From a41642971dfc8a4865f478960586a4a706406bd0 Mon Sep 17 00:00:00 2001
From: krw <krw@openbsd.org>
Date: Mon, 25 Aug 2008 11:27:00 +0000
Subject: [PATCH] If partoffp is non-NULL then readdoslabel() is just looking
 for the correct address to write the passed label. Don't spoof partitions
 while looking for the address, as this could result in an invalid label being
 written out.

"That looks right" deraadt@ "Looks good to me" miod@
---
 sys/kern/subr_disk.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/sys/kern/subr_disk.c b/sys/kern/subr_disk.c
index cb0d89338fd..5668686cb31 100644
--- a/sys/kern/subr_disk.c
+++ b/sys/kern/subr_disk.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: subr_disk.c,v 1.81 2008/08/22 03:19:02 deraadt Exp $	*/
+/*	$OpenBSD: subr_disk.c,v 1.82 2008/08/25 11:27:00 krw Exp $	*/
 /*	$NetBSD: subr_disk.c,v 1.17 1996/03/16 23:17:08 christos Exp $	*/
 
 /*
@@ -447,6 +447,7 @@ donot:
 		 */
 		for (dp2=dp, i=0; i < NDOSPART && n < 8; i++, dp2++) {
 			struct partition *pp = &lp->d_partitions[8+n];
+			u_int8_t fstype;
 
 			if (dp2->dp_typ == DOSPTYP_OPENBSD)
 				continue;
@@ -459,17 +460,17 @@ donot:
 
 			switch (dp2->dp_typ) {
 			case DOSPTYP_UNUSED:
-				pp->p_fstype = FS_UNUSED;
+				fstype = FS_UNUSED;
 				n++;
 				break;
 
 			case DOSPTYP_LINUX:
-				pp->p_fstype = FS_EXT2FS;
+				fstype = FS_EXT2FS;
 				n++;
 				break;
 
 			case DOSPTYP_NTFS:
-				pp->p_fstype = FS_NTFS;
+				fstype = FS_NTFS;
 				n++;
 				break;
 
@@ -479,7 +480,7 @@ donot:
 			case DOSPTYP_FAT16L:
 			case DOSPTYP_FAT32:
 			case DOSPTYP_FAT32L:
-				pp->p_fstype = FS_MSDOS;
+				fstype = FS_MSDOS;
 				n++;
 				break;
 			case DOSPTYP_EXTEND:
@@ -492,25 +493,30 @@ donot:
 				wander = 1;
 				break;
 			default:
-				pp->p_fstype = FS_OTHER;
+				fstype = FS_OTHER;
 				n++;
 				break;
 			}
 
 			/*
-			 * There is no need to set the offset/size when
-			 * wandering; it would also invalidate the
-			 * disklabel checksum.
+			 * Don't set fstype/offset/size when wandering or just
+			 * looking for the offset of the OpenBSD partition. It
+			 * would invalidate the disklabel checksum!
 			 */
-			if (wander)
+			if (wander || partoffp)
 				continue;
 
+			pp->p_fstype = fstype;
 			if (letoh32(dp2->dp_start))
 				DL_SETPOFFSET(pp,
 				    letoh32(dp2->dp_start) + part_blkno);
 			DL_SETPSIZE(pp, letoh32(dp2->dp_size));
 		}
 	}
+	if (partoffp)
+		/* dospartoff has been set and we must not modify *lp. */
+		goto notfat;
+
 	lp->d_npartitions = MAXPARTITIONS;
 
 	if (n == 0 && part_blkno == DOSBBSECTOR) {
-- 
2.20.1