From da5825f8edbd35665f1d20d0756fa1af2747487c Mon Sep 17 00:00:00 2001
From: cnst <cnst@NetBSD.org>
Date: Mon, 30 Sep 2019 23:23:59 +0000
Subject: [PATCH] kern/subr_disk: bounds_check_with_label: really protect
 against div by zero

Solves kernel panic in NetBSD 8.1 amd64 on VirtualBox 6.0.12 r133076.

Triggered with an NVMe controller without any actual discs behind it:

nvme0 at pci0 dev 14 function 0: vendor 80ee product 4e56 (rev. 0x00)
nvme0: NVMe 1.2
nvme0: interrupting at ioapic0 pin 22
nvme0: ORCL-VBOX-NVME-VER12, firmware 1.0, serial VB1234-56789
ld0 at nvme0 nsid 1
ld0: 0, 0 cyl, 16 head, 63 sec, 1 bytes/sect x 0 sectors

Code path is reached 4 times during normal boot, each time after wd0a
is already mounted; this patch avoids a crash with a dirty filesystem.
---
 sys/kern/subr_disk.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/sys/kern/subr_disk.c b/sys/kern/subr_disk.c
index 1e2a2dafa9a1..06e70d5e60f1 100644
--- a/sys/kern/subr_disk.c
+++ b/sys/kern/subr_disk.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: subr_disk.c,v 1.128 2019/05/22 08:47:02 hannken Exp $	*/
+/*	$NetBSD: subr_disk.c,v 1.129 2019/09/30 23:23:59 cnst Exp $	*/
 
 /*-
  * Copyright (c) 1996, 1997, 1999, 2000, 2009 The NetBSD Foundation, Inc.
@@ -67,7 +67,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: subr_disk.c,v 1.128 2019/05/22 08:47:02 hannken Exp $");
+__KERNEL_RCSID(0, "$NetBSD: subr_disk.c,v 1.129 2019/09/30 23:23:59 cnst Exp $");
 
 #include <sys/param.h>
 #include <sys/kernel.h>
@@ -385,7 +385,7 @@ bounds_check_with_label(struct disk *dk, struct buf *bp, int wlabel)
 	}
 
 	/* Protect against division by zero. XXX: Should never happen?!?! */
-	if (lp->d_secpercyl == 0) {
+	if ((lp->d_secsize / DEV_BSIZE) == 0 || lp->d_secpercyl == 0) {
 		bp->b_error = EINVAL;
 		return -1;
 	}