Repair EAP-FAST session resumption

EAP-FAST session resumption relies on handshake message lookahead
to determine server intentions. Commits
980bc1ec6114f5511b20c2e6ca741e61a39b99d6
and
7b3ba508af5c86afe43e28174aa3c53a0a24f4d9
removed the lookahead so broke session resumption.

This change partially reverts the commits and brings the lookahead back
in reduced capacity for TLS + EAP-FAST only. Since EAP-FAST does not
support regular session tickets, the lookahead now only checks for a
Finished message.

Regular handshakes are unaffected by this change.

Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Matt Caswell <matt@openssl.org>

2 files changed, 99 insertions, 18 deletions

diff --git a/ssl/s3_clnt.c b/ssl/s3_clnt.c
index 697a3b4f6a..3eb67ef17b 100644
--- a/ssl/s3_clnt.c
+++ b/ssl/s3_clnt.c
@@ -165,6 +165,9 @@
 #endif
 
 static int ca_dn_cmp(const X509_NAME *const *a, const X509_NAME *const *b);
+#ifndef OPENSSL_NO_TLSEXT
+static int ssl3_check_finished(SSL *s);
+#endif
 
 #ifndef OPENSSL_NO_SSL3_METHOD
 static const SSL_METHOD *ssl3_get_client_method(int ver)
@@ -321,6 +324,18 @@ int ssl3_connect(SSL *s)
             break;
         case SSL3_ST_CR_CERT_A:
         case SSL3_ST_CR_CERT_B:
+#ifndef OPENSSL_NO_TLSEXT
+            /* Noop (ret = 0) for everything but EAP-FAST. */
+            ret = ssl3_check_finished(s);
+            if (ret < 0)
+                goto end;
+            if (ret == 1) {
+                s->hit = 1;
+                s->state = SSL3_ST_CR_FINISHED_A;
+                s->init_num = 0;
+                break;
+            }
+#endif
             /* Check if it is anon DH/ECDH, SRP auth */
             /* or PSK */
             if (!
@@ -557,7 +572,8 @@ int ssl3_connect(SSL *s)
 
         case SSL3_ST_CR_FINISHED_A:
         case SSL3_ST_CR_FINISHED_B:
-            s->s3->flags |= SSL3_FLAGS_CCS_OK;
+            if (!s->s3->change_cipher_spec)
+                s->s3->flags |= SSL3_FLAGS_CCS_OK;
             ret = ssl3_get_finished(s, SSL3_ST_CR_FINISHED_A,
                                     SSL3_ST_CR_FINISHED_B);
             if (ret <= 0)
@@ -663,9 +679,17 @@ int ssl3_client_hello(SSL *s)
     buf = (unsigned char *)s->init_buf->data;
     if (s->state == SSL3_ST_CW_CLNT_HELLO_A) {
         SSL_SESSION *sess = s->session;
-        if ((sess == NULL) ||
-            (sess->ssl_version != s->version) ||
-            !sess->session_id_length || (sess->not_resumable)) {
+        if ((sess == NULL) || (sess->ssl_version != s->version) ||
+#ifdef OPENSSL_NO_TLSEXT
+            !sess->session_id_length ||
+#else
+            /*
+             * In the case of EAP-FAST, we can have a pre-shared
+             * "ticket" without a session ID.
+             */
+            (!sess->session_id_length && !sess->tlsext_tick) ||
+#endif
+            (sess->not_resumable)) {
             if (!ssl_get_new_session(s, 0))
                 goto err;
         }
@@ -953,10 +977,19 @@ int ssl3_get_server_hello(SSL *s)
     }
 #ifndef OPENSSL_NO_TLSEXT
     /*
-     * check if we want to resume the session based on external pre-shared
-     * secret
+     * Check if we can resume the session based on external pre-shared secret.
+     * EAP-FAST (RFC 4851) supports two types of session resumption.
+     * Resumption based on server-side state works with session IDs.
+     * Resumption based on pre-shared Protected Access Credentials (PACs)
+     * works by overriding the SessionTicket extension at the application
+     * layer, and does not send a session ID. (We do not know whether EAP-FAST
+     * servers would honour the session ID.) Therefore, the session ID alone
+     * is not a reliable indicator of session resumption, so we first check if
+     * we can resume, and later peek at the next handshake message to see if the
+     * server wants to resume.
      */
-    if (s->version >= TLS1_VERSION && s->tls_session_secret_cb) {
+    if (s->version >= TLS1_VERSION && s->tls_session_secret_cb &&
+        s->session->tlsext_tick) {
         SSL_CIPHER *pref_cipher = NULL;
         s->session->master_key_length = sizeof(s->session->master_key);
         if (s->tls_session_secret_cb(s, s->session->master_key,
@@ -965,12 +998,15 @@ int ssl3_get_server_hello(SSL *s)
                                      s->tls_session_secret_cb_arg)) {
             s->session->cipher = pref_cipher ?
                 pref_cipher : ssl_get_cipher_by_char(s, p + j);
-            s->hit = 1;
+        } else {
+            SSLerr(SSL_F_SSL3_GET_SERVER_HELLO, ERR_R_INTERNAL_ERROR);
+            al = SSL_AD_INTERNAL_ERROR;
+            goto f_err;
         }
     }
 #endif                          /* OPENSSL_NO_TLSEXT */
 
-    if (!s->hit && j != 0 && j == s->session->session_id_length
+    if (j != 0 && j == s->session->session_id_length
         && memcmp(p, s->session->session_id, j) == 0) {
         if (s->sid_ctx_length != s->session->sid_ctx_length
             || memcmp(s->session->sid_ctx, s->sid_ctx, s->sid_ctx_length)) {
@@ -981,12 +1017,13 @@ int ssl3_get_server_hello(SSL *s)
             goto f_err;
         }
         s->hit = 1;
-    }
-    /* a miss or crap from the other end */
-    if (!s->hit) {
+    } else {
         /*
-         * If we were trying for session-id reuse, make a new SSL_SESSION so
-         * we don't stuff up other people
+         * If we were trying for session-id reuse but the server
+         * didn't echo the ID, make a new SSL_SESSION.
+         * In the case of EAP-FAST and PAC, we do not send a session ID,
+         * so the PAC-based session secret is always preserved. It'll be
+         * overwritten if the server refuses resumption.
          */
         if (s->session->session_id_length > 0) {
             if (!ssl_get_new_session(s, 0)) {
@@ -3473,13 +3510,56 @@ int ssl3_check_cert_and_algorithm(SSL *s)
     return (0);
 }
 
+#ifndef OPENSSL_NO_TLSEXT
 /*
- * Check to see if handshake is full or resumed. Usually this is just a case
- * of checking to see if a cache hit has occurred. In the case of session
- * tickets we have to check the next message to be sure.
+ * Normally, we can tell if the server is resuming the session from
+ * the session ID. EAP-FAST (RFC 4851), however, relies on the next server
+ * message after the ServerHello to determine if the server is resuming.
+ * Therefore, we allow EAP-FAST to peek ahead.
+ * ssl3_check_finished returns 1 if we are resuming from an external
+ * pre-shared secret, we have a "ticket" and the next server handshake message
+ * is Finished; and 0 otherwise. It returns -1 upon an error.
  */
+static int ssl3_check_finished(SSL *s)
+{
+    int ok = 0;
+
+    if (s->version < TLS1_VERSION || !s->tls_session_secret_cb ||
+        !s->session->tlsext_tick)
+        return 0;
+
+    /* Need to permit this temporarily, in case the next message is Finished. */
+    s->s3->flags |= SSL3_FLAGS_CCS_OK;
+    /*
+     * This function is called when we might get a Certificate message instead,
+     * so permit appropriate message length.
+     * We ignore the return value as we're only interested in the message type
+     * and not its length.
+     */
+    s->method->ssl_get_message(s,
+                               SSL3_ST_CR_CERT_A,
+                               SSL3_ST_CR_CERT_B,
+                               -1, s->max_cert_list, &ok);
+    s->s3->flags &= ~SSL3_FLAGS_CCS_OK;
+
+    if (!ok)
+        return -1;
+
+    s->s3->tmp.reuse_message = 1;
+
+    if (s->s3->tmp.message_type == SSL3_MT_FINISHED)
+        return 1;
+
+    /* If we're not done, then the CCS arrived early and we should bail. */
+    if (s->s3->change_cipher_spec) {
+        SSLerr(SSL_F_SSL3_CHECK_FINISHED, SSL_R_CCS_RECEIVED_EARLY);
+        ssl3_send_alert(s, SSL3_AL_FATAL, SSL_AD_UNEXPECTED_MESSAGE);
+        return -1;
+    }
+
+    return 0;
+}
 
-#ifndef OPENSSL_NO_TLSEXT
 # ifndef OPENSSL_NO_NEXTPROTONEG
 int ssl3_send_next_proto(SSL *s)
 {
diff --git a/ssl/ssl_err.c b/ssl/ssl_err.c
index 5792906744..5c40b49394 100644
--- a/ssl/ssl_err.c
+++ b/ssl/ssl_err.c
@@ -126,6 +126,7 @@ static ERR_STRING_DATA SSL_str_functs[] = {
     {ERR_FUNC(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM),
      "ssl3_check_cert_and_algorithm"},
     {ERR_FUNC(SSL_F_SSL3_CHECK_CLIENT_HELLO), "ssl3_check_client_hello"},
+    {ERR_FUNC(SSL_F_SSL3_CHECK_FINISHED), "SSL3_CHECK_FINISHED"},
     {ERR_FUNC(SSL_F_SSL3_CLIENT_HELLO), "ssl3_client_hello"},
     {ERR_FUNC(SSL_F_SSL3_CONNECT), "ssl3_connect"},
     {ERR_FUNC(SSL_F_SSL3_CTRL), "ssl3_ctrl"},