Fix some client side transition logic

Fixed some issues in the logic for determining whether an SKE should be
expected or not. In particular only allow an SKE for RSA if its export and
the key size is not allowed. Also fix the ephemeral ciphersuite checks and
add in a missing call to ssl3_check_cert_and_algorithm().
Reviewed-by: NTim Hudson <tjh@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

ssl/statem/statem_clnt.c

@@ -165,7 +165,7 @@
 #endif
 
 static inline int cert_req_allowed(SSL *s);
-static inline int key_exchange_skip_allowed(SSL *s);
+static int key_exchange_expected(SSL *s);
 static int ssl_set_version(SSL *s);
 static int ca_dn_cmp(const X509_NAME *const *a, const X509_NAME *const *b);
 static int ssl_cipher_list_to_bytes(SSL *s, STACK_OF(SSL_CIPHER) *sk,
@@ -190,25 +190,51 @@ static inline int cert_req_allowed(SSL *s)
 }
 
 /*
- * Are we allowed to skip the ServerKeyExchange message?
+ * Should we expect the ServerKeyExchange message or not?
  *
  *  Return values are:
  *  1: Yes
  *  0: No
+ * -1: Error
  */
-static inline int key_exchange_skip_allowed(SSL *s)
+static int key_exchange_expected(SSL *s)
 {
     long alg_k = s->s3->tmp.new_cipher->algorithm_mkey;
 
     /*
      * Can't skip server key exchange if this is an ephemeral
-     * ciphersuite.
+     * ciphersuite or for SRP
      */
-    if (alg_k & (SSL_kDHE | SSL_kECDHE)) {
-        return 0;
+    if (alg_k & (SSL_kDHE | SSL_kECDHE | SSL_kDHEPSK | SSL_kECDHEPSK
+                 | SSL_kSRP)) {
+        return 1;
     }
 
-    return 1;
+    /*
+     * Export ciphersuites may have temporary RSA keys if the public key in the
+     * server certificate is longer than the maximum export strength
+     */
+    if ((alg_k & SSL_kRSA) && SSL_C_IS_EXPORT(s->s3->tmp.new_cipher)) {
+        EVP_PKEY *pkey;
+
+        pkey = X509_get_pubkey(s->session->peer);
+        if (pkey == NULL)
+            return -1;
+
+        /*
+         * If the public key in the certificate is shorter than or equal to the
+         * maximum export strength then a temporary RSA key is not allowed
+         */
+        if (EVP_PKEY_bits(pkey)
+                <= SSL_C_EXPORT_PKEYLENGTH(s->s3->tmp.new_cipher))
+            return 0;
+
+        EVP_PKEY_free(pkey);
+
+        return 1;
+    }
+
+    return 0;
 }
 
 /*
@@ -224,6 +250,7 @@ static inline int key_exchange_skip_allowed(SSL *s)
 int client_read_transition(SSL *s, int mt)
 {
     STATEM *st = &s->statem;
+    int ske_expected;
 
     switch(st->hand_state) {
     case TLS_ST_CW_CLNT_HELLO:
@@ -262,18 +289,24 @@ int client_read_transition(SSL *s, int mt)
                     return 1;
                 }
             } else {
-                if (mt == SSL3_MT_SERVER_KEY_EXCHANGE) {
-                    st->hand_state = TLS_ST_CR_KEY_EXCH;
-                    return 1;
-                } else if (key_exchange_skip_allowed(s)) {
-                    if (mt == SSL3_MT_CERTIFICATE_REQUEST
+                ske_expected = key_exchange_expected(s);
+                if (ske_expected < 0)
+                    return 0;
+                /* SKE is optional for some PSK ciphersuites */
+                if (ske_expected
+                        || ((s->s3->tmp.new_cipher->algorithm_mkey & SSL_PSK)
+                            && mt == SSL3_MT_SERVER_KEY_EXCHANGE)) {
+                    if (mt == SSL3_MT_SERVER_KEY_EXCHANGE) {
+                        st->hand_state = TLS_ST_CR_KEY_EXCH;
+                        return 1;
+                    }
+                } else if (mt == SSL3_MT_CERTIFICATE_REQUEST
                             && cert_req_allowed(s)) {
                         st->hand_state = TLS_ST_CR_CERT_REQ;
                         return 1;
-                    } else if (mt == SSL3_MT_SERVER_DONE) {
+                } else if (mt == SSL3_MT_SERVER_DONE) {
                         st->hand_state = TLS_ST_CR_SRVR_DONE;
                         return 1;
-                    }
                 }
             }
         }
@@ -285,46 +318,35 @@ int client_read_transition(SSL *s, int mt)
                 st->hand_state = TLS_ST_CR_CERT_STATUS;
                 return 1;
             }
-        } else {
+            return 0;
+        }
+        /* Fall through */
+
+    case TLS_ST_CR_CERT_STATUS:
+        ske_expected = key_exchange_expected(s);
+        if (ske_expected < 0)
+            return 0;
+        /* SKE is optional for some PSK ciphersuites */
+        if (ske_expected
+                || ((s->s3->tmp.new_cipher->algorithm_mkey & SSL_PSK)
+                    && mt == SSL3_MT_SERVER_KEY_EXCHANGE)) {
             if (mt == SSL3_MT_SERVER_KEY_EXCHANGE) {
                 st->hand_state = TLS_ST_CR_KEY_EXCH;
                 return 1;
-            } else if (key_exchange_skip_allowed(s)) {
-                if (mt == SSL3_MT_CERTIFICATE_REQUEST && cert_req_allowed(s)) {
-                    st->hand_state = TLS_ST_CR_CERT_REQ;
-                    return 1;
-                } else if (mt == SSL3_MT_SERVER_DONE) {
-                    st->hand_state = TLS_ST_CR_SRVR_DONE;
-                    return 1;
-                }
             }
+            return 0;
         }
-        break;
+        /* Fall through */
 
-    case TLS_ST_CR_CERT_STATUS:
-        if (mt == SSL3_MT_SERVER_KEY_EXCHANGE) {
-            st->hand_state = TLS_ST_CR_KEY_EXCH;
-            return 1;
-        } else if (key_exchange_skip_allowed(s)) {
-            if (mt == SSL3_MT_CERTIFICATE_REQUEST && cert_req_allowed(s)) {
+    case TLS_ST_CR_KEY_EXCH:
+        if (mt == SSL3_MT_CERTIFICATE_REQUEST) {
+            if (cert_req_allowed(s)) {
                 st->hand_state = TLS_ST_CR_CERT_REQ;
                 return 1;
-            } else if (mt == SSL3_MT_SERVER_DONE) {
-                st->hand_state = TLS_ST_CR_SRVR_DONE;
-                return 1;
             }
+            return 0;
         }
-        break;
-
-    case TLS_ST_CR_KEY_EXCH:
-        if (mt == SSL3_MT_CERTIFICATE_REQUEST && cert_req_allowed(s)) {
-            st->hand_state = TLS_ST_CR_CERT_REQ;
-            return 1;
-        } else if (mt == SSL3_MT_SERVER_DONE) {
-            st->hand_state = TLS_ST_CR_SRVR_DONE;
-            return 1;
-        }
-        break;
+        /* Fall through */
 
     case TLS_ST_CR_CERT_REQ:
         if (mt == SSL3_MT_SERVER_DONE) {
@@ -1721,12 +1743,6 @@ enum MSG_PROCESS_RETURN tls_process_key_exchange(SSL *s, PACKET *pkt)
             goto err;
         }
 
-        if (EVP_PKEY_bits(pkey) <= SSL_C_EXPORT_PKEYLENGTH(s->s3->tmp.new_cipher)) {
-            al = SSL_AD_UNEXPECTED_MESSAGE;
-            SSLerr(SSL_F_TLS_PROCESS_KEY_EXCHANGE, SSL_R_UNEXPECTED_MESSAGE);
-            goto f_err;
-        }
-
         s->s3->peer_rsa_tmp = rsa;
         rsa = NULL;
     }
@@ -2312,6 +2328,16 @@ enum MSG_PROCESS_RETURN tls_process_server_done(SSL *s, PACKET *pkt)
     }
 #endif
 
+    /*
+     * at this point we check that we have the required stuff from
+     * the server
+     */
+    if (!ssl3_check_cert_and_algorithm(s)) {
+        ssl3_send_alert(s, SSL3_AL_FATAL, SSL_AD_HANDSHAKE_FAILURE);
+        statem_set_error(s);
+        return MSG_PROCESS_ERROR;
+    }
+
 #ifndef OPENSSL_NO_SCTP
     /* Only applies to renegotiation */
     if (SSL_IS_DTLS(s) && BIO_dgram_is_sctp(SSL_get_wbio(s))