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Improve shell style wrt. variable naming/boolean convention

The mixed use of upper and lower case variables is neither obvious nor
consistent.

PRINT_ONLY is local to netstart.
ip6kernel is local to netstart.
multicast gets sourced from rc.subr(8).

1. uppercase ip6kernel as is common for global variables in base scripts
2. use the simpler true/false idiom and default with the rest of
   netstart-only variables, making it clearer that only `multicast=YES/NO'
   comes from the rc environment
3. hoist kernel feature detection such that a later diff can load the SOII
   key conditionally
4. zap obvious comment

OK aja

#!/bin/sh -
#
#	$OpenBSD: netstart,v 1.223 2022/10/31 19:25:16 kn Exp $

# Turn off Strict Bourne shell mode.
set +o sh

# Show usage of the netstart script and exit.
usage() {
	print -u2 "usage: sh ${0##*/} [-n] [interface ...]"
	exit 1
}

# Test the first argument against the remaining ones, return success on a match.
isin() {
	local _a=$1 _b

	shift
	for _b; do
		[[ $_a == "$_b" ]] && return 0
	done
	return 1
}

# Echo file $1 to stdout. Skip comment lines. Strip leading and trailing
# whitespace if IFS is set.
# Usage: stripcom /path/to/file
stripcom() {
	local _file=$1 _line

	[[ -f $_file ]] || return

	while read _line; do
		[[ -n ${_line%%#*} ]] && print -r -- "$_line"
	done <$_file
}

# Parse and "unpack" a hostname.if(5) line given as positional parameters.
# Fill the _cmds array with the resulting interface configuration commands.
parse_hn_line() {
	local _af=0 _name=1 _mask=2 _bc=3 _prefix=2 _c _cmd _prev _daddr _dhcp _i
	set -A _c -- "$@"
	set -o noglob

	case ${_c[_af]} in
	''|*([[:blank:]])'#'*)
		return
		;;
	inet)	((${#_c[*]} > 1)) || return
		if [[ ${_c[_name]} == autoconf ]]; then
			_cmds[${#_cmds[*]}]="ifconfig $_if ${_c[@]}"
			V4_AUTOCONF=true
			return
		fi
		[[ ${_c[_name]} == alias ]] && _mask=3 _bc=4
		[[ -n ${_c[_mask]} ]] && _c[_mask]="netmask ${_c[_mask]}"
		if [[ -n ${_c[_bc]} ]]; then
			_c[_bc]="broadcast ${_c[_bc]}"
			[[ ${_c[_bc]} == *NONE ]] && _c[_bc]=
		fi
		_cmds[${#_cmds[*]}]="ifconfig $_if ${_c[@]}"
		;;
	inet6)	((${#_c[*]} > 1)) || return
		if [[ ${_c[_name]} == autoconf ]]; then
			_cmds[${#_cmds[*]}]="ifconfig $_if ${_c[@]}"
			V6_AUTOCONF=true
			return
		fi
		[[ ${_c[_name]} == alias ]] && _prefix=3
		[[ -n ${_c[_prefix]} ]] && _c[_prefix]="prefixlen ${_c[_prefix]}"
		_cmds[${#_cmds[*]}]="ifconfig $_if ${_c[@]}"
		;;
	dest)	((${#_c[*]} == 2)) && _daddr=${_c[1]} || return
		_prev=$((${#_cmds[*]} - 1))
		((_prev >= 0)) || return
		set -A _c -- ${_cmds[_prev]}
		_name=3
		[[ ${_c[_name]} == alias ]] && _name=4
		_c[_name]="${_c[_name]} $_daddr"
		_cmds[$_prev]="${_c[@]}"
		;;
	dhcp)	_cmds[${#_cmds[*]}]="ifconfig $_if inet autoconf"
		V4_AUTOCONF=true
		;;
	'!'*)	_cmd=$(print -- "${_c[@]}" | sed 's/\$if/'$_if'/g')
		_cmds[${#_cmds[*]}]="${_cmd#!}"
		;;
	*)	_cmds[${#_cmds[*]}]="ifconfig $_if ${_c[@]}"
		;;
	esac
	unset _c
	set +o noglob
}

# Create interface $1 if it does not yet exist.
# Usage: ifcreate if1
ifcreate() {
	local _if=$1

	if $PRINT_ONLY; then
		print -r -- "{ ifconfig $_if || ifconfig $_if create; }"
	else
		{ ifconfig $_if || ifconfig $_if create; } >/dev/null 2>&1
	fi
}

# Create interfaces for network pseudo-devices referred to by hostname.if files.
# Optionally, limit creation to given interfaces only.
# Usage: vifscreate [if ...]
vifscreate() {
	local _vif _hn _if

	for _vif in $(ifconfig -C); do
		for _hn in /etc/hostname.${_vif}+([[:digit:]]); do
			[[ -f $_hn ]] || continue
			_if=${_hn#/etc/hostname.}

			# loopback for routing domain is created by kernel
			[[ -n ${_if##lo[1-9]*} ]] || continue

			if (($# > 0)) && ! isin $_if "$@"; then
				continue
			fi

			if ! ifcreate $_if; then
				print -u2 "${0##*/}: create for '$_if' failed."
			fi
		done
	done
}

# Start a single interface.
# Usage: ifstart if1
ifstart() {
	local _if=$1 _hn=/etc/hostname.$1 _cmds _i=0 _line _stat
	set -A _cmds

	# Interface names must be alphanumeric only.  We check to avoid
	# configuring backup or temp files, and to catch the "*" case.
	[[ $_if != +([[:alpha:]])+([[:digit:]]) ]] && return

	if [[ ! -f $_hn ]]; then
		print -u2 "${0##*/}: $_hn: No such file or directory."
		return
	fi

	# Not using stat(1), we can't rely on having /usr yet.
	set -A _stat -- $(ls -nL $_hn)
	if [[ "${_stat[0]}${_stat[2]}${_stat[3]}" != *---00 ]]; then
		print -u2 "WARNING: $_hn is insecure, fixing permissions."
		chmod -LR o-rwx $_hn
		chown -LR root:wheel $_hn
	fi

	# Check for ifconfig'able interface, except if -n option is specified.
	ifcreate $_if || return

	# Parse the hostname.if(5) file and fill _cmds array with interface
	# configuration commands.
	set -o noglob
	while IFS= read -- _line; do
		parse_hn_line $_line
	done <$_hn

	# Apply the interface configuration commands stored in _cmds array.
	while ((_i < ${#_cmds[*]})); do
		if $PRINT_ONLY; then
			print -r -- "${_cmds[_i]}"
		else
			eval "${_cmds[_i]}"
		fi
		((_i++))
	done
	unset _cmds
	set +o noglob
}

# Start multiple interfaces by driver name.
# Usage: ifmstart "em iwm" "trunk vlan"
#   Start "$1" interfaces in order or all interfaces if empty.
#   Don't start "$2" interfaces. "$2" is optional.
ifmstart() {
	local _sifs=$1 _xifs=$2 _hn _if _sif _xif

	for _sif in ${_sifs:-ALL}; do
		for _hn in /etc/hostname.+([[:alpha:]])+([[:digit:]]); do
			[[ -f $_hn ]] || continue
			_if=${_hn#/etc/hostname.}

			# Skip unwanted ifs.
			for _xif in $_xifs; do
				[[ $_xif == ${_if%%[0-9]*} ]] && continue 2
			done

			# Start wanted ifs.
			[[ $_sif == @(ALL|${_if%%[0-9]*}) ]] && ifstart $_if
		done
	done
}

# Parse /etc/mygate and add default routes for IPv4 and IPv6.
# Usage: defaultroute
defaultroute() {
	local _cmd _v4set=false _v6set=false;
	set -o noglob

	stripcom /etc/mygate |
	while read gw; do
		case $gw in
		'!'*)
			_cmd=$(print -- "$gw")
			_cmd="${_cmd#!}"
			;;
		!(*:*))
			($_v4set || $V4_AUTOCONF) && continue
			_cmd="route -qn add -host default $gw"
			_v4set=true
			;;
		*)
			($_v6set || $V6_AUTOCONF) && continue
			_cmd="route -qn add -host -inet6 default $gw"
			_v6set=true
			;;
		esac
		if $PRINT_ONLY; then
			print -r -- "$_cmd"
		else
			$_cmd
		fi
	done
	set +o noglob
}

# add all the routes needed for IPv6
ip6routes() {
	local _i=0
	set -A _cmds

	# Disallow link-local unicast dest without outgoing scope identifiers.
	_cmds[_i++]="route -qn add -inet6 fe80:: -prefixlen 10 ::1 -reject"

	# Disallow site-local unicast dest without outgoing scope identifiers.
	# If you configure site-locals without scope id (it is permissible
	# config for routers that are not on scope boundary), you may want
	# to comment the line out.
	_cmds[_i++]="route -qn add -inet6 fec0:: -prefixlen 10 ::1 -reject"

	# Disallow "internal" addresses to appear on the wire.
	_cmds[_i++]="route -qn add -inet6 ::ffff:0.0.0.0 -prefixlen 96 ::1 -reject"

	# Disallow packets to malicious 6to4 prefix.
	_cmds[_i++]="route -qn add -inet6 2002:e000:: -prefixlen 20 ::1 -reject"
	_cmds[_i++]="route -qn add -inet6 2002:7f00:: -prefixlen 24 ::1 -reject"
	_cmds[_i++]="route -qn add -inet6 2002:0000:: -prefixlen 24 ::1 -reject"
	_cmds[_i++]="route -qn add -inet6 2002:ff00:: -prefixlen 24 ::1 -reject"

	# Disallow packets without scope identifier.
	_cmds[_i++]="route -qn add -inet6 ff01:: -prefixlen 16 ::1 -reject"
	_cmds[_i++]="route -qn add -inet6 ff02:: -prefixlen 16 ::1 -reject"

	# Completely disallow packets to IPv4 compatible prefix.
	#
	# This may conflict with RFC1933 under following circumstances:
	# (1) An IPv6-only KAME node tries to originate packets to IPv4
	#     compatible destination.  The KAME node has no IPv4 compatible
	#     support.  Under RFC1933, it should transmit native IPv6
	#     packets toward IPv4 compatible destination, hoping it would
	#     reach a router that forwards the packet toward auto-tunnel
	#     interface.
	# (2) An IPv6-only node originates a packet to an IPv4 compatible
	#     destination.  A KAME node is acting as an IPv6 router, and
	#     asked to forward it.
	#
	# Due to rare use of IPv4 compatible addresses, and security issues
	# with it, we disable it by default.
	_cmds[_i++]="route -qn add -inet6 ::0.0.0.0 -prefixlen 96 ::1 -reject"

	# Apply the interface configuration commands stored in _cmds array.
	_i=0
	while ((_i < ${#_cmds[*]})); do
		if $PRINT_ONLY; then
			print -r -- "${_cmds[_i]}"
		else
			eval "${_cmds[_i]}"
		fi
		((_i++))
	done
	unset _cmds
}

# wait for autoconf interfaces
wait_autoconf_default() {
	if ifconfig | grep -q ': flags=.*<.*AUTOCONF.*>'; then
		count=0
		while ((count++ < 20)); do
			route -n show | grep -q ^default && break
			sleep .5
		done
	fi
}

# Make sure the invoking user has the right privileges.  Check for presence of
# id(1) to avoid problems with diskless setups.
if [[ -x /usr/bin/id ]] && (($(id -u) != 0)); then
	echo "${0##*/}: need root privileges"
	exit 1
fi

# Get network related vars from rc.conf using the parsing routine from rc.subr.
FUNCS_ONLY=1 . /etc/rc.d/rc.subr
_rc_parse_conf

PRINT_ONLY=false
V4_AUTOCONF=false
V6_AUTOCONF=false
IP6KERNEL=false

while getopts ":n" opt; do
	case $opt in
	n)	PRINT_ONLY=true;;
	*)	usage;;
	esac
done
shift $((OPTIND-1))

if ifconfig lo0 inet6 >/dev/null 2>&1; then
	IP6KERNEL=true
	ip6routes
fi

# Load key material for the generation of IPv6 Semantically Opaque Interface
# Identifiers (SOII) used for link local and SLAAC addresses.
$PRINT_ONLY || [[ ! -f /etc/soii.key ]] ||
	sysctl -q "net.inet6.ip6.soiikey=$(</etc/soii.key)"

# If we were invoked with a list of interface names, just reconfigure these
# interfaces (or bridges), add default routes and return.
# Create virtual interfaces upfront to make ifconfig commands depending on
# other interfaces, e.g. "patch", work regardless of in which order interface
# names were specified.
if (($# > 0)); then
	vifscreate "$@"
	for _if; do ifstart $_if; done
	defaultroute
	return
fi

# Otherwise, process with the complete network initialization.

# Set the address for the loopback interface.  Bringing the interface up,
# automatically invokes the IPv6 address ::1.
if $PRINT_ONLY; then
	print -r -- "ifconfig lo0 inet 127.0.0.1/8"
else
	ifconfig lo0 inet 127.0.0.1/8
fi

# Create all the pseudo interfaces up front.
vifscreate

# Configure all the non-loopback interfaces which we know about, but
# do not start interfaces which must be delayed. Refer to hostname.if(5)
ifmstart "" "aggr trunk svlan vlan carp pppoe tun tap gif etherip gre egre nvgre eoip vxlan pflow wg"

# The aggr and trunk interfaces need to come up first in this list.
# The (s)vlan interfaces need to come up after trunk.
# Configure all the carp interfaces which we know about before default route.
ifmstart "aggr trunk svlan vlan carp pppoe"

# Set default routes for IPv4 and IPv6.
defaultroute

# Multicast routing.
if [[ $multicast != YES ]]; then
	if $PRINT_ONLY; then
		print -r -- "route -qn delete 224.0.0.0/4"
		print -r -- "route -qn add -net 224.0.0.0/4 -interface 127.0.0.1 -reject"
	else
		route -qn delete 224.0.0.0/4
		route -qn add -net 224.0.0.0/4 -interface 127.0.0.1 -reject
	fi
fi

# Reject 127/8 other than 127.0.0.1.
if $PRINT_ONLY; then
	print -r -- "route -qn add -net 127 127.0.0.1 -reject"
else
	route -qn add -net 127 127.0.0.1 -reject
fi

# If interface autoconf exists, pause a little for at least one default route
$PRINT_ONLY || wait_autoconf_default

# Configure interfaces that rely on routing
ifmstart "tun tap gif etherip gre egre nvgre eoip vxlan pflow wg"

if $IP6KERNEL; then
	# Ensure IPv6 Duplicate Address Detection (DAD) is completed.
	count=0
	while ((count++ < 10 && $(sysctl -n net.inet6.ip6.dad_pending) != 0)); do
		sleep 1
	done
fi