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In VOLUME_ReadFATSuperblock:

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- do not test on the JMP instruction: most boot blocks have that
- test instead on the "FAT" strings first, before the size
  calculation
- do some parameter checking to prevent arithmetic errors
- use meaningful names instead of block offsets
(based on a rejected patch from Vincent Béron).
This commit is contained in:
Rein Klazes 2004-10-28 21:00:36 +00:00 committed by Alexandre Julliard
parent e50a27de04
commit 073329fa1b
1 changed files with 38 additions and 17 deletions
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55
dlls/kernel/volume.c
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@ -491,29 +491,50 @@ static enum fs_type VOLUME_ReadFATSuperblock( HANDLE handle, BYTE *buff )
size != SUPERBLOCK_SIZE)
return FS_ERROR;
if (buff[0] == 0xE9 || (buff[0] == 0xEB && buff[2] == 0x90))
/* FIXME: do really all FAT have their name beginning with
* "FAT" ? (At least FAT12, FAT16 and FAT32 have :)
*/
if (!memcmp(buff+0x36, "FAT", 3) || !memcmp(buff+0x52, "FAT", 3))
{
/* guess which type of FAT we have */
unsigned int sz, nsect, nclust;
sz = GETWORD(buff, 0x16);
if (!sz) sz = GETLONG(buff, 0x24);
nsect = GETWORD(buff, 0x13);
if (!nsect) nsect = GETLONG(buff, 0x20);
nsect -= GETWORD(buff, 0x0e) + buff[0x10] * sz +
(GETWORD(buff, 0x11) * 32 + (GETWORD(buff, 0x0b) - 1)) / GETWORD(buff, 0x0b);
nclust = nsect / buff[0x0d];
int reasonable;
unsigned int sectors,
sect_per_fat,
total_sectors,
num_boot_sectors,
num_fats,
num_root_dir_ents,
bytes_per_sector,
sectors_per_cluster,
nclust;
sect_per_fat = GETWORD(buff, 0x16);
if (!sect_per_fat) sect_per_fat = GETLONG(buff, 0x24);
total_sectors = GETWORD(buff, 0x13);
if (!total_sectors)
total_sectors = GETLONG(buff, 0x20);
num_boot_sectors = GETWORD(buff, 0x0e);
num_fats = buff[0x10];
num_root_dir_ents = GETWORD(buff, 0x11);
bytes_per_sector = GETWORD(buff, 0x0b);
sectors_per_cluster = buff[0x0d];
/* check if the parameters are reasonable and will not cause
* arithmetic errors in the calculation */
reasonable = num_boot_sectors < 16 &&
num_fats < 16 &&
bytes_per_sector >= 512 && bytes_per_sector % 512 == 0 &&
sectors_per_cluster > 1;
if (!reasonable) return FS_UNKNOWN;
sectors = total_sectors - num_boot_sectors - num_fats * sect_per_fat -
(num_root_dir_ents * 32 + bytes_per_sector - 1) / bytes_per_sector;
nclust = sectors / sectors_per_cluster;
if ((buff[0x42] == 0x28 || buff[0x42] == 0x29) &&
!memcmp(buff+0x52, "FAT", 3)) return FS_FAT32;
if (nclust < 65525)
{
if (buff[0x26] == 0x29 && !memcmp(buff+0x36, "FAT", 3))
{
/* FIXME: do really all FAT have their name beginning with
* "FAT" ? (At least FAT12, FAT16 and FAT32 have :)
*/
if ((buff[0x26] == 0x28 || buff[0x26] == 0x29) &&
!memcmp(buff+0x36, "FAT", 3))
return FS_FAT1216;
}
}
else if (!memcmp(buff+0x52, "FAT", 3)) return FS_FAT32;
}
return FS_UNKNOWN;
}