This function uses signed integers for the unix_date and local variables -

if a negative number is supplied and the leap-year condition is not met,
month will be 0, leading to a later read of day_n[-1]
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Cc: Petr Vandrovec <VANDROVE@vc.cvut.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/ncpfs/dir.c

@@ -1241,7 +1241,7 @@ ncp_date_unix2dos(int unix_date, __le16 *time, __le16 *date)
 		month = 2;
 	} else {
 		nl_day = (year & 3) || day <= 59 ? day : day - 1;
-		for (month = 0; month < 12; month++)
+		for (month = 1; month < 12; month++)
 			if (day_n[month] > nl_day)
 				break;
 	}