[Openvpn-devel,v3,10/25] dco: periodically check and possibly rotate/delete keys

diff --git a/src/openvpn/dco.c b/src/openvpn/dco.c
index b0dd922a..dfdf10ea 100644
--- a/src/openvpn/dco.c
+++ b/src/openvpn/dco.c
@@ -94,6 +94,128 @@  init_key_dco_bi(struct tls_multi *multi, struct key_state *ks,
                            ciphername);
 }
 
+/**
+ * Find a usable key that is not the primary (i.e. the secondary key)
+ *
+ * @param multi     The TLS struct to retrieve keys from
+ * @param primary   The primary key that should be skipped during the scan
+ *
+ * @return          The secondary key or NULL if none could be found
+ */
+static struct key_state *
+dco_get_secondary_key(struct tls_multi *multi, const struct key_state *primary)
+{
+    for (int i = 0; i < KEY_SCAN_SIZE; ++i)
+    {
+        struct key_state *ks = get_key_scan(multi, i);
+        struct key_ctx_bi *key = &ks->crypto_options.key_ctx_bi;
+
+        if (ks == primary)
+        {
+            continue;
+        }
+
+        if (ks->state >= S_GENERATED_KEYS && ks->authenticated == KS_AUTH_TRUE)
+        {
+            ASSERT(key->initialized);
+            return ks;
+        }
+    }
+
+    return NULL;
+}
+
+void
+dco_update_keys(dco_context_t *dco, struct tls_multi *multi)
+{
+    msg(D_DCO_DEBUG, "%s: peer_id=%d", __func__, multi->peer_id);
+
+    /* this function checks if keys have to be swapped or erased, therefore it
+     * can't do much if we don't have any key installed
+     */
+    if (multi->dco_keys_installed == 0)
+    {
+        return;
+    }
+
+    struct key_state *primary = tls_select_encryption_key(multi);
+    /* no primary key available -> no usable key exists, therefore we should
+     * tell DCO to simply wipe all keys
+     */
+    if (!primary)
+    {
+        msg(D_DCO, "No encryption key found. Purging data channel keys");
+
+        int ret = dco_del_key(dco, multi->peer_id, OVPN_KEY_SLOT_PRIMARY);
+        if (ret < 0)
+        {
+            msg(D_DCO, "Cannot delete primary key during wipe: %s (%d)", strerror(-ret), ret);
+            return;
+        }
+
+        ret = dco_del_key(dco, multi->peer_id, OVPN_KEY_SLOT_SECONDARY);
+        if (ret < 0)
+        {
+            msg(D_DCO, "Cannot delete secondary key during wipe: %s (%d)", strerror(-ret), ret);
+            return;
+        }
+
+        multi->dco_keys_installed = 0;
+        return;
+    }
+
+    /* if we have a primary key, it must have been installed already (keys
+     * are installed upon generation in the TLS code)
+     */
+    ASSERT(primary->dco_status != DCO_NOT_INSTALLED);
+
+    struct key_state *secondary = dco_get_secondary_key(multi, primary);
+    /* the current primary key was installed as secondary in DCO, this means
+     * we have promoted it and we should tell DCO to swap keys
+     */
+    if (primary->dco_status == DCO_INSTALLED_SECONDARY)
+    {
+        msg(D_DCO_DEBUG, "Swapping primary and secondary keys, now: id1=%d id2=%d",
+            primary->key_id, secondary ? secondary->key_id : -1);
+
+        int ret = dco_swap_keys(dco, multi->peer_id);
+        if (ret < 0)
+        {
+            msg(D_DCO, "Cannot swap keys: %s (%d)", strerror(-ret), ret);
+            return;
+        }
+
+        primary->dco_status = DCO_INSTALLED_PRIMARY;
+        if (secondary)
+        {
+            ASSERT(secondary->dco_status == DCO_INSTALLED_PRIMARY);
+            secondary->dco_status = DCO_INSTALLED_SECONDARY;
+        }
+    }
+
+    /* if we have no secondary key anymore, inform DCO about it */
+    if (!secondary && multi->dco_keys_installed == 2)
+    {
+        int ret = dco_del_key(dco, multi->peer_id, OVPN_KEY_SLOT_SECONDARY);
+        if (ret < 0)
+        {
+            msg(D_DCO, "Cannot delete secondary key: %s (%d)", strerror(-ret), ret);
+            return;
+        }
+        multi->dco_keys_installed = 1;
+    }
+
+    /* all keys that are not installed are set to NOT installed */
+    for (int i = 0; i < KEY_SCAN_SIZE; ++i)
+    {
+        struct key_state *ks = get_key_scan(multi, i);
+        if (ks != primary && ks != secondary)
+        {
+            ks->dco_status = DCO_NOT_INSTALLED;
+        }
+    }
+}
+
 static bool
 dco_check_option_conflict_platform(int msglevel, const struct options *o)
 {
diff --git a/src/openvpn/dco.h b/src/openvpn/dco.h
index 1692f5c3..b926e236 100644
--- a/src/openvpn/dco.h
+++ b/src/openvpn/dco.h
@@ -132,6 +132,14 @@  int init_key_dco_bi(struct tls_multi *multi, struct key_state *ks,
                     const struct key2 *key2, int key_direction,
                     const char *ciphername, bool server);
 
+/**
+ * Possibly swap or wipe keys from DCO
+ *
+ * @param dco           DCO device context
+ * @param multi         TLS multi instance
+ */
+void dco_update_keys(dco_context_t *dco, struct tls_multi *multi);
+
 #else /* if defined(ENABLE_DCO) */
 
 typedef void *dco_context_t;
@@ -192,5 +200,11 @@  init_key_dco_bi(struct tls_multi *multi, struct key_state *ks,
     return 0;
 }
 
+static inline void
+dco_update_keys(dco_context_t *dco, struct tls_multi *multi)
+{
+    ASSERT(false);
+}
+
 #endif /* defined(ENABLE_DCO) */
 #endif /* ifndef DCO_H */
diff --git a/src/openvpn/forward.c b/src/openvpn/forward.c
index 28f3c088..38d2683c 100644
--- a/src/openvpn/forward.c
+++ b/src/openvpn/forward.c
@@ -41,6 +41,7 @@ 
 #include "dhcp.h"
 #include "common.h"
 #include "ssl_verify.h"
+#include "dco.h"
 
 #include "memdbg.h"
 
@@ -140,6 +141,18 @@  context_reschedule_sec(struct context *c, int sec)
     }
 }
 
+void
+check_dco_key_status(struct context *c)
+{
+    /* DCO context is not yet initialised or enabled */
+    if (!dco_enabled(&c->options))
+    {
+        return;
+    }
+
+    dco_update_keys(&c->c1.tuntap->dco, c->c2.tls_multi);
+}
+
 /*
  * In TLS mode, let TLS level respond to any control-channel
  * packets which were received, or prepare any packets for
@@ -182,6 +195,12 @@  check_tls(struct context *c)
 
     interval_schedule_wakeup(&c->c2.tmp_int, &wakeup);
 
+    /* Our current code has no good hooks in the TLS machinery to update
+     * DCO keys. So we check the key status after the whole TLS machinery
+     * has been completed and potentially update them
+     */
+    check_dco_key_status(c);
+
     if (wakeup)
     {
         context_reschedule_sec(c, wakeup);