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Index: sbin/fsck_msdosfs/boot.c
===================================================================
--- sbin/fsck_msdosfs/boot.c
+++ sbin/fsck_msdosfs/boot.c
@@ -28,7 +28,7 @@
#include <sys/cdefs.h>
#ifndef lint
-__RCSID("$NetBSD: boot.c,v 1.11 2006/06/05 16:51:18 christos Exp ");
+__RCSID("$NetBSD: boot.c,v 1.21 2018/02/08 09:05:17 dholland Exp $");
static const char rcsid[] =
"$FreeBSD$";
#endif /* not lint */
@@ -250,7 +250,7 @@
boot->FATsecs = boot->bpbFATsmall;
}
- if (boot->FATsecs > UINT32_MAX / boot->bpbFATs) {
+ if (boot->FATsecs < 1 || boot->FATsecs > UINT32_MAX / boot->bpbFATs) {
pfatal("Invalid FATs(%u) with FATsecs(%zu)",
boot->bpbFATs, (size_t)boot->FATsecs);
return FSFATAL;
@@ -266,8 +266,11 @@
return FSFATAL;
}
- boot->NumClusters = (boot->NumSectors - boot->FirstCluster) / boot->bpbSecPerClust +
- CLUST_FIRST;
+ /*
+ * The number of clusters is derived from available data sectors, divided
+ * by sectors per cluster.
+ */
+ boot->NumClusters = (boot->NumSectors - boot->FirstCluster) / boot->bpbSecPerClust;
if (boot->flags & FAT32) {
if (boot->NumClusters > (CLUST_RSRVD & CLUST32_MASK)) {
@@ -310,11 +313,19 @@
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
+ * when 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->bpbBytesPerSec * boot->bpbSecPerClust;
boot->NumFiles = 1;
@@ -356,7 +367,7 @@
* support for FAT32) doesn't maintain the FSINFO block
* correctly, it has to be fixed pretty often.
*
- * Therefor, we handle the FSINFO block only informally,
+ * Therefore, we handle the FSINFO block only informally,
* fixing it if necessary, but otherwise ignoring the
* fact that it was incorrect.
*/

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