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Don't add the 2 reserved clusters before we determine if we using fat16/fat32.

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From FreeBSD: https://reviews.freebsd.org/D23082:

Correct off-by-two issue when determining FAT type.

In the code we used NumClusters as the upper (non-inclusive) boundary
of valid cluster number, so the actual value was 2 (CLUST_FIRST) more
than the real number of clusters. This causes a FAT16 media with
65524 clusters be treated as FAT32 and might affect FAT12 media with
4084 clusters as well.

To fix this, we increment NumClusters by CLUST_FIRST after the type
determination.
This commit is contained in:
christos 2020-01-11 16:29:07 +00:00
parent febfde9c6a
commit 08f54aa8c8
1 changed files with 16 additions and 4 deletions
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20
sbin/fsck_msdos/boot.c
View File

@ -27,7 +27,7 @@
#include <sys/cdefs.h>
#ifndef lint
__RCSID("$NetBSD: boot.c,v 1.21 2018/02/08 09:05:17 dholland Exp $");
__RCSID("$NetBSD: boot.c,v 1.22 2020/01/11 16:29:07 christos Exp $");
#endif /* not lint */
#include <stdlib.h>
@ -210,8 +210,12 @@ readboot(int dosfs, struct bootblock *boot)
return FSFATAL;
}
boot->NumClusters = (boot->NumSectors - boot->FirstCluster) / boot->SecPerClust
+ CLUST_FIRST;
/*
* The number of clusters is derived from available data sectors,
* divided by sectors per cluster.
*/
boot->NumClusters =
(boot->NumSectors - boot->FirstCluster) / boot->SecPerClust;
if (boot->flags&FAT32)
boot->ClustMask = CLUST32_MASK;
@ -237,11 +241,19 @@ readboot(int dosfs, struct bootblock *boot)
break;
}
if (boot->NumFatEntries < boot->NumClusters - CLUST_FIRST) {
if (boot->NumFatEntries < boot->NumClusters) {
pfatal("FAT size too small, %u entries won't fit into %u sectors\n",
boot->NumClusters, boot->FATsecs);
return FSFATAL;
}
/*
* There are two reserved clusters. To avoid adding CLUST_FIRST every
* time we perform boundary checks, we increment the NumClusters by 2,
* which is CLUST_FIRST to denote the first out-of-range cluster number.
*/
boot->NumClusters += CLUST_FIRST;
boot->ClusterSize = boot->BytesPerSec * boot->SecPerClust;
boot->NumFiles = 1;