From: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Date: Mon, 22 Mar 2021 11:51:47 +0000 (+0100)
Subject: shared/calendarspec: when mktime() moves us backwards, jump forward
X-Git-Tag: v248-2~36^2
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=129cb6e249bef30dc33e08f98f0b27a6de976f6f;p=thirdparty%2Fsystemd.git

shared/calendarspec: when mktime() moves us backwards, jump forward

When trying to calculate the next firing of 'Sun *-*-* 01:00:00', we'd fall
into an infinite loop, because mktime() moves us "backwards":

Before this patch:
tm_within_bounds: good=0 2021-03-29 01:00:00 → 2021-03-29 00:00:00
tm_within_bounds: good=0 2021-03-29 01:00:00 → 2021-03-29 00:00:00
tm_within_bounds: good=0 2021-03-29 01:00:00 → 2021-03-29 00:00:00
...

We rely on mktime() normalizing the time. The man page does not say that it'll
move the time forward, but our algorithm relies on this. So let's catch this
case explicitly.

With this patch:
$ TZ=Europe/Dublin faketime 2021-03-21 build/systemd-analyze calendar --iterations=5 'Sun *-*-* 01:00:00'
Normalized form: Sun *-*-* 01:00:00
    Next elapse: Sun 2021-03-21 01:00:00 GMT
       (in UTC): Sun 2021-03-21 01:00:00 UTC
       From now: 59min left
       Iter. #2: Sun 2021-04-04 01:00:00 IST
       (in UTC): Sun 2021-04-04 00:00:00 UTC
       From now: 1 weeks 6 days left           <---- note the 2 week jump here
       Iter. #3: Sun 2021-04-11 01:00:00 IST
       (in UTC): Sun 2021-04-11 00:00:00 UTC
       From now: 2 weeks 6 days left
       Iter. #4: Sun 2021-04-18 01:00:00 IST
       (in UTC): Sun 2021-04-18 00:00:00 UTC
       From now: 3 weeks 6 days left
       Iter. #5: Sun 2021-04-25 01:00:00 IST
       (in UTC): Sun 2021-04-25 00:00:00 UTC
       From now: 1 months 4 days left

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1941335.
---

diff --git a/src/shared/calendarspec.c b/src/shared/calendarspec.c
index 5c666412946..bf24d8d5bbb 100644
--- a/src/shared/calendarspec.c
+++ b/src/shared/calendarspec.c
@@ -1195,15 +1195,18 @@ static int tm_within_bounds(struct tm *tm, bool utc) {
                 return negative_errno();
 
         /* Did any normalization take place? If so, it was out of bounds before */
-        bool good = t.tm_year == tm->tm_year &&
-                    t.tm_mon  == tm->tm_mon  &&
-                    t.tm_mday == tm->tm_mday &&
-                    t.tm_hour == tm->tm_hour &&
-                    t.tm_min  == tm->tm_min  &&
-                    t.tm_sec  == tm->tm_sec;
-        if (!good)
+        int cmp = CMP(t.tm_year, tm->tm_year) ?:
+                  CMP(t.tm_mon, tm->tm_mon) ?:
+                  CMP(t.tm_mday, tm->tm_mday) ?:
+                  CMP(t.tm_hour, tm->tm_hour) ?:
+                  CMP(t.tm_min, tm->tm_min) ?:
+                  CMP(t.tm_sec, tm->tm_sec);
+
+        if (cmp < 0)
+                return -EDEADLK; /* Refuse to go backward */
+        if (cmp > 0)
                 *tm = t;
-        return good;
+        return cmp == 0;
 }
 
 static bool matches_weekday(int weekdays_bits, const struct tm *tm, bool utc) {
diff --git a/src/test/test-calendarspec.c b/src/test/test-calendarspec.c
index c62e6860cf9..4f1d0f64d57 100644
--- a/src/test/test-calendarspec.c
+++ b/src/test/test-calendarspec.c
@@ -214,6 +214,9 @@ int main(int argc, char* argv[]) {
         /* Confirm that timezones in the Spec work regardless of current timezone */
         test_next("2017-09-09 20:42:00 Pacific/Auckland", "", 12345, 1504946520000000);
         test_next("2017-09-09 20:42:00 Pacific/Auckland", "EET", 12345, 1504946520000000);
+        /* Check that we don't start looping if mktime() moves us backwards */
+        test_next("Sun *-*-* 01:00:00 Europe/Dublin", "", 1616412478000000, 1617494400000000);
+        test_next("Sun *-*-* 01:00:00 Europe/Dublin", "IST", 1616412478000000, 1617494400000000);
 
         assert_se(calendar_spec_from_string("test", &c) < 0);
         assert_se(calendar_spec_from_string(" utc", &c) < 0);
diff --git a/test/test-functions b/test/test-functions
index d7f7967e2ff..6b94058fd36 100644
--- a/test/test-functions
+++ b/test/test-functions
@@ -1340,6 +1340,7 @@ install_zoneinfo() {
     inst_any /usr/share/zoneinfo/Asia/Vladivostok
     inst_any /usr/share/zoneinfo/Australia/Sydney
     inst_any /usr/share/zoneinfo/Europe/Berlin
+    inst_any /usr/share/zoneinfo/Europe/Dublin
     inst_any /usr/share/zoneinfo/Europe/Kiev
     inst_any /usr/share/zoneinfo/Pacific/Auckland
     inst_any /usr/share/zoneinfo/Pacific/Honolulu