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From: =?utf-8?q?Zbigniew_J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Sun, 21 Mar 2021 20:59:32 +0100
Subject: shared/calendarspec: abort calculation after 1000 iterations
We have a bug where we seem to enter an infinite loop when running in the
Europe/Dublin timezone. The timezone is "special" because it has negative SAVE
values. The handling of this should obviously be fixed, but let's use a
belt-and-suspenders approach, and gracefully fail if we fail to find an answer
within a specific number of attempts. The code in this function is rather
complex, and it's hard to rule out another bug in the future.
(cherry picked from commit 169615c9a8cdc54d748d4dfc8279be9b3c2bec44)
---
src/shared/calendarspec.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/src/shared/calendarspec.c b/src/shared/calendarspec.c
index 7162592..80acc57 100644
--- a/src/shared/calendarspec.c
+++ b/src/shared/calendarspec.c
@@ -1211,6 +1211,10 @@ static bool matches_weekday(int weekdays_bits, const struct tm *tm, bool utc) {
return (weekdays_bits & (1 << k));
}
+/* A safety valve: if we get stuck in the calculation, return an error.
+ * C.f. https://bugzilla.redhat.com/show_bug.cgi?id=1941335. */
+#define MAX_CALENDAR_ITERATIONS 1000
+
static int find_next(const CalendarSpec *spec, struct tm *tm, usec_t *usec) {
struct tm c;
int tm_usec;
@@ -1224,7 +1228,7 @@ static int find_next(const CalendarSpec *spec, struct tm *tm, usec_t *usec) {
c = *tm;
tm_usec = *usec;
- for (;;) {
+ for (unsigned iteration = 0; iteration < MAX_CALENDAR_ITERATIONS; iteration++) {
/* Normalize the current date */
(void) mktime_or_timegm(&c, spec->utc);
c.tm_isdst = spec->dst;
@@ -1321,6 +1325,14 @@ static int find_next(const CalendarSpec *spec, struct tm *tm, usec_t *usec) {
*usec = tm_usec;
return 0;
}
+
+ /* It seems we entered an infinite loop. Let's gracefully return an error instead of hanging or
+ * aborting. This code is also exercised when timers.target is brought up during early boot, so
+ * aborting here is problematic and hard to diagnose for users. */
+ _cleanup_free_ char *s = NULL;
+ (void) calendar_spec_to_string(spec, &s);
+ return log_warning_errno(SYNTHETIC_ERRNO(EDEADLK),
+ "Infinite loop in calendar calculation: %s", strna(s));
}
static int calendar_spec_next_usec_impl(const CalendarSpec *spec, usec_t usec, usec_t *ret_next) {
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