svn commit: r357196 - stable/12/sbin/fsck_msdosfs

[Xin LI]

Author: delphij
Date: Tue Jan 28 07:49:52 2020
New Revision: 357196
URL: https://svnweb.freebsd.org/changeset/base/357196

Log:
  MFC r356629, r356636
  
  r356629:
  Apply typo fix from NetBSD, we have already applied all NetBSD changes so
  update the NetBSD tag while I'm there.
  
  r356636:
  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.
  
  PR:		243179

Modified:
  stable/12/sbin/fsck_msdosfs/boot.c
Directory Properties:
  stable/12/   (props changed)

Modified: stable/12/sbin/fsck_msdosfs/boot.c
==============================================================================
--- stable/12/sbin/fsck_msdosfs/boot.c	Tue Jan 28 03:47:29 2020	(r357195)
+++ stable/12/sbin/fsck_msdosfs/boot.c	Tue Jan 28 07:49:52 2020	(r357196)
@@ -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 */
@@ -269,8 +269,11 @@ readboot(int dosfs, struct bootblock *boot)
 		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)
 		boot->ClustMask = CLUST32_MASK;
@@ -296,11 +299,19 @@ 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
+	 * 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;
@@ -342,7 +353,7 @@ writefsinfo(int dosfs, struct bootblock *boot)
 	 * 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.
 	 */