libinstaller/fat.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 1998-2008 H. Peter Anvin - All Rights Reserved
   4  *   Copyright 2009-2010 Intel Corporation; author H. Peter Anvin
   5  *
   6  *   This program is free software; you can redistribute it and/or modify
   7  *   it under the terms of the GNU General Public License as published by
   8  *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
   9  *   Boston MA 02111-1307, USA; either version 2 of the License, or
  10  *   (at your option) any later version; incorporated herein by reference.
  11  *
  12  * ----------------------------------------------------------------------- */
  13
  14 /*
  15  * fat.c - Initial sanity check for FAT-based installers
  16  */
  17
  18 #define _XOPEN_SOURCE 500       /* Required on glibc 2.x */
  19 #define _BSD_SOURCE
  20 #include <stdio.h>
  21 #include <inttypes.h>
  22 #include <string.h>
  23 #include <stddef.h>
  24 #include <stdlib.h>
  25
  26 #include "syslinux.h"
  27 #include "syslxint.h"
  28
  29 void syslinux_make_bootsect(void *bs)
  30 {
  31     struct boot_sector *bootsect = bs;
  32     const struct boot_sector *sbs =
  33         (const struct boot_sector *)boot_sector;
  34
  35     memcpy(&bootsect->bsHead, &sbs->bsHead, bsHeadLen);
  36     memcpy(&bootsect->bsCode, &sbs->bsCode, bsCodeLen);
  37 }
  38
  39 /*
  40  * Check to see that what we got was indeed an MS-DOS boot sector/superblock;
  41  * Return NULL if OK and otherwise an error message;
  42  */
  43 const char *syslinux_check_bootsect(const void *bs)
  44 {
  45     int sectorsize;
  46     long long sectors, fatsectors, dsectors;
  47     long long clusters;
  48     int rootdirents, clustersize;
  49     const struct boot_sector *sectbuf = bs;
  50
  51     /* Must be 0xF0 or 0xF8..0xFF */
  52     if (get_8(&sectbuf->bsMedia) != 0xF0 && get_8(&sectbuf->bsMedia) < 0xF8)
  53         return "invalid media signature (not a FAT filesystem?)";
  54
  55     sectorsize = get_16(&sectbuf->bsBytesPerSec);
  56     if (sectorsize == SECTOR_SIZE)
  57         ;                       /* ok */
  58     else if (sectorsize >= 512 && sectorsize <= 4096 &&
  59              (sectorsize & (sectorsize - 1)) == 0)
  60         return "unsupported sectors size";
  61     else
  62         return "impossible sector size";
  63
  64     clustersize = get_8(&sectbuf->bsSecPerClust);
  65     if (clustersize == 0 || (clustersize & (clustersize - 1)))
  66         return "impossible cluster size";
  67
  68     sectors = get_16(&sectbuf->bsSectors);
  69     sectors = sectors ? sectors : get_32(&sectbuf->bsHugeSectors);
  70
  71     dsectors = sectors - get_16(&sectbuf->bsResSectors);
  72
  73     fatsectors = get_16(&sectbuf->bsFATsecs);
  74     fatsectors = fatsectors ? fatsectors : get_32(&sectbuf->bs32.FATSz32);
  75     fatsectors *= get_8(&sectbuf->bsFATs);
  76     dsectors -= fatsectors;
  77
  78     rootdirents = get_16(&sectbuf->bsRootDirEnts);
  79     dsectors -= (rootdirents + sectorsize / 32 - 1) / sectorsize;
  80
  81     if (dsectors < 0)
  82         return "negative number of data sectors";
  83
  84     if (fatsectors == 0)
  85         return "zero FAT sectors";
  86
  87     clusters = dsectors / clustersize;
  88
  89     if (clusters < 0xFFF5) {
  90         /* FAT12 or FAT16 */
  91
  92         if (!get_16(&sectbuf->bsFATsecs))
  93             return "zero FAT sectors (FAT12/16)";
  94
  95         if (get_8(&sectbuf->bs16.BootSignature) == 0x29) {
  96             if (!memcmp(&sectbuf->bs16.FileSysType, "FAT12   ", 8)) {
  97                 if (clusters >= 0xFF5)
  98                     return "more than 4084 clusters but claims FAT12";
  99             } else if (!memcmp(&sectbuf->bs16.FileSysType, "FAT16   ", 8)) {
 100                 if (clusters < 0xFF5)
 101                     return "less than 4084 clusters but claims FAT16";
 102             } else if (!memcmp(&sectbuf->bs16.FileSysType, "FAT32   ", 8)) {
 103                     return "less than 65525 clusters but claims FAT32";
 104             } else if (memcmp(&sectbuf->bs16.FileSysType, "FAT     ", 8)) {
 105                 static char fserr[] =
 106                     "filesystem type \"????????\" not supported";
 107                 memcpy(fserr + 17, &sectbuf->bs16.FileSysType, 8);
 108                 return fserr;
 109             }
 110         }
 111     } else if (clusters < 0x0FFFFFF5) {
 112         /*
 113          * FAT32...
 114          *
 115          * Moving the FileSysType and BootSignature was a lovely stroke
 116          * of M$ idiocy...
 117          */
 118         if (get_8(&sectbuf->bs32.BootSignature) != 0x29 ||
 119             memcmp(&sectbuf->bs32.FileSysType, "FAT32   ", 8))
 120             return "missing FAT32 signature";
 121     } else {
 122         return "impossibly large number of clusters";
 123     }
 124
 125     return NULL;
 126 }