From a6e075a2c40be1745f1ae0b9ba210ce06438179d Mon Sep 17 00:00:00 2001
From: yuripv <yuripv@FreeBSD.org>
Date: Wed, 17 Oct 2018 14:51:43 +0000
Subject: [PATCH] strptime: fix parsing of tm_year when both %C and %y appear
 in the format string in arbitrary order.  This makes the related test cases
 in lib/libc/tests/time (not yet connected to the build) pass.

While here, don't error on negative tm_year value based on the
APPLICATION USAGE in
http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/time.h.html
(glibc does the same):

tm_year is a signed value; therefore, years before 1900 may be represented.

Approved by:	re (gjb), kib (mentor)
Differential Revision:	https://reviews.freebsd.org/D17550
---
 lib/libc/stdtime/strptime.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/lib/libc/stdtime/strptime.c b/lib/libc/stdtime/strptime.c
index 78cef6bf839e..e011a7fe8dc8 100644
--- a/lib/libc/stdtime/strptime.c
+++ b/lib/libc/stdtime/strptime.c
@@ -95,6 +95,7 @@ _strptime(const char *buf, const char *fmt, struct tm *tm, int *GMTp,
 	int	i, len;
 	int flags;
 	int Ealternative, Oalternative;
+	int century, year;
 	const struct lc_time_T *tptr = __get_current_time_locale(locale);
 	static int start_of_month[2][13] = {
 		{0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365},
@@ -102,6 +103,8 @@ _strptime(const char *buf, const char *fmt, struct tm *tm, int *GMTp,
 	};
 
 	flags = FLAG_NONE;
+	century = -1;
+	year = -1;
 
 	ptr = fmt;
 	while (*ptr != 0) {
@@ -146,10 +149,8 @@ _strptime(const char *buf, const char *fmt, struct tm *tm, int *GMTp,
 				i += *buf - '0';
 				len--;
 			}
-			if (i < 19)
-				return (NULL);
 
-			tm->tm_year = i * 100 - TM_YEAR_BASE;
+			century = i;
 			flags |= FLAG_YEAR;
 
 			break;
@@ -527,13 +528,9 @@ _strptime(const char *buf, const char *fmt, struct tm *tm, int *GMTp,
 				len--;
 			}
 			if (c == 'Y')
-				i -= TM_YEAR_BASE;
-			if (c == 'y' && i < 69)
-				i += 100;
-			if (i < 0)
-				return (NULL);
+				century = i / 100;
+			year = i % 100;
 
-			tm->tm_year = i;
 			flags |= FLAG_YEAR;
 
 			break;
@@ -611,6 +608,17 @@ _strptime(const char *buf, const char *fmt, struct tm *tm, int *GMTp,
 		}
 	}
 
+	if (century != -1 || year != -1) {
+		if (year == -1)
+			year = 0;
+		if (century == -1) {
+			if (year < 69)
+				year += 100;
+		} else
+			year += century * 100 - TM_YEAR_BASE;
+		tm->tm_year = year;
+	}
+
 	if (!(flags & FLAG_YDAY) && (flags & FLAG_YEAR)) {
 		if ((flags & (FLAG_MONTH | FLAG_MDAY)) ==
 		    (FLAG_MONTH | FLAG_MDAY)) {