From 62d4fabc3bfd0d4e3debd20a6a2791c49c8bcab1 Mon Sep 17 00:00:00 2001
From: krw <krw@openbsd.org>
Date: Mon, 19 Jul 2021 14:30:08 +0000
Subject: [PATCH] Revert incorrect tweaks to disk geometry calculations and non
 '-b' MBR disk initialization.

Detected by bluhm@'s ever vigilant regress testing.
---
 sbin/fdisk/disk.c | 30 +++++++++++++++++-------------
 sbin/fdisk/mbr.c  | 16 +++++++++-------
 2 files changed, 26 insertions(+), 20 deletions(-)

diff --git a/sbin/fdisk/disk.c b/sbin/fdisk/disk.c
index 60a9d3d18a9..ee1111aee47 100644
--- a/sbin/fdisk/disk.c
+++ b/sbin/fdisk/disk.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: disk.c,v 1.67 2021/07/17 14:16:34 krw Exp $	*/
+/*	$OpenBSD: disk.c,v 1.68 2021/07/19 14:30:08 krw Exp $	*/
 
 /*
  * Copyright (c) 1997 Tobias Weingartner
@@ -64,29 +64,33 @@ DISK_open(const char *name, const int oflags)
 	/* Set geometry to use in MBR partitions. */
 	if (disk.dk_size > 0) {
 		/* -l has set disk size. */
-		sz = DL_BLKTOSEC(&dl, disk.dk_size);
+		sz = disk.dk_size;
 		disk.dk_heads = 1;
 		disk.dk_sectors = 64;
+		disk.dk_size = DL_BLKTOSEC(&dl, sz);
+		disk.dk_cylinders = disk.dk_size / disk.dk_sectors;
 	} else if (disk.dk_cylinders > 0) {
-		/* -c/-h/-c has set disk geometry. */
+		/* -c/-h/-s has set disk geometry & therefore size. */
 		sz = disk.dk_cylinders * disk.dk_heads * disk.dk_sectors;
-		sz = DL_BLKTOSEC(&dl, sz);
+		disk.dk_size = DL_BLKTOSEC(&dl, sz);
 		disk.dk_sectors = DL_BLKTOSEC(&dl, disk.dk_sectors);
 	} else {
-		sz = DL_GETDSIZE(&dl);
+		disk.dk_sectors = dl.d_nsectors;
+		disk.dk_cylinders = dl.d_ncylinders;
 		disk.dk_heads = dl.d_ntracks;
 		disk.dk_sectors = dl.d_nsectors;
+		/* MBR handles only first UINT32_MAX sectors. */
+		spc = (uint64_t)disk.dk_heads * disk.dk_sectors;
+		sz = DL_GETDSIZE(&dl);
+		if (sz > UINT32_MAX) {
+			disk.dk_cylinders = UINT32_MAX / spc;
+			disk.dk_size = disk.dk_cylinders * spc;
+		} else
+			disk.dk_size = sz;
 	}
 
-	if (sz > UINT32_MAX)
-		sz = UINT32_MAX;	/* MBR knows nothing > UINT32_MAX. */
-
-	spc = disk.dk_heads * disk.dk_sectors;
-	disk.dk_cylinders = sz / spc;
-	disk.dk_size = disk.dk_cylinders * spc;
-
 	if (disk.dk_size == 0)
-		errx(1, "dk_size == 0");
+		errx(1, "disk size is 0");
 
 	if (disk.dk_bootprt.prt_ns > 0) {
 		ns = disk.dk_bootprt.prt_ns + DL_BLKSPERSEC(&dl) - 1;
diff --git a/sbin/fdisk/mbr.c b/sbin/fdisk/mbr.c
index a13ccd6ae7d..22a10124290 100644
--- a/sbin/fdisk/mbr.c
+++ b/sbin/fdisk/mbr.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mbr.c,v 1.89 2021/07/18 21:40:13 krw Exp $	*/
+/*	$OpenBSD: mbr.c,v 1.90 2021/07/19 14:30:08 krw Exp $	*/
 
 /*
  * Copyright (c) 1997 Tobias Weingartner
@@ -132,12 +132,14 @@ MBR_init(struct mbr *mbr)
 	/* Fix up start/length fields */
 	PRT_fix_BN(&mbr->mbr_prt[3], 3);
 #else
-	mbr->mbr_prt[0] = disk.dk_bootprt;
-	PRT_fix_CHS(&mbr->mbr_prt[0]);
-	mbr->mbr_prt[3].prt_ns += mbr->mbr_prt[3].prt_bs;
-	mbr->mbr_prt[3].prt_bs = mbr->mbr_prt[0].prt_bs + mbr->mbr_prt[0].prt_ns;
-	mbr->mbr_prt[3].prt_ns -= mbr->mbr_prt[3].prt_bs;
-	PRT_fix_CHS(&mbr->mbr_prt[3]);
+	if (disk.dk_bootprt.prt_ns > 0) {
+		mbr->mbr_prt[0] = disk.dk_bootprt;
+		PRT_fix_CHS(&mbr->mbr_prt[0]);
+		mbr->mbr_prt[3].prt_ns += mbr->mbr_prt[3].prt_bs;
+		mbr->mbr_prt[3].prt_bs = mbr->mbr_prt[0].prt_bs + mbr->mbr_prt[0].prt_ns;
+		mbr->mbr_prt[3].prt_ns -= mbr->mbr_prt[3].prt_bs;
+		PRT_fix_CHS(&mbr->mbr_prt[3]);
+	}
 #endif
 
 	/* Start OpenBSD MBR partition on a power of 2 block number. */
-- 
2.20.1