From ca887f8d070d0bd2da705d10b9719d50b702f134 Mon Sep 17 00:00:00 2001
From: Baptiste Daroussin <bapt@FreeBSD.org>
Date: Tue, 5 May 2015 09:29:32 +0000
Subject: [PATCH] Ensure we read existing values of the stk table

Obtained from:	NetBSD
---
 usr.bin/checknr/checknr.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/usr.bin/checknr/checknr.c b/usr.bin/checknr/checknr.c
index 01d3216afc5..c150b795e41 100644
--- a/usr.bin/checknr/checknr.c
+++ b/usr.bin/checknr/checknr.c
@@ -341,7 +341,8 @@ process(FILE *f)
 						n = 10 * n + line[i] - '0';
 					i--;
 					if (n == 0) {
-						if (stk[stktop].opno == SZ) {
+						if (stktop >= 0 &&
+						    stk[stktop].opno == SZ) {
 							stktop--;
 						} else {
 							pe(lineno);
@@ -356,7 +357,8 @@ process(FILE *f)
 				} else if (!fflag && line[i] == 'f') {
 					n = line[++i];
 					if (n == 'P') {
-						if (stk[stktop].opno == FT) {
+						if (stktop >= 0 && 
+						    stk[stktop].opno == FT) {
 							stktop--;
 						} else {
 							pe(lineno);