revocation: Ignore CRLs that are not yet valid

Using such CRLs can be a problem if the clock on the host doing the
revocation check is trailing behind that of the host issuing CRLs in
scenarios where expired certificates are removed from CRLs.  As revoked
certificates that expired will then not be part of new CRLs a host with
trailing clock might still accept such a certificate if it is still
valid according to its system clock but is not contained anymore in the
not yet valid CRL.

diff --git a/src/libstrongswan/plugins/revocation/revocation_validator.c b/src/libstrongswan/plugins/revocation/revocation_validator.c
index 0611be43e574b3963dbba5c6ef5892e05b9d8cf8..0e3ab2dfd205ff6503b7115e9bf69acdeb29ee78 100644 (file)
--- a/src/libstrongswan/plugins/revocation/revocation_validator.c
+++ b/src/libstrongswan/plugins/revocation/revocation_validator.c
@@ -1,8 +1,9 @@
 /*
+ * Copyright (C) 2015-2018 Tobias Brunner
  * Copyright (C) 2010 Martin Willi
  * Copyright (C) 2010 revosec AG
  * Copyright (C) 2009 Andreas Steffen
- * Hochschule fuer Technik Rapperswil
+ * HSR Hochschule fuer Technik Rapperswil
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the
@@ -15,6 +16,8 @@
  * for more details.
  */
 
+#include <time.h>
+
 #include "revocation_validator.h"
 
 #include <utils/debug.h>
@@ -417,11 +420,11 @@ static bool verify_crl(certificate_t *crl)
 /**
  * Report the given CRL's validity and cache it if valid and requested
  */
-static bool is_crl_valid(certificate_t *crl, bool cache)
+static bool is_crl_valid(certificate_t *crl, time_t now, bool cache)
 {
        time_t valid_until;
 
-       if (crl->get_validity(crl, NULL, NULL, &valid_until))
+       if (crl->get_validity(crl, &now, NULL, &valid_until))
        {
                DBG1(DBG_CFG, "  crl is valid: until %T", &valid_until, FALSE);
                if (cache)
@@ -434,6 +437,25 @@ static bool is_crl_valid(certificate_t *crl, bool cache)
        return FALSE;
 }
 
+/**
+ * Check if the CRL should be used yet
+ */
+static bool is_crl_not_valid_yet(certificate_t *crl, time_t now)
+{
+       time_t this_update;
+
+       if (!crl->get_validity(crl, &now, &this_update, NULL))
+       {
+               if (this_update > now)
+               {
+                       DBG1(DBG_CFG, "  crl is not valid: until %T", &this_update, FALSE);
+                       return TRUE;
+               }
+               /* we accept stale CRLs */
+       }
+       return FALSE;
+}
+
 /**
  * Get the better of two CRLs, and check for usable CRL info
  */
@@ -442,7 +464,7 @@ static certificate_t *get_better_crl(certificate_t *cand, certificate_t *best,
                                        bool cache, crl_t *base)
 {
        enumerator_t *enumerator;
-       time_t revocation;
+       time_t now, revocation;
        crl_reason_t reason;
        chunk_t subject_serial, serial;
        crl_t *crl = (crl_t*)cand;
@@ -472,6 +494,12 @@ static certificate_t *get_better_crl(certificate_t *cand, certificate_t *best,
                cand->destroy(cand);
                return best;
        }
+       now = time(NULL);
+       if (is_crl_not_valid_yet(cand, now))
+       {
+               cand->destroy(cand);
+               return best;
+       }
 
        subject_serial = chunk_skip_zero(subject->get_serial(subject));
        enumerator = crl->create_enumerator(crl);
@@ -488,7 +516,7 @@ static certificate_t *get_better_crl(certificate_t *cand, certificate_t *best,
                                /* if the cert is on hold, a newer CRL might not contain it */
                                *valid = VALIDATION_ON_HOLD;
                        }
-                       is_crl_valid(cand, cache);
+                       is_crl_valid(cand, now, cache);
                        DBG1(DBG_CFG, "certificate was revoked on %T, reason: %N",
                                 &revocation, TRUE, crl_reason_names, reason);
                        enumerator->destroy(enumerator);
@@ -503,7 +531,7 @@ static certificate_t *get_better_crl(certificate_t *cand, certificate_t *best,
        {
                DESTROY_IF(best);
                best = cand;
-               if (is_crl_valid(best, cache))
+               if (is_crl_valid(best, now, cache))
                {
                        *valid = VALIDATION_GOOD;
                }