From 31d5c854198ed91fc2bd0b9fb87ed0dcd5a40eb6 Mon Sep 17 00:00:00 2001

From: Greg Hudson <ghudson@mit.edu>

Date: Thu, 24 Aug 2017 16:00:33 -0400

Subject: [PATCH] Limit ticket lifetime to 2^31-1 seconds

Although timestamps above 2^31-1 are now valid, intervals exceeding

2^31-1 seconds may be treated incorrectly by comparison operations.

The initially computed interval in kdc_get_ticket_endtime() could be

negative if the requested end time is far in the future, causing the

function to yield an incorrect result.  (With the new larger value of

kdc_infinity, this could specifically happen if a KDC-REQ contains a

zero till field.)  Cap the interval at the maximum valid value.

Reported by Weijun Wang.

Avoid delta comparisons in favor of timestamp comparions in

krb5int_validate_times(), ksu's krb5_check_exp(), and clockskew

checks.

Also use a y2038-safe timestamp comparison in set_request_times() when

comparing the requested renewable end time to the requested ticket end

time.

ticket: 8352

(cherry picked from commit 54e58755368b58ba5894a14c1d02626da42d8003)

---

 src/clients/ksu/ccache.c       | 2 +-

 src/include/k5-int.h           | 7 +++++++

 src/kdc/kdc_util.c             | 7 ++++++-

 src/kdc/replay.c               | 2 +-

 src/kdc/t_replay.c             | 2 +-

 src/lib/krb5/krb/gc_via_tkt.c  | 4 ++--

 src/lib/krb5/krb/get_in_tkt.c  | 6 +++---

 src/lib/krb5/krb/int-proto.h   | 3 ---

 src/lib/krb5/krb/valid_times.c | 4 ++--

 src/lib/krb5/os/timeofday.c    | 2 +-

 10 files changed, 24 insertions(+), 15 deletions(-)

diff --git a/src/clients/ksu/ccache.c b/src/clients/ksu/ccache.c

index 236313b7b..2a99521d4 100644

--- a/src/clients/ksu/ccache.c

+++ b/src/clients/ksu/ccache.c

@@ -282,7 +282,7 @@ krb5_error_code krb5_check_exp(context, tkt_time)

     }

-    if (ts_delta(currenttime, tkt_time.endtime) > context->clockskew) {

+    if (ts_after(currenttime, ts_incr(tkt_time.endtime, context->clockskew))) {

         retval = KRB5KRB_AP_ERR_TKT_EXPIRED ;

         return retval;

     }

diff --git a/src/include/k5-int.h b/src/include/k5-int.h

index 39ffb9568..e31004a7c 100644

--- a/src/include/k5-int.h

+++ b/src/include/k5-int.h

@@ -2386,6 +2386,13 @@ ts_after(krb5_timestamp a, krb5_timestamp b)

     return (uint32_t)a > (uint32_t)b;

 }

+/* Return true if a and b are within d seconds. */

+static inline krb5_boolean

+ts_within(krb5_timestamp a, krb5_timestamp b, krb5_deltat d)

+{

+    return !ts_after(a, ts_incr(b, d)) && !ts_after(b, ts_incr(a, d));

+}

+

 krb5_error_code KRB5_CALLCONV

 krb5_get_credentials_for_user(krb5_context context, krb5_flags options,

                               krb5_ccache ccache,

diff --git a/src/kdc/kdc_util.c b/src/kdc/kdc_util.c

index 5455e2a67..770163b94 100644

--- a/src/kdc/kdc_util.c

+++ b/src/kdc/kdc_util.c

@@ -1759,14 +1759,19 @@ kdc_get_ticket_endtime(kdc_realm_t *kdc_active_realm,

                        krb5_db_entry *server,

                        krb5_timestamp *out_endtime)

 {

-    krb5_timestamp until, life;

+    krb5_timestamp until;

+    krb5_deltat life;

     if (till == 0)

         till = kdc_infinity;

     until = ts_min(till, endtime);

+    /* Determine the requested lifetime, capped at the maximum valid time

+     * interval. */

     life = ts_delta(until, starttime);

+    if (ts_after(until, starttime) && life < 0)

+        life = INT32_MAX;

     if (client != NULL && client->max_life != 0)

         life = min(life, client->max_life);

diff --git a/src/kdc/replay.c b/src/kdc/replay.c

index fab39cf88..caca783bf 100644

--- a/src/kdc/replay.c

+++ b/src/kdc/replay.c

@@ -61,7 +61,7 @@ static size_t total_size = 0;

 static krb5_ui_4 seed;

 #define STALE_TIME      (2*60)            /* two minutes */

-#define STALE(ptr, now) (labs(ts_delta((ptr)->timein, now)) >= STALE_TIME)

+#define STALE(ptr, now) (ts_after(now, ts_incr((ptr)->timein, STALE_TIME)))

 /* Return x rotated to the left by r bits. */

 static inline krb5_ui_4

diff --git a/src/kdc/t_replay.c b/src/kdc/t_replay.c

index 1442e0e8c..bb7e2faff 100644

--- a/src/kdc/t_replay.c

+++ b/src/kdc/t_replay.c

@@ -903,7 +903,7 @@ test_kdc_insert_lookaside_cache_expire(void **state)

     assert_non_null(e);

     e->num_hits = 5;

-    time_return(STALE_TIME, 0);

+    time_return(STALE_TIME + 1, 0);

     kdc_insert_lookaside(context, &req2, NULL);

     assert_null(K5_LIST_FIRST(&hash_table[req_hash1]));

diff --git a/src/lib/krb5/krb/gc_via_tkt.c b/src/lib/krb5/krb/gc_via_tkt.c

index cf1ea361f..5b9bb9573 100644

--- a/src/lib/krb5/krb/gc_via_tkt.c

+++ b/src/lib/krb5/krb/gc_via_tkt.c

@@ -306,8 +306,8 @@ krb5int_process_tgs_reply(krb5_context context,

         goto cleanup;

     if (!in_cred->times.starttime &&

-        !in_clock_skew(context, dec_rep->enc_part2->times.starttime,

-                       timestamp)) {

+        !ts_within(dec_rep->enc_part2->times.starttime, timestamp,

+                   context->clockskew)) {

         retval = KRB5_KDCREP_SKEW;

         goto cleanup;

     }

diff --git a/src/lib/krb5/krb/get_in_tkt.c b/src/lib/krb5/krb/get_in_tkt.c

index 7178bd87b..ed15550f0 100644

--- a/src/lib/krb5/krb/get_in_tkt.c

+++ b/src/lib/krb5/krb/get_in_tkt.c

@@ -269,8 +269,8 @@ verify_as_reply(krb5_context            context,

             return retval;

     } else {

         if ((request->from == 0) &&

-            !in_clock_skew(context, as_reply->enc_part2->times.starttime,

-                           time_now))

+            !ts_within(as_reply->enc_part2->times.starttime, time_now,

+                       context->clockskew))

             return (KRB5_KDCREP_SKEW);

     }

     return 0;

@@ -781,7 +781,7 @@ set_request_times(krb5_context context, krb5_init_creds_context ctx)

     if (ctx->renew_life > 0) {

         /* Don't ask for a smaller renewable time than the lifetime. */

         ctx->request->rtime = ts_incr(from, ctx->renew_life);

-        if (ctx->request->rtime < ctx->request->till)

+        if (ts_after(ctx->request->till, ctx->request->rtime))

             ctx->request->rtime = ctx->request->till;

         ctx->request->kdc_options &= ~KDC_OPT_RENEWABLE_OK;

     } else {

diff --git a/src/lib/krb5/krb/int-proto.h b/src/lib/krb5/krb/int-proto.h

index 48bd9f8f7..9c746d05b 100644

--- a/src/lib/krb5/krb/int-proto.h

+++ b/src/lib/krb5/krb/int-proto.h

@@ -83,9 +83,6 @@ krb5int_construct_matching_creds(krb5_context context, krb5_flags options,

                                  krb5_creds *in_creds, krb5_creds *mcreds,

                                  krb5_flags *fields);

-#define in_clock_skew(context, date, now)               \

-    (labs(ts_delta(date, now)) < (context)->clockskew)

-

 #define IS_TGS_PRINC(p) ((p)->length == 2 &&                            \

                          data_eq_string((p)->data[0], KRB5_TGS_NAME))

diff --git a/src/lib/krb5/krb/valid_times.c b/src/lib/krb5/krb/valid_times.c

index 9e509b2dd..294761a88 100644

--- a/src/lib/krb5/krb/valid_times.c

+++ b/src/lib/krb5/krb/valid_times.c

@@ -47,10 +47,10 @@ krb5int_validate_times(krb5_context context, krb5_ticket_times *times)

     else

         starttime = times->authtime;

-    if (ts_delta(starttime, currenttime) > context->clockskew)

+    if (ts_after(starttime, ts_incr(currenttime, context->clockskew)))

         return KRB5KRB_AP_ERR_TKT_NYV;  /* ticket not yet valid */

-    if (ts_delta(currenttime, times->endtime) > context->clockskew)

+    if (ts_after(currenttime, ts_incr(times->endtime, context->clockskew)))

         return KRB5KRB_AP_ERR_TKT_EXPIRED; /* ticket expired */

     return 0;

diff --git a/src/lib/krb5/os/timeofday.c b/src/lib/krb5/os/timeofday.c

index 887f24c22..d4e36b1c7 100644

--- a/src/lib/krb5/os/timeofday.c

+++ b/src/lib/krb5/os/timeofday.c

@@ -60,7 +60,7 @@ krb5_check_clockskew(krb5_context context, krb5_timestamp date)

     retval = krb5_timeofday(context, &currenttime);

     if (retval)

         return retval;

-    if (labs(ts_delta(date, currenttime)) >= context->clockskew)

+    if (!ts_within(date, currenttime, context->clockskew))

         return KRB5KRB_AP_ERR_SKEW;

     return 0;