From c5ad70d31acf1c114129102307679acd008900a8 Mon Sep 17 00:00:00 2001
From: Julien Cristau <jcristau@mozilla.com>
Date: Wed, 8 Feb 2023 15:58:24 +0100
Subject: [PATCH] Fix asn1_get_time_t timezone offset

mktime takes an input in local time, but what we have is UTC.  timegm
does the right thing but is a nonstandard GNU and BSD extension, while
Windows has _mkgmtime.
---
 osslsigncode.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/osslsigncode.c b/osslsigncode.c
index e2fcea4..67b7127 100644
--- a/osslsigncode.c
+++ b/osslsigncode.c
@@ -2095,7 +2095,11 @@ static time_t asn1_get_time_t(const ASN1_TIME *s)
 		return INVALID_TIME;
 	}
 	if (ASN1_TIME_to_tm(s, &tm)) {
-		return mktime(&tm);
+#ifdef _WIN32
+		return _mkgmtime(&tm);
+#else
+		return timegm(&tm);
+#endif
 	} else {
 		return INVALID_TIME;
 	}