[Openvpn-devel,6/7] Introduce S_GENERATED_KEYS state and generate keys only when authenticated

Message ID 20210422151724.2132573-6-arne@rfc2549.org
State Under Review
Delegated to: Antonio Quartulli
Headers show
Series
  • [Openvpn-devel,1/7] Move tls_select_primary_key into its own function
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Commit Message

Arne Schwabe April 22, 2021, 3:17 p.m.
Since generating data channel does not happen when we have reach the
S_ACTIVE/S_GOT_KEY state anymore like it used to be before NCP, the
state that data channel keys deserves its own state in the state machine.

The changes done by this commit are rather intrusive since they
move the key generation to a completely different place and also
rely on the state machine to decide if keys should be
generated rather than on the complicated conditions that were
implemented in the key_method_2_write/read methods.

A (intended) side effect of this change is that sessions that
are still in deferred state (ks->authenticated == KS_DEFERRED)
will not have data channel keys generated. This avoids corner
cases where not fully authenticated sessions might leak data.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
---
 src/openvpn/forward.h    |  2 +-
 src/openvpn/init.c       |  1 +
 src/openvpn/ssl.c        | 88 +++++++++++++++++-----------------------
 src/openvpn/ssl.h        | 10 +++++
 src/openvpn/ssl_common.h |  9 +++-
 5 files changed, 57 insertions(+), 53 deletions(-)

Patch

diff --git a/src/openvpn/forward.h b/src/openvpn/forward.h
index 3461e6422..b8760099e 100644
--- a/src/openvpn/forward.h
+++ b/src/openvpn/forward.h
@@ -450,7 +450,7 @@  connection_established(struct context *c)
 {
     if (c->c2.tls_multi)
     {
-        return c->c2.tls_multi->multi_state >= CAS_CONNECT_DONE;
+        return c->c2.tls_multi->multi_state >= CAS_WAITING_OPTIONS_IMPORT;
     }
     else
     {
diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index 8a5c7bc55..d7e71a497 100644
--- a/src/openvpn/init.c
+++ b/src/openvpn/init.c
@@ -2202,6 +2202,7 @@  do_up(struct context *c, bool pulled_options, unsigned int option_types_found)
         }
 
         c->c2.do_up_ran = true;
+        c->c2.tls_multi->multi_state = CAS_CONNECT_DONE;
     }
     return true;
 }
diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
index 4bb395039..a7e0c9148 100644
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -788,6 +788,9 @@  state_name(int state)
         case S_ERROR:
             return "S_ERROR";
 
+        case S_GENERATED_KEYS:
+            return "S_GENERATED_KEYS";
+
         default:
             return "S_???";
     }
@@ -1840,13 +1843,13 @@  key_ctx_update_implicit_iv(struct key_ctx *ctx, uint8_t *key, size_t key_len)
  * This erases the source material used to generate the data channel keys, and
  * can thus be called only once per session.
  */
-static bool
+bool
 tls_session_generate_data_channel_keys(struct tls_session *session)
 {
     bool ret = false;
     struct key_state *ks = &session->key[KS_PRIMARY];   /* primary key */
 
-    if (ks->authenticated == KS_AUTH_FALSE)
+    if (ks->authenticated <= KS_AUTH_FALSE)
     {
         msg(D_TLS_ERRORS, "TLS Error: key_state not authenticated");
         goto cleanup;
@@ -1862,6 +1865,9 @@  tls_session_generate_data_channel_keys(struct tls_session *session)
     tls_limit_reneg_bytes(session->opt->key_type.cipher,
                           &session->opt->renegotiate_bytes);
 
+    /* set the state of the keys for the session to generated */
+    ks->state = S_GENERATED_KEYS;
+
     ret = true;
 cleanup:
     secure_memzero(ks->key_src, sizeof(*ks->key_src));
@@ -2375,30 +2381,6 @@  key_method_2_write(struct buffer *buf, struct tls_multi *multi, struct tls_sessi
         goto error;
     }
 
-    /*
-     * Generate tunnel keys if we're a TLS server.
-     *
-     * If we're a p2mp server to allow NCP, the first key
-     * generation is postponed until after the connect script finished and the
-     * NCP options can be processed. Since that always happens at after connect
-     * script options are available the CAS_CONNECT_DONE status is identical to
-     * NCP options are processed and do not wait for NCP being finished.
-     */
-    if (ks->authenticated > KS_AUTH_FALSE && session->opt->mode == MODE_SERVER
-        && (multi->multi_state >= CAS_CONNECT_DONE || ks->key_id > 0))
-    {
-        /* if key_id >= 1, is a renegotiation, so we use the already established
-         * parameters and do not need to delay anything. */
-
-        /* key-id == 0 and multi_state >= CAS_CONNECT_DONE is a special case of
-         * the server reusing the session of a reconnecting client. */
-        if (!tls_session_generate_data_channel_keys(session))
-        {
-            msg(D_TLS_ERRORS, "TLS Error: server generate_key_expansion failed");
-            goto error;
-        }
-    }
-
     return true;
 
 error:
@@ -2598,21 +2580,7 @@  key_method_2_read(struct buffer *buf, struct tls_multi *multi, struct tls_sessio
 
         setenv_del(session->opt->es, "exported_keying_material");
     }
-
-    /*
-     * Generate tunnel keys if we're a client.
-     * If --pull is enabled, the first key generation is postponed until after the
-     * pull/push, so we can process pushed cipher directives.
-     */
-    if (!session->opt->server && (!session->opt->pull || ks->key_id > 0))
-    {
-        if (!tls_session_generate_data_channel_keys(session))
-        {
-            msg(D_TLS_ERRORS, "TLS Error: client generate_key_expansion failed");
-            goto error;
-        }
-    }
-
+    
     gc_free(&gc);
     return true;
 
@@ -2814,7 +2782,7 @@  tls_process(struct tls_multi *multi,
                     else
                     {
                         /* Skip the connect script related states */
-                        multi->multi_state = CAS_CONNECT_DONE;
+                        multi->multi_state = CAS_WAITING_OPTIONS_IMPORT;
                     }
                 }
 
@@ -3137,6 +3105,27 @@  tls_multi_process(struct tls_multi *multi,
 
     /* If we have successfully authenticated and are still waiting for the authentication to finish
      * move the state machine for the multi context forward */
+
+    if (multi->multi_state >= CAS_CONNECT_DONE)
+    {
+        for (int i = 0; i < TM_SIZE; ++i)
+        {
+            struct tls_session *session = &multi->session[i];
+            struct key_state *ks = &session->key[KS_PRIMARY];
+
+            if (ks->state == S_ACTIVE && ks->authenticated == KS_AUTH_TRUE)
+            {
+                /* This will ks->state from S_ACTIVE to S_GENERATED_KEYS */
+                if (!tls_session_generate_data_channel_keys(session))
+                {
+                    msg(D_TLS_ERRORS, "TLS Error: generate_key_expansion failed");
+                    ks->authenticated = KS_AUTH_FALSE;
+                    ks->state = S_ERROR;
+                }
+            }
+        }
+    }
+
     if (multi->multi_state == CAS_WAITING_AUTH && tas == TLS_AUTHENTICATION_SUCCEEDED)
     {
         multi->multi_state = CAS_PENDING;
@@ -3245,11 +3234,10 @@  handle_data_channel_packet(struct tls_multi *multi,
          * passive side is the server which only listens for the connections, the
          * active side is the client which initiates connections).
          */
-        if (TLS_AUTHENTICATED(multi, ks)
-            && key_id == ks->key_id
-            && (ks->authenticated == KS_AUTH_TRUE)
+        if (ks->state >= S_GENERATED_KEYS  && key_id == ks->key_id
             && (floated || link_socket_actual_match(from, &ks->remote_addr)))
         {
+            ASSERT(ks->authenticated == KS_AUTH_TRUE);
             if (!ks->crypto_options.key_ctx_bi.initialized)
             {
                 msg(D_MULTI_DROPPED,
@@ -3571,8 +3559,7 @@  tls_pre_decrypt(struct tls_multi *multi,
         /*
          * Remote is requesting a key renegotiation
          */
-        if (op == P_CONTROL_SOFT_RESET_V1
-            && TLS_AUTHENTICATED(multi, ks))
+        if (op == P_CONTROL_SOFT_RESET_V1 && TLS_AUTHENTICATED(multi, ks))
         {
             if (!read_control_auth(buf, &session->tls_wrap, from,
                                    session->opt))
@@ -3833,10 +3820,11 @@  struct key_state *tls_select_encryption_key(struct tls_multi *multi)
     for (int i = 0; i < KEY_SCAN_SIZE; ++i)
     {
         struct key_state *ks = get_key_scan(multi, i);
-        if (ks->state >= S_ACTIVE
-            && ks->authenticated == KS_AUTH_TRUE
-            && ks->crypto_options.key_ctx_bi.initialized)
+        if (ks->state >= S_GENERATED_KEYS)
         {
+            ASSERT(ks->authenticated == KS_AUTH_TRUE);
+            ASSERT(ks->crypto_options.key_ctx_bi.initialized);
+
             if (!ks_select)
             {
                 ks_select = ks;
diff --git a/src/openvpn/ssl.h b/src/openvpn/ssl.h
index 2791143f6..18a11bbdf 100644
--- a/src/openvpn/ssl.h
+++ b/src/openvpn/ssl.h
@@ -615,4 +615,14 @@  show_available_tls_ciphers(const char *cipher_list,
                            const char *cipher_list_tls13,
                            const char *tls_cert_profile);
 
+
+/**
+ * Generate data channel keys for the supplied TLS session.
+ *
+ * This erases the source material used to generate the data channel keys, and
+ * can thus be called only once per session.
+ */
+bool
+tls_session_generate_data_channel_keys(struct tls_session *session);
+
 #endif /* ifndef OPENVPN_SSL_H */
diff --git a/src/openvpn/ssl_common.h b/src/openvpn/ssl_common.h
index 01f00950e..89312cc88 100644
--- a/src/openvpn/ssl_common.h
+++ b/src/openvpn/ssl_common.h
@@ -64,7 +64,8 @@ 
  *      material.
  *   -# \c S_GOT_KEY, have received remote part of \c key_source2 random
  *      material.
- *   -# \c S_ACTIVE, normal operation
+ *   -# \c S_ACTIVE, control channel successfully established
+ *   -# \c S_GENERATED_KEYS, the
  *
  * Servers follow the same order, except for \c S_SENT_KEY and \c
  * S_GOT_KEY being reversed, because the server first receives the
@@ -92,7 +93,10 @@ 
 #define S_ACTIVE          6     /**< Operational \c key_state state
                                  *   immediately after negotiation has
                                  *   completed while still within the
-                                 *   handshake window. */
+                                 *   handshake window, deferred auth, client
+                                 *   connect and can still
+                                 *   be pending. */
+#define S_GENERATED_KEYS  7     /**< The data channel keys have been generated */
 /* Note that earlier versions also had a S_OP_NORMAL state that was
  * virtually identical with S_ACTIVE and the code still assumes everything
  * >= S_ACTIVE to be fully operational */
@@ -517,6 +521,7 @@  enum multi_status {
     CAS_PENDING_DEFERRED,
     CAS_PENDING_DEFERRED_PARTIAL,   /**< at least handler succeeded, no result yet*/
     CAS_FAILED,
+    CAS_WAITING_OPTIONS_IMPORT,     /**< client with pull or p2p waiting for first time options import */
     CAS_CONNECT_DONE,
 };