Introduce an example script of safe changing of ipfw(8) rules.

I'm sure this can be much improved, but this works fairly well.

PR:		27887
Submitted by:	Alexandre Peixoto <alexandref@tcoip.com.br>
MFC after:	1 week

share/examples/ipfw/change_rules.sh

@@ -0,0 +1,114 @@
+#!/bin/sh
+#
+# Copyright (c) 2000 Alexandre Peixoto
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+#
+# $FreeBSD$
+
+# Change ipfw(8) rules with safety guarantees for remote operation
+#
+# Invoke this script to edit rc.firewall. It will call ${EDITOR}, or
+# vi(1) if the environment variable is not set, for you to edit rc.firewall,
+# asks for confirmation and then run rc.firewall. You can then examine
+# the output of ipfw list and confirm whether you want the new version or
+# not.
+#
+# If no answer is received in 30 seconds, the previous rc.firewall is
+# run, restoring the old rules (this assumes ipfw flush is present in
+# it).
+#
+# If the new rules are confirmed, they'll replace rc.firewall and the
+# previous ones will be copied to rc.firewall.{date}. A mail will also
+# be sent to root with the unified diffs of the rule change.
+#
+# Non-approved rules are kept in rc.firewall.new, and you are offered
+# the option of changing them instead of the present rules when you
+# call this script.
+#
+# It is suggested improving this script by using some version control
+# software.
+
+get_yes_no() {
+	while true
+	do
+		echo -n "$1 (Y/N) ? " 
+		read -t 30 a
+		if [ $? != 0 ]; then
+			a="No";
+		        return;
+		fi
+		case $a in
+			[Yy]) a="Yes";
+			      return;;
+			[Nn]) a="No";
+			      return;;
+			*);;
+		esac
+	done
+}
+
+restore_rules() {
+	nohup sh /etc/rc.firewall >/dev/null 2>&1 
+	exit
+}
+
+if [ -f /etc/rc.firewall.new ]; then
+	get_yes_no "A new rules file already exists, do you want to use it"
+	[ $a = 'No' ] && cp /etc/rc.firewall /etc/rc.firewall.new
+else 
+	cp /etc/rc.firewall /etc/rc.firewall.new
+fi
+
+trap restore_rules SIGHUP
+
+vi /etc/rc.firewall.new
+
+get_yes_no "Do you want to install the new rules"
+
+[ $a = 'No' ] && exit
+
+cat <<!
+The rules will be changed now. If the message 'Type y to keep the new rules'
+do not appear on the screen or the y key is not pressed in 30 seconds, the
+former rules will be restored.
+The TCP/IP connections might be broken during the change. If so, restore
+the ssh/telnet connection being used.
+!
+
+nohup sh /etc/rc.firewall.new > /tmp/rc.firewall.out 2>&1;
+sleep 2;
+get_yes_no "Would you like to see the resulting new rules"
+[ $a = 'Yes' ] && vi /tmp/rc.firewall.out
+get_yes_no "Type y to keep the new rules"
+[ $a != 'Yes' ] && restore_rules
+
+DATE=`date "+%Y%m%d%H%M"`
+cp /etc/rc.firewall /etc/rc.firewall.$DATE
+mv /etc/rc.firewall.new /etc/rc.firewall
+cat <<!
+The new rules are now default. The previous rules have been preserved
+in the file /etc/rc.firewall.$DATE
+!
+diff -F "^# .*[A-Za-z]" -u /etc/rc.firewall.$DATE /etc/rc.firewall | mail -s "`hostname` Firewall rule change" root
+