Only allow ephemeral RSA keys in export ciphersuites.

OpenSSL clients would tolerate temporary RSA keys in non-export
ciphersuites. It also had an option SSL_OP_EPHEMERAL_RSA which
enabled this server side. Remove both options as they are a
protocol violation.

Thanks to Karthikeyan Bhargavan for reporting this issue.
(CVE-2015-0204)
Reviewed-by: Matt Caswell <matt@openssl.org>

Conflicts:
	CHANGES
	doc/ssl/SSL_CTX_set_options.pod
	doc/ssl/SSL_CTX_set_tmp_rsa_callback.pod
	ssl/s3_srvr.c

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-0204

Change-Id: I034a600962e60a49bddab295ca5b3b0584182b8d

Author: snhenson

ssl/d1_srvr.c

@@ -449,24 +449,15 @@ int dtls1_accept(SSL *s)
 		case SSL3_ST_SW_KEY_EXCH_B:
 			alg_k = s->s3->tmp.new_cipher->algorithm_mkey;
 
-			/* clear this, it may get reset by
-			 * send_server_key_exchange */
-			if ((s->options & SSL_OP_EPHEMERAL_RSA)
-#ifndef OPENSSL_NO_KRB5
-				&& !(alg_k & SSL_kKRB5)
-#endif /* OPENSSL_NO_KRB5 */
-				)
-				/* option SSL_OP_EPHEMERAL_RSA sends temporary RSA key
-				 * even when forbidden by protocol specs
-				 * (handshake may fail as clients are not required to
-				 * be able to handle this) */
-				s->s3->tmp.use_rsa_tmp=1;
-			else
-				s->s3->tmp.use_rsa_tmp=0;
+			/*
+			 * clear this, it may get reset by
+			 * send_server_key_exchange
+			 */
+			s->s3->tmp.use_rsa_tmp=0;
 
 			/* only send if a DH key exchange or
 			 * RSA but we have a sign only certificate */
-			if (s->s3->tmp.use_rsa_tmp
+			if (
 			/* PSK: send ServerKeyExchange if PSK identity
 			 * hint if provided */
 #ifndef OPENSSL_NO_PSK

ssl/s3_clnt.c

@@ -1554,6 +1554,13 @@ int ssl3_get_key_exchange(SSL *s)
 #ifndef OPENSSL_NO_RSA
 	if (alg_k & SSL_kRSA)
 		{
+		/* Temporary RSA keys only allowed in export ciphersuites */
+		if (!SSL_C_IS_EXPORT(s->s3->tmp.new_cipher))
+			{
+			al=SSL_AD_UNEXPECTED_MESSAGE;
+			SSLerr(SSL_F_SSL3_GET_SERVER_CERTIFICATE,SSL_R_UNEXPECTED_MESSAGE);
+			goto f_err;
+			}
 		if ((rsa=RSA_new()) == NULL)
 			{
 			SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_MALLOC_FAILURE);

ssl/s3_srvr.c

@@ -444,20 +444,11 @@ int ssl3_accept(SSL *s)
 		case SSL3_ST_SW_KEY_EXCH_B:
 			alg_k = s->s3->tmp.new_cipher->algorithm_mkey;
 
-			/* clear this, it may get reset by
-			 * send_server_key_exchange */
-			if ((s->options & SSL_OP_EPHEMERAL_RSA)
-#ifndef OPENSSL_NO_KRB5
-				&& !(alg_k & SSL_kKRB5)
-#endif /* OPENSSL_NO_KRB5 */
-				)
-				/* option SSL_OP_EPHEMERAL_RSA sends temporary RSA key
-				 * even when forbidden by protocol specs
-				 * (handshake may fail as clients are not required to
-				 * be able to handle this) */
-				s->s3->tmp.use_rsa_tmp=1;
-			else
-				s->s3->tmp.use_rsa_tmp=0;
+			/*
+			 * clear this, it may get reset by
+			 * send_server_key_exchange
+			 */
+			s->s3->tmp.use_rsa_tmp=0;
 
 
 			/* only send if a DH key exchange, fortezza or
@@ -471,7 +462,7 @@ int ssl3_accept(SSL *s)
 			 * server certificate contains the server's
 			 * public key for key exchange.
 			 */
-			if (s->s3->tmp.use_rsa_tmp
+			if (0
 			/* PSK: send ServerKeyExchange if PSK identity
 			 * hint if provided */
 #ifndef OPENSSL_NO_PSK

ssl/ssl.h

@@ -590,9 +590,8 @@ struct ssl_session_st
 #define SSL_OP_SINGLE_ECDH_USE				0x00080000L
 /* If set, always create a new key when using tmp_dh parameters */
 #define SSL_OP_SINGLE_DH_USE				0x00100000L
-/* Set to always use the tmp_rsa key when doing RSA operations,
- * even when this violates protocol specs */
-#define SSL_OP_EPHEMERAL_RSA				0x00200000L
+/* Does nothing: retained for compatibiity */
+#define SSL_OP_EPHEMERAL_RSA				0x0
 /* Set on servers to choose the cipher according to the server's
  * preferences */
 #define SSL_OP_CIPHER_SERVER_PREFERENCE			0x00400000L