*** This bug is a security vulnerability ***

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UTC ticks SI seconds in step with TAI (International Atomic Time), but
in order to keep in sync with UT1 which is defined by the earth's
rotation, UTC is occasionally adjusted. In other words, in order to keep
UTC 00:00:00 within a second of midnight at the Prime Meridian, leap
seconds are added.

See: https://en.wikipedia.org/wiki/Leap_second

So I tested it.

I booted a live copy of Natty and went for a historic leap second:

date --rfc-3339=seconds -s '2008-12-31 23:59:54+00:00'; hwclock -w
while true; do date --rfc-3339=ns; sleep 0.25; done >> /mnt/time.log

time.log:
2008-12-31 23:59:57.753497430+00:00
2008-12-31 23:59:58.006601830+00:00
2008-12-31 23:59:58.259626718+00:00
2008-12-31 23:59:58.512632697+00:00
2008-12-31 23:59:58.765677765+00:00
2008-12-31 23:59:59.018668172+00:00
2008-12-31 23:59:59.271679983+00:00
2008-12-31 23:59:59.524653233+00:00
2008-12-31 23:59:59.777697760+00:00
2009-01-01 00:00:00.030698916+00:00 <-- Where is the leap second?
2009-01-01 00:00:00.283682058+00:00
2009-01-01 00:00:00.536682453+00:00
2009-01-01 00:00:00.789704596+00:00
2009-01-01 00:00:01.042716625+00:00
2009-01-01 00:00:01.295720967+00:00
2009-01-01 00:00:01.548714966+00:00
2009-01-01 00:00:01.801750574+00:00
2009-01-01 00:00:02.054801900+00:00
2009-01-01 00:00:02.307836286+00:00
2009-01-01 00:00:02.560842969+00:00
2009-01-01 00:00:02.813878513+00:00
2009-01-01 00:00:03.066923251+00:00
2009-01-01 00:00:03.319920865+00:00

So either there should be a 23:59:60 leap second, or the system timezone
should not be called UTC, but the more ambiguous term 'Universal Time'.

I also tried 1998 and 2005. A leap second has been announced for this
June 30.

I think that issues with time can potentially cause or trigger serious
bugs elsewhere. So I'm marking this as a security vulnerability just-in-
case.

** Affects: gnome-control-center (Ubuntu)
     Importance: Undecided
         Status: New

-- 
UTC is incorrectly implemented; it does not handle leap seconds
https://bugs.launchpad.net/bugs/970966
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