Bug in date converting functions DOS<=>UNIX in FAT, NCPFS and SMBFS drivers

From: "Igor Yu. Zhbanov" <bsg@uniyar.ac.ru>
To: linux-kernel@vger.kernel.org, vandrove@vc.cvut.cz, vl@kki.org,
	linware@sh.cvut.cz, urban@svenskatest.se, samba@samba.org,
	chaffee@cs.berkeley.edu
Subject: Bug in date converting functions DOS<=>UNIX in FAT, NCPFS and SMBFS drivers
Date: Fri, 24 Nov 2000 16:30:05 +0300 (MSK)	[thread overview]
Message-ID: <Pine.GSO.3.96.SK.1001124162224.25896A-200000@univ.uniyar.ac.ru> (raw)

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1173 bytes --]

Hello!

I have found a bug in drivers of file systems which use a DOS-like format
of date (16 bit: years since 1980 - 7 bits, month - 4 bits, day - 5 bits).

There are two problems:
1) It is unable to convert UNIX-like dates before 1980 to DOS-like date format.
2) VFAT for example have three kinds of dates: creation date, modification date
   and access date. Sometimes one of these dates is set to zero (which indicates
   that this date is not set). Zero is not a valid date (e.g. months are
   numbered from one, not from zero) and can't be properly converted to
   UNIX-like format of date (it was converted to date before 1980).

I have found FAT, NCPFS and SMBFS drivers subject to this problems. Patch for
fixing these bugs attached.

Also I have a question about VFAT file system. VFAT have not access time fields
in directory entries but it has access date fields. Currently information about
the time of last access is not supported for VFAT file system in LINUX. Is this
correct? Maybe access time should be truncated to days.

Thank you.

P.S. Since I'm not currently subscribed to Linux Kernel Mailing List please CC:
all replies to bsg@uniyar.ac.ru if any.

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diff -ur linux-2.2.17/fs/fat/misc.c linux/fs/fat/misc.c

--- linux-2.2.17/fs/fat/misc.c	Thu May  4 04:16:46 2000
+++ linux/fs/fat/misc.c	Wed Nov 22 14:05:08 2000
@@ -2,6 +2,8 @@
  *  linux/fs/fat/misc.c
  *
  *  Written 1992,1993 by Werner Almesberger
+ *  22/11/2000 - Fixed fat_date_unix2dos for dates earlier than 01/01/1980
+ *		 and date_dos2unix for date==0 by Igor Zhbanov(bsg@uniyar.ac.ru)
  */
 
 #include <linux/fs.h>
@@ -288,7 +290,9 @@
 {
 	int month,year,secs;
 
-	month = ((date >> 5) & 15)-1;
+	/* first subtract and mask after that... Otherwise, if
+	   date == 0, bad things happen */
+	month = ((date >> 5) - 1) & 15;
 	year = date >> 9;
 	secs = (time & 31)*2+60*((time >> 5) & 63)+(time >> 11)*3600+86400*
 	    ((date & 31)-1+day_n[month]+(year/4)+year*365-((year & 3) == 0 &&
@@ -310,6 +314,8 @@
 	unix_date -= sys_tz.tz_minuteswest*60;
 	if (sys_tz.tz_dsttime) unix_date += 3600;
 
+	if (unix_date < 315532800)
+		unix_date = 315532800; /* Jan 1 GMT 00:00:00 1980. But what about another time zone? */
 	*time = (unix_date % 60)/2+(((unix_date/60) % 60) << 5)+
 	    (((unix_date/3600) % 24) << 11);
 	day = unix_date/86400-3652;
diff -ur linux-2.2.17/fs/ncpfs/dir.c linux/fs/ncpfs/dir.c
--- linux-2.2.17/fs/ncpfs/dir.c	Thu Jun  8 01:26:43 2000
+++ linux/fs/ncpfs/dir.c	Wed Nov 22 14:06:09 2000
@@ -5,6 +5,8 @@
  *  Modified for big endian by J.F. Chadima and David S. Miller
  *  Modified 1997 Peter Waltenberg, Bill Hawes, David Woodhouse for 2.1 dcache
  *  Modified 1998 Wolfram Pienkoss for NLS
+ *  22/11/2000 - Fixed ncp_date_unix2dos for dates earlier than 01/01/1980
+ *		 by Igor Zhbanov(bsg@uniyar.ac.ru)
  *
  */
 
@@ -1158,6 +1160,8 @@
 	int day, year, nl_day, month;
 
 	unix_date = utc2local(unix_date);
+	if (unix_date < 315532800)
+		unix_date = 315532800; /* Jan 1 GMT 00:00:00 1980. But what about another time zone? */
 	*time = (unix_date % 60) / 2 + (((unix_date / 60) % 60) << 5) +
 	    (((unix_date / 3600) % 24) << 11);
 	day = unix_date / 86400 - 3652;
diff -ur linux-2.2.17/fs/smbfs/ChangeLog linux/fs/smbfs/ChangeLog
--- linux-2.2.17/fs/smbfs/ChangeLog	Mon Sep  4 21:39:27 2000
+++ linux/fs/smbfs/ChangeLog	Wed Nov 22 14:10:40 2000
@@ -1,5 +1,10 @@
 ChangeLog for smbfs.
 
+2000-11-22 Igor Zhbanov <bsg@uniyar.ac.ru>
+
+	* proc.c: fixed date_unix2dos for dates earlier than 01/01/1980
+	  and date_dos2unix for date==0
+
 2000-07-20 Urban Widmark <urban@svenskatest.se>
 
 	* proc.c: fix 2 places where bad server responses could cause an Oops.
diff -ur linux-2.2.17/fs/smbfs/proc.c linux/fs/smbfs/proc.c
--- linux-2.2.17/fs/smbfs/proc.c	Mon Sep  4 21:39:27 2000
+++ linux/fs/smbfs/proc.c	Wed Nov 22 14:13:32 2000
@@ -169,7 +169,9 @@
 	int month, year;
 	time_t secs;
 
-	month = ((date >> 5) & 15) - 1;
+	/* first subtract and mask after that... Otherwise, if
+	   date == 0, bad things happen */
+	month = ((date >> 5) - 1) & 15;
 	year = date >> 9;
 	secs = (time & 31) * 2 + 60 * ((time >> 5) & 63) + (time >> 11) * 3600 + 86400 *
 	    ((date & 31) - 1 + day_n[month] + (year / 4) + year * 365 - ((year & 3) == 0 &&
@@ -188,6 +190,8 @@
 	int day, year, nl_day, month;
 
 	unix_date = utc2local(server, unix_date);
+	if (unix_date < 315532800)
+		unix_date = 315532800; /* Jan 1 GMT 00:00:00 1980. But what about another time zone? */
 	*time = (unix_date % 60) / 2 +
 		(((unix_date / 60) % 60) << 5) +
 		(((unix_date / 3600) % 24) << 11);
