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/* ----------------------------------------------------------------------- *
*
* Copyright 1998-2008 H. Peter Anvin - All Rights Reserved
* Copyright 2009-2010 Intel Corporation; author H. Peter Anvin
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, Inc., 53 Temple Place Ste 330,
* Boston MA 02111-1307, USA; either version 2 of the License, or
* (at your option) any later version; incorporated herein by reference.
*
* ----------------------------------------------------------------------- */
/*
* fat.c - Initial sanity check for FAT-based installers
*/
#define _XOPEN_SOURCE 500 /* Required on glibc 2.x */
#define _BSD_SOURCE
#include <stdio.h>
#include <inttypes.h>
#include <string.h>
#include <stddef.h>
#include <stdlib.h>
#include "syslinux.h"
#include "syslxint.h"
void syslinux_make_bootsect(void *bs)
{
struct boot_sector *bootsect = bs;
const struct boot_sector *sbs =
(const struct boot_sector *)boot_sector;
memcpy(&bootsect->bsHead, &sbs->bsHead, bsHeadLen);
memcpy(&bootsect->bsCode, &sbs->bsCode, bsCodeLen);
}
/*
* Check to see that what we got was indeed an MS-DOS boot sector/superblock;
* Return NULL if OK and otherwise an error message;
*/
const char *syslinux_check_bootsect(const void *bs)
{
int sectorsize;
long long sectors, fatsectors, dsectors;
long long clusters;
int rootdirents, clustersize;
const struct boot_sector *sectbuf = bs;
/* Must be 0xF0 or 0xF8..0xFF */
if (get_8(§buf->bsMedia) != 0xF0 && get_8(§buf->bsMedia) < 0xF8)
return "invalid media signature (not a FAT filesystem?)";
sectorsize = get_16(§buf->bsBytesPerSec);
if (sectorsize == SECTOR_SIZE)
; /* ok */
else if (sectorsize >= 512 && sectorsize <= 4096 &&
(sectorsize & (sectorsize - 1)) == 0)
return "unsupported sectors size";
else
return "impossible sector size";
clustersize = get_8(§buf->bsSecPerClust);
if (clustersize == 0 || (clustersize & (clustersize - 1)))
return "impossible cluster size";
sectors = get_16(§buf->bsSectors);
sectors = sectors ? sectors : get_32(§buf->bsHugeSectors);
dsectors = sectors - get_16(§buf->bsResSectors);
fatsectors = get_16(§buf->bsFATsecs);
fatsectors = fatsectors ? fatsectors : get_32(§buf->bs32.FATSz32);
fatsectors *= get_8(§buf->bsFATs);
dsectors -= fatsectors;
rootdirents = get_16(§buf->bsRootDirEnts);
dsectors -= (rootdirents + sectorsize / 32 - 1) / sectorsize;
if (dsectors < 0)
return "negative number of data sectors";
if (fatsectors == 0)
return "zero FAT sectors";
clusters = dsectors / clustersize;
if (clusters < 0xFFF5) {
/* FAT12 or FAT16 */
if (!get_16(§buf->bsFATsecs))
return "zero FAT sectors (FAT12/16)";
if (get_8(§buf->bs16.BootSignature) == 0x29) {
if (!memcmp(§buf->bs16.FileSysType, "FAT12 ", 8)) {
if (clusters >= 0xFF5)
return "more than 4084 clusters but claims FAT12";
} else if (!memcmp(§buf->bs16.FileSysType, "FAT16 ", 8)) {
if (clusters < 0xFF5)
return "less than 4084 clusters but claims FAT16";
} else if (!memcmp(§buf->bs16.FileSysType, "FAT32 ", 8)) {
return "less than 65525 clusters but claims FAT32";
} else if (memcmp(§buf->bs16.FileSysType, "FAT ", 8)) {
static char fserr[] =
"filesystem type \"????????\" not supported";
memcpy(fserr + 17, §buf->bs16.FileSysType, 8);
return fserr;
}
}
} else if (clusters < 0x0FFFFFF5) {
/*
* FAT32...
*
* Moving the FileSysType and BootSignature was a lovely stroke
* of M$ idiocy...
*/
if (get_8(§buf->bs32.BootSignature) != 0x29 ||
memcmp(§buf->bs32.FileSysType, "FAT32 ", 8))
return "missing FAT32 signature";
} else {
return "impossibly large number of clusters";
}
return NULL;
}
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