Correct the calculation of "a leap year" in parseDWM. The calculation

would only match a leap year every 400 years.  The parseDWM code first
showed up in April 2000, so the first time this bug would cause any
confusion is in Feb 2004.

MFC after:	18 days

1 files changed, 43 insertions, 17 deletions

diff --git a/usr.sbin/newsyslog/ptimes.c b/usr.sbin/newsyslog/ptimes.c
index c00b08c..46fe1c7 100644
--- a/usr.sbin/newsyslog/ptimes.c
+++ b/usr.sbin/newsyslog/ptimes.c
@@ -48,6 +48,42 @@ __FBSDID("$FreeBSD$");
 
 #include "extern.h"
 
+static int	 days_pmonth(int month, int year);
+
+/*
+ * Simple routine to calculate the number of days in a given month.
+ */
+static int
+days_pmonth(int month, int year)
+{
+	static const int mtab[] = {31, 28, 31, 30, 31, 30, 31, 31,
+	    30, 31, 30, 31};
+	int ndays;
+
+	ndays = mtab[month];
+
+	if (month == 1) {
+		/*
+		 * We are usually called with a 'tm-year' value
+		 * (ie, the value = the number of years past 1900).
+		 */
+		if (year < 1900)
+			year += 1900;
+		if (year % 4 == 0) {
+			/*
+			 * This is a leap year, as long as it is not a
+			 * multiple of 100, or if it is a multiple of
+			 * both 100 and 400.
+			 */
+			if (year % 100 != 0)
+				ndays++;	/* not multiple of 100 */
+			else if (year % 400 == 0)
+				ndays++;	/* is multiple of 100 and 400 */
+		}
+	}
+	return (ndays);
+}
+
 /*-
  * Parse a limited subset of ISO 8601. The specific format is as follows:
  *
@@ -158,12 +194,11 @@ parse8601(const char *s, time_t *next_time)
 time_t
 parseDWM(char *s, time_t *next_time)
 {
+	int daysmon;
 	char *t;
 	time_t tsecs;
 	struct tm tm, *tmp;
 	long l;
-	int nd;
-	static int mtab[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
 	int WMseen = 0;
 	int Dseen = 0;
 
@@ -172,17 +207,8 @@ parseDWM(char *s, time_t *next_time)
 	if (next_time != NULL)
 		*next_time = (time_t)-1;
 
-	/* set no. of days per month */
-
-	nd = mtab[tm.tm_mon];
-
-	if (tm.tm_mon == 1) {
-		if (((tm.tm_year + 1900) % 4 == 0) &&
-		    ((tm.tm_year + 1900) % 100 != 0) &&
-		    ((tm.tm_year + 1900) % 400 == 0)) {
-			nd++;	/* leap year, 29 days in february */
-		}
-	}
+	/* Save away the number of days in this month */
+	daysmon = days_pmonth(tm.tm_mon, tm.tm_year);
 	tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
 
 	for (;;) {
@@ -218,9 +244,9 @@ parseDWM(char *s, time_t *next_time)
 
 				tm.tm_mday += save;
 
-				if (tm.tm_mday > nd) {
+				if (tm.tm_mday > daysmon) {
 					tm.tm_mon++;
-					tm.tm_mday = tm.tm_mday - nd;
+					tm.tm_mday = tm.tm_mday - daysmon;
 				}
 			}
 			break;
@@ -231,7 +257,7 @@ parseDWM(char *s, time_t *next_time)
 			WMseen++;
 			s++;
 			if (tolower(*s) == 'l') {
-				tm.tm_mday = nd;
+				tm.tm_mday = daysmon;
 				s++;
 				t = s;
 			} else {
@@ -239,7 +265,7 @@ parseDWM(char *s, time_t *next_time)
 				if (l < 1 || l > 31)
 					return (-1);
 
-				if (l > nd)
+				if (l > daysmon)
 					return (-1);
 				tm.tm_mday = l;
 			}