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lib/50380: strptime() returns incorrect values in tm_gmtoff
>Synopsis: strptime() returns incorrect values in tm_gmtoff
>Arrival-Date: Thu Oct 29 14:05:01 +0000 2015
>Originator: Balazs Scheidler
>Release: /* $NetBSD: strptime.c,v 1.49 2015/10/09 17:21:45 christos Exp $ */
I was trying to reuse the strptime() implementation from NetBSD in a project of mine, specifically it had good support for %z and %Z specifiers.
The issue is that it doesn't work, and I've fixed that up in my local tree, but I've figured those should be fixed upstream as well.
tm_gmtoff should be in seconds, at least tm(3) documents it as such:
$ grep -n TM_GMTOFF strptime.orig.c
429: tm->TM_GMTOFF = 0;
442: tm->TM_GMTOFF = -(timezone);
485: tm->TM_GMTOFF = 0;
502: tm->TM_GMTOFF = -5 - i;
514: tm->TM_GMTOFF = -4 - i;
528: tm->TM_GMTOFF =
529: ('A' - 1) - (int)*bp;
531: tm->TM_GMTOFF = 'A' - (int)*bp;
533: tm->TM_GMTOFF = (int)*bp - 'M';
574: tm->TM_GMTOFF = offs;
Of course zero initialization doesn't matter, but a few of the instances above are definitely bogus:
* strptime.c:443: "timezone" seems to be a function on NetBSD (unlike Linux, where it is actually the seconds from UTC as set in localtime)
* strptime.c:502, 514, 529, 531 & 533: expressions such as "(-5 - i)" and "-4 - i" seems to set gmtoff as hours and not seconds
* strptime.c:574: is the code that parses %z, there "offs" must be multiplied by 3600/100=36 to get the correct value.
I am not personally using NetBSD, but the software I write does support NetBSD, and the exact reason I am planning a private
strptime() implementation is its unreliability on various platforms, especially wrt timezones.
All in all, I am personally not affected by the bug right now, but some of my users are or could be in the future.
I've figured I'd file this PR to make NetBSD better.
Well, just write a simple program that calls strptime() with %z and/or %Z format strings and watch tm_gmtoff being set to an incorrect value.
The timezone() function part I don't really know, but the others are either to be multiplied by 3600 (to get seconds from hours), the "%z" one at the end should be multiplied by 36 to get the proper value.
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