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

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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.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2021-03-22 12:51:47 +01:00
parent 47b0b65766
commit 129cb6e249
3 changed files with 15 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

19
src/shared/calendarspec.c
View file

@ -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) {

3
src/test/test-calendarspec.c
View file

@ -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);

1
test/test-functions
View file

@ -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