[tz] zdump bug?

Arthur David Olson arthurdavidolson at gmail.com
Sun Oct 28 23:21:18 UTC 2018

If this is a bug I'd characterize it as a localtime.c bug rather than a
zdump bug.

Note first that zdump arguments are time zone names rather than file names.
However, the localtime.c code is prepared to use a zone name as the name of
a file when appropriate. If a zdump argument beginning with a slash is
passed to tzalloc, it will be taken as an absolute filename. But if a name
does NOT begin with a slash (for example, "./New_York") it is taken as a
name within the default time zone directory. In the case at hand, there's
no "New_York" file in the default directory (although there is an
"America/New_York" file), so the software punts to its default; thus the
differing behaviors. The "taken as a name within the default time zone
directory" behavior is arguably worng (and, even if not worng, might best
be documented).

The relevant code is in the "tzloadbody" function. There's some complexity
in that code that may not be necessary. Since time zone code gets compiled
into programs run with root privileges, we want to ensure that the real
user is entitled to read a file specified as the source of time zone
information; that's done with an "access" call. The code tries to avoid the
access call in "safe" cases--cases where the file is sure to be somewhere
under zoneinfo (not specified as an absolute file name, and with no
possibility of a ".." in the name). If we're willing to call access in all
cases, the code for avoiding the access call can go.


On Sun, Oct 28, 2018 at 6:31 PM Matt Johnson <mj1856 at hotmail.com> wrote:

> I notice when I run zdump like this:
> zdump /usr/share/zoneinfo/America/New_York
> The output is normal:
> America/New_York  Sun Oct 28 18:23:35 2018 EDT
> But if I change to the America directory...
> cd /usr/share/zoneinfo/America
> zdump ./New_York
> The output is missing the abbreviation:
> ./New_York  Sun Oct 28 22:23:48 2018
> Is this expected? Seems like a subtle bug to me.  The abbreviations are
> also missing with -v output.
> (Ran on Ubuntu Linux 16.04.5 LTS)
> Thanks,
> Matt
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