-  
+
+ Changes between 1.0.1a and 1.0.1b [xx XXX xxxx]
+
+  *) In order to ensure interoperabilty SSL_OP_NO_protocolX does not
+     disable just protocol X, but all protocols above X *if* there are
+     protocols *below* X still enabled. In more practical terms it means
+     that if application wants to disable TLS1.0 in favor of TLS1.1 and
+     above, it's not sufficient to pass SSL_OP_NO_TLSv1, one has to pass
+     SSL_OP_NO_TLSv1|SSL_OP_NO_SSLv3|SSL_OP_NO_SSLv2.
+     [Andy Polyakov]
+
  Changes between 1.0.1 and 1.0.1a [19 Apr 2012]
 
   *) Check for potentially exploitable overflows in asn1_d2i_read_bio

ssl/s23_clnt.c

@@ -282,32 +282,51 @@ static int ssl23_client_hello(SSL *s)
 	SSL_COMP *comp;
 #endif
 	int ret;
+	unsigned long mask, options = s->options;
 
-	ssl2_compat = (s->options & SSL_OP_NO_SSLv2) ? 0 : 1;
+	ssl2_compat = (options & SSL_OP_NO_SSLv2) ? 0 : 1;
 
 	if (ssl2_compat && ssl23_no_ssl2_ciphers(s))
 		ssl2_compat = 0;
 
-	if (!(s->options & SSL_OP_NO_TLSv1_2))
-		{
-		version = TLS1_2_VERSION;
-		}
-	else if (!(s->options & SSL_OP_NO_TLSv1_1))
-		{
+	/*
+	 * SSL_OP_NO_X disables all protocols above X *if* there are
+	 * some protocols below X enabled. This is required in order
+	 * to maintain "version capability" vector contiguous. So
+	 * that if application wants to disable TLS1.0 in favour of
+	 * TLS1>=1, it would be insufficient to pass SSL_NO_TLSv1, the
+	 * answer is SSL_OP_NO_TLSv1|SSL_OP_NO_SSLv3|SSL_OP_NO_SSLv2.
+	 */
+	mask =	SSL_OP_NO_TLSv1_1|SSL_OP_NO_TLSv1
+#if !defined(OPENSSL_NO_SSL3)
+		|SSL_OP_NO_SSLv3
+#endif
+#if !defined(OPENSSL_NO_SSL2)
+		|(ssl2_compat?SSL_OP_NO_SSLv2:0)
+#endif
+		;
+#if !defined(OPENSSL_NO_TLS1_2_CLIENT)
+	version = TLS1_2_VERSION;
+
+	if ((options & SSL_OP_NO_TLSv1_2) && (options & mask) != mask)
 		version = TLS1_1_VERSION;
-		}
-	else if (!(s->options & SSL_OP_NO_TLSv1))
-		{
+#else
+	version = TLS1_1_VERSION;
+#endif
+	mask &= ~SSL_OP_NO_TLSv1_1;
+	if ((options & SSL_OP_NO_TLSv1_1) && (options & mask) != mask)
 		version = TLS1_VERSION;
-		}
-	else if (!(s->options & SSL_OP_NO_SSLv3))
-		{
+	mask &= ~SSL_OP_NO_TLSv1;
+#if !defined(OPENSSL_NO_SSL3)
+	if ((options & SSL_OP_NO_TLSv1) && (options & mask) != mask)
 		version = SSL3_VERSION;
-		}
-	else if (!(s->options & SSL_OP_NO_SSLv2))
-		{
+	mask &= ~SSL_OP_NO_SSLv3;
+#endif
+#if !defined(OPENSSL_NO_SSL2)
+	if ((options & SSL_OP_NO_SSLv3) && (options & mask) != mask)
 		version = SSL2_VERSION;
-		}
+#endif
+
 #ifndef OPENSSL_NO_TLSEXT
 	if (version != SSL2_VERSION)
 		{