From 910da6c68916ab2bf9c80093394ddab3e1d75172 Mon Sep 17 00:00:00 2001
From: Bruce Evans <bde@FreeBSD.org>
Date: Thu, 5 Feb 2004 15:18:18 +0000
Subject: [PATCH] Fixed some bugs in checkdirty().  The check for the clean bit
 was combined with the the signature check in a wrong way (basically (dirty:=
 signature_recognised() && !clean) instead of (mightbedirty:=
 !signature_recognized || !clean), so file systems with unrecognized
 signatures were considered clean.  Many of the don't-care and reserved bits
 were not ignored, so some file systems with valid signatures were
 unrecognized.  One of my FAT32 file systems has a signature of
 f8,ff,ff,ff,ff,ff,ff,f7 when dirty, but only f8,ff,ff,0f,ff,ff,ff,07 was
 recognised as dirty for FAT32, so the fail-unsafeness made my file system
 always considered clean.

Check the i/o non-error bit in checkdirty().  Its absence would give
an unrecognized signature in code that is unaware of it, but we now
mask it out of the signature so we have to check it explicitly.  This
combines naturally with the check of the clean bit.

Reviewed by:	rnordier (except for final details)
---
 sbin/fsck_msdosfs/fat.c | 36 +++++++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 9 deletions(-)

diff --git a/sbin/fsck_msdosfs/fat.c b/sbin/fsck_msdosfs/fat.c
index 55f9bbb80669..0b0bd9e11e89 100644
--- a/sbin/fsck_msdosfs/fat.c
+++ b/sbin/fsck_msdosfs/fat.c
@@ -77,7 +77,7 @@ checkdirty(int fs, struct bootblock *boot)
 	u_char *buffer;
 	int ret = 0;
 
-	if (boot->ClustMask == CLUST12_MASK)
+	if (boot->ClustMask != CLUST16_MASK && boot->ClustMask != CLUST32_MASK)
 		return 0;
 
 	off = boot->ResSectors;
@@ -99,14 +99,32 @@ checkdirty(int fs, struct bootblock *boot)
 		goto err;
 	}
 
-	if (buffer[0] == boot->Media && buffer[1] == 0xff && buffer[2] == 0xff
-	    && ((boot->ClustMask == CLUST16_MASK && buffer[3] == 0x7f)
-		|| (boot->ClustMask == CLUST32_MASK && buffer[3] == 0x0f
-		    && buffer[4] == 0xff && buffer[5] == 0xff
-		    && buffer[6] == 0xff && buffer[7] == 0x07)))
-		ret = 0;
-	else
-		ret = 1;
+	/*
+	 * If we don't understand the FAT, then the file system must be
+	 * assumed to be unclean.
+	 */
+	if (buffer[0] != boot->Media || buffer[1] != 0xff)
+		goto err;
+	if (boot->ClustMask == CLUST16_MASK) {
+		if ((buffer[2] & 0xf8) != 0xf8 || (buffer[3] & 0x3f) != 0x3f)
+			goto err;
+	} else {
+		if (buffer[2] != 0xff || (buffer[3] & 0x0f) != 0x0f
+		    || (buffer[4] & 0xf8) != 0xf8 || buffer[5] != 0xff
+		    || buffer[6] != 0xff || (buffer[7] & 0x03) != 0x03)
+			goto err;
+	}
+
+	/*
+	 * Now check the actual clean flag (and the no-error flag).
+	 */
+	if (boot->ClustMask == CLUST16_MASK) {
+		if ((buffer[3] & 0xc0) == 0xc0)
+			ret = 1;
+	} else {
+		if ((buffer[7] & 0x0c) == 0x0c)
+			ret = 1;
+	}
 
 err:
 	free(buffer);