bin/153426: [patch] fsck_msdosfs only works with sector size 512

[Keith White]

>Number:         153426
>Category:       bin
>Synopsis:       [patch] fsck_msdosfs only works with sector size 512
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          update
>Submitter-Id:   current-users
>Arrival-Date:   Fri Dec 24 13:10:11 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator:     Keith White
>Release:        FreeBSD 9.0-CURRENT i386
>Organization:
>Environment:
System: FreeBSD demo 9.0-CURRENT FreeBSD 9.0-CURRENT #49: Mon Nov 22 07:00:30 EST 2010 kwhite at demo:/usr/src/obj/usr/src/sys/U100 i386


>Description:

It is possible to create and use an msdos filesystem with 2048-byte
sectors; but it is not possible to "fsck" it.  "fsck_msdosfs" on
such a fileystem returns:
          "could not read boot block (Invalid argument)"

>How-To-Repeat:

         dd if=/dev/zero bs=1m of=msdos.img count=20
         MD=`mdconfig -af msdos.img`
         gnop create -S 2048 -v $MD
         newfs_msdos -n1 $MD.nop
         fsck_msdosfs /dev/$MD.nop
         ** /dev/md4.nop
         could not read boot block (Invalid argument)
         ...
         mount -t msdosfs /dev/$MD.nop /mnt

>Fix:

The following POC patch uses DIOCGSECTORSIZE instead of a fixed value of DOSBOOTBLOCKSIZE.

=============
--- src/sbin/fsck_msdosfs/boot.c.orig   2010-07-03 06:49:57.000000000 -0400
+++ src/sbin/fsck_msdosfs/boot.c        2010-12-24 05:49:09.000000000 -0500
@@ -35,6 +35,7 @@
  #include <string.h>
  #include <stdio.h>
  #include <unistd.h>
+#include <sys/disk.h>

  #include "ext.h"
  #include "fsutil.h"
@@ -47,11 +48,23 @@
         u_char backup[DOSBOOTBLOCKSIZE];
         int ret = FSOK;
         int i;
+       u_char *tblock;
+       unsigned int sectorsize;

-       if (read(dosfs, block, sizeof block) != sizeof block) {
+       if ((ioctl(dosfs, DIOCGSECTORSIZE, &sectorsize) == -1) || sectorsize < sizeof block) {
+               printf("** could not get valid device sectorsize, assuming %d\n", sizeof block);
+               sectorsize = sizeof block;
+       }
+       tblock = (u_char *)malloc(sectorsize);
+       if (read(dosfs, tblock, sectorsize) != sectorsize) {
                 perror("could not read boot block");
                 return FSFATAL;
         }
+       memcpy(block, tblock, sizeof block);
+       free(tblock);
+       if (sectorsize != sizeof block) {
+               printf("** non-standard sectorsize of %d\n", sectorsize);
+       }

         if (block[510] != 0x55 || block[511] != 0xaa) {
                 pfatal("Invalid signature in boot block: %02x%02x",
=============

>Release-Note:
>Audit-Trail:
>Unformatted:
 To: FreeBSD-gnats-submit at freebsd.org
 Subject: [patch] fsck_msdosfs only works with sector size 512
 From: Keith White <kwhite at uottawa.ca>
 Reply-To: Keith White <kwhite at uottawa.ca>
 Cc: kwhite at uottawa.ca
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