Module Name: src
Committed By: christos
Date: Sat Jan 11 16:29:07 UTC 2020
Modified Files:
src/sbin/fsck_msdos: boot.c
Log Message:
Don't add the 2 reserved clusters before we determine if we using fat16/fat32.
>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.
To generate a diff of this commit:
cvs rdiff -u -r1.21 -r1.22 src/sbin/fsck_msdos/boot.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sbin/fsck_msdos/boot.c
diff -u src/sbin/fsck_msdos/boot.c:1.21 src/sbin/fsck_msdos/boot.c:1.22
--- src/sbin/fsck_msdos/boot.c:1.21 Thu Feb 8 04:05:17 2018
+++ src/sbin/fsck_msdos/boot.c Sat Jan 11 11:29:07 2020
@@ -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 *bo
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 *bo
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;
