kern/93860: [patch] [msdosfs] sectors-per-track limit of MSDOSFS too low

[Oliver Fromme]

>Number:         93860
>Category:       kern
>Synopsis:       [patch] [msdosfs] sectors-per-track limit of MSDOSFS too low
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          change-request
>Submitter-Id:   current-users
>Arrival-Date:   Sun Feb 26 16:10:05 GMT 2006
>Closed-Date:
>Last-Modified:
>Originator:     Oliver Fromme
>Release:        FreeBSD 6-STABLE
>Organization:
secnetix GmbH & Co. KG
		http://www.secnetix.de/bsd
>Environment:

   Problem discovered and patched on RELENG_6.
   Looking at the CVS repository indicates that
   it applies to CURRENT and RELENG_5 as well.

>Description:

   I've recently bought a USB flash memory stick with
   built-in mp3 player.  It's an Elta 8061 OL, the flash
   size is 1 GByte.

   However, mount_msdosfs refused to mount it (EINVAL).
   Reformatting it with newfs_msdos is not an option,
   because the mp3 player only recognizes it when it's
   formatted with its own firmware.

   So I had a closer look at the layout of the file system.
   It's a FAT32 file system with 512 bytes per sector,
   8 sectors per cluster, 63 heads and 224 sectors per track.

   After inspecting the source, I found that the latter
   (224 sectors per track) is the problem.  The source
   says:

        if (!pmp->pm_BytesPerSec || !SecPerClust
                || !pmp->pm_Heads
#ifdef PC98
                || !pmp->pm_SecPerTrack || pmp->pm_SecPerTrack > 255) {
#else
                || !pmp->pm_SecPerTrack || pmp->pm_SecPerTrack > 63) {
#endif
                error = EINVAL;
                goto error_exit;
        }

   I don't have a PC98 machine, so I hit the limit of
   63 sectors per track.  It's completely beyond me why
   there's a different limit for PC98.  Why should my
   USB memory stick work in a PC98 machine, but not in
   an i386 machine?  I simply removed the whole #ifdef
   and kept only the 255 SecPerTrack limit.  Then I could
   mount the memory stick and copy files without any
   problems.

   Please see the patch below.

>How-To-Repeat:

   Try to mount an msdosfs (USB stick, mp3 player) with
   a FAT32 file system that has more than 63 sectors per
   track.

   In case some expert want to have a closer look at the
   file system in question, this is the first MByte of my
   USB stick (/dev/da0), gzipped and uuencoded.  The
   first slice (/dev/da0s1) which contains the msdosfs
   begins at offset 0x4000 (16 KByte).

begin 600 elta.dd.gz
M'XL("!J!^4,"`V5L=&$N9&0`[=S/:YQ%'`?@>9>X&V)C(U6QN3A7#U6C17J+
M6ZP at V*B-`:4@;,FV;!IWZ[OO"I&`6ZR'1`C](SR%7H0>6E:W*T)O*WKK022H
MM)8]6/P12AL:LTVAM>2 at GJ(^#PP,[PQS^`X?WKG,K(UUECI+EY:^_BS,MT?G
M+XSFSU].?OWD:E@<6VVU"Y\.['LZ&_R@\=%JX]V%[YI?CGS_\T8WUWV\>:.9
M/KCX?&.@>;&Y[Y<TM_C(PI7%+/GXE5PKS*_F/R\TLSVO3[:6I\X6N[O2>/+F
MU')C=/6+)'OT\-&9<'0]&\Q/SB0S(PN7SX7]O0<.OW4NR75W+:RE.T]>N)5L
M3-ZQ_D/[?+[W</N;?&]'^UJ^5V at 5PMF'NB-G3G4:O_5NO5Q]KS1;F8XG2FE6
MR2JU:LQ*1V;+X4":UM(X6RM-5ZK'8NU$.2UE_5Y]KIZ5WPD'*_7ZE at .G_X6:
MS20)`^,K5V((867\B?!W32T'````````````````````MH6K(<0[0FYPH_4_
M7@]A)8R'&#9OE7]5V)S;'TM"?JMEXETO%=]X[MG^<FQ[4\N'#I6*ZO#?EJ;%
MTOH=]^]_[\W3^R=?C''O4WOOYO_:1J##"[=G]//?_5/^<_>M_N2WHX/O3[P:
M)XH'#]R;_QMCG=NOBMQ<NO13"&]_>'%WJQ#6SISJ9/G^,QZ]WY_YL?M8=_?P
MT$2MNF?S$8XX7:D?'QYZ+2W7Z[%4G8O'RW,QJ\6T?*16RX:';*7\\X_SG]MB
M_U4'G/^=__^?_W\U````````````````V-ZN;UX+WGEO4Q4`````````````
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`
end

>Fix:

This patch is for RELENG_6, but it should apply as well to
CURRENT and RELENG_5.

--- src/sys/fs/msdosfs/msdosfs_vfsops.c.orig	Tue Oct  4 15:13:57 2005
+++ src/sys/fs/msdosfs/msdosfs_vfsops.c	Sun Feb 26 16:48:00 2006
@@ -479,11 +479,7 @@
 	/* XXX - We should probably check more values here */
 	if (!pmp->pm_BytesPerSec || !SecPerClust
 		|| !pmp->pm_Heads
-#ifdef PC98
     		|| !pmp->pm_SecPerTrack || pmp->pm_SecPerTrack > 255) {
-#else
-		|| !pmp->pm_SecPerTrack || pmp->pm_SecPerTrack > 63) {
-#endif
 		error = EINVAL;
 		goto error_exit;
 	}
>Release-Note:
>Audit-Trail:
>Unformatted: