slirp4netns.sh: Introduce compatibility wrapper behaving like slirp4netns(1)

Warning: draft quality, not really tested, --enable-sandbox not
supported yet.

Example:

 $ unshare -rUn
 # echo $$
 3130879

 $ ./slirp4netns.sh -m 65520 -c 3130879 tap0
 sent tapfd=5 for tap0
 received tapfd=5
 Starting slirp
 * MTU:             65520
 * Network:         10.0.2.0
 * Netmask:         255.255.255.0
 * Gateway:         10.0.2.2
 * DNS:             10.0.2.3
 * Recommended IP:  10.0.2.100
 WARNING: 127.0.0.1:* on the host is accessible as 10.0.2.2 (set --disable-host-loopback to prohibit connecting to 127.0.0.1:*)

 # ip li sh
 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
 33: tap0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65520 qdisc pfifo_fast state UNKNOWN mode DEFAULT group default qlen 1000
     link/ether 5e:9d:a0:c5:cf:67 brd ff:ff:ff:ff:ff:ff
 # ip ad sh
 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
     inet 127.0.0.1/8 scope host lo
        valid_lft forever preferred_lft forever
     inet6 ::1/128 scope host
        valid_lft forever preferred_lft forever
 33: tap0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65520 qdisc pfifo_fast state UNKNOWN group default qlen 1000
     link/ether 5e:9d:a0:c5:cf:67 brd ff:ff:ff:ff:ff:ff
     inet 10.0.2.0/24 scope global tap0
        valid_lft forever preferred_lft forever
     inet6 fe80::5c9d:a0ff:fec5:cf67/64 scope link
        valid_lft forever preferred_lft forever
 # ip ro sh
 default via 10.0.2.2 dev tap0
 10.0.2.0/24 dev tap0 proto kernel scope link src 10.0.2.0
 root@epycfail:~# ip -6 ro sh
 fe80::/64 dev tap0 proto kernel metric 256 pref medium
 # iperf3 -c 10.0.2.2 -l1M
 Connecting to host 10.0.2.2, port 5201
 [  5] local 10.0.2.0 port 43014 connected to 10.0.2.2 port 5201
 [ ID] Interval           Transfer     Bitrate         Retr  Cwnd
 [  5]   0.00-1.00   sec  1.38 GBytes  11.8 Gbits/sec    0   9.96 MBytes
 [  5]   1.00-2.00   sec  1.59 GBytes  13.6 Gbits/sec    0   13.3 MBytes
 [  5]   2.00-3.00   sec  1.63 GBytes  14.0 Gbits/sec    0   13.3 MBytes
 [  5]   3.00-4.00   sec  1.78 GBytes  15.3 Gbits/sec    0   13.3 MBytes
 [  5]   4.00-5.00   sec  1.80 GBytes  15.5 Gbits/sec    0   15.8 MBytes
 [  5]   5.00-6.00   sec  1.69 GBytes  14.5 Gbits/sec    0   15.8 MBytes
 [  5]   6.00-7.00   sec  1.65 GBytes  14.2 Gbits/sec    0   15.8 MBytes
 [  5]   7.00-8.00   sec  1.68 GBytes  14.4 Gbits/sec    0   15.8 MBytes
 [  5]   8.00-9.00   sec  1.60 GBytes  13.7 Gbits/sec    0   15.8 MBytes
 [  5]   9.00-10.00  sec  1.66 GBytes  14.3 Gbits/sec    0   15.8 MBytes
 - - - - - - - - - - - - - - - - - - - - - - - - -
 [ ID] Interval           Transfer     Bitrate         Retr
 [  5]   0.00-10.00  sec  16.5 GBytes  14.1 Gbits/sec    0             sender
 [  5]   0.00-10.01  sec  16.4 GBytes  14.1 Gbits/sec                  receiver

 iperf Done.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 227 insertions, 0 deletions

diff --git a/slirp4netns.sh b/slirp4netns.sh
new file mode 100755
index 0000000..f543e9b
--- /dev/null
+++ b/slirp4netns.sh
@@ -0,0 +1,227 @@
+#!/bin/sh -euf
+#
+# SPDX-License-Identifier: AGPL-3.0-or-later
+#
+# PASST - Plug A Simple Socket Transport
+#  for qemu/UNIX domain socket mode
+#
+# PASTA - Pack A Subtle Tap Abstraction
+#  for network namespace/tap device mode
+#
+# slirp4netns.sh - Compatibility wrapper for pasta, behaving like slirp4netns(1)
+#
+# WARNING: Draft quality, not really tested, --enable-sandbox not supported yet
+#
+# Copyright (c) 2021 Red Hat GmbH
+# Author: Stefano Brivio <sbrivio@redhat.com>
+
+PASTA_PID="$(mktemp)"
+PASTA_OPTS="-q --ipv4-only -a 10.0.2.0 -n 24 -g 10.0.2.2 -m 1500 --no-ndp --no-dhcpv6 --no-dhcp -P ${PASTA_PID}"
+
+# add() - Add single option to $PASTA_OPTS
+# $1:	Option name, with or without argument
+add() {
+	PASTA_OPTS="${PASTA_OPTS} ${1}"
+}
+
+# drop() - Drop one option (without argument) from $PASTA_OPTS
+# $1:	Option name
+drop() {
+	old_opts="${PASTA_OPTS}"; PASTA_OPTS=
+	for o in ${old_opts}; do [ "${o}" != "${1}" ] && add "${o}"; done
+}
+
+# sub() - Substitute option in $PASTA_OPTS, with or without argument
+# $1:	Option name
+# $2:	Option argument, can be empty
+sub() {
+	old_opts="${PASTA_OPTS}"; PASTA_OPTS=
+	next=0
+	for o in ${old_opts}; do
+		if [ ${next} -eq 1 ]; then
+			next=0; add "${1} ${2}"; shift; shift; continue
+		fi
+
+		for r in ${@}; do [ "${o}" = "${r}" ] && next=1 && break; done
+		[ "${next}" -eq 0 ] && add "${o}"
+	done
+}
+
+# xorshift() - pseudorandom permutation of 16-bit group
+# $1:	16-bit value to shuffle
+xorshift() {
+	# Adaptation of Xorshift algorithm from:
+	#   Marsaglia, G. (2003). Xorshift RNGs.
+	#   Journal of Statistical Software, 8(14), 1 - 6.
+	#   doi:http://dx.doi.org/10.18637/jss.v008.i14
+	# with triplet (5, 3, 1), suitable for 16-bit ranges.
+	n=${1}
+	: $((n ^= n << 5))
+	: $((n ^= n >> 3))
+	: $((n ^= n << 1))
+	echo ${n}
+}
+
+# opt() - Validate single option from getopts
+# $1:	Option type
+# $@:	Variable names to assign to
+opt() {
+	case "${1}" in
+	u32)
+		if ! printf "%i" "${OPTARG}" >/dev/null 2>&1 || \
+		   [ "${OPTARG}" -lt 0 ]; then
+			echo "${OPT} must be a non-negative integer"
+			usage
+		fi
+		eval ${2}="${OPTARG}"
+		;;
+	mtu)
+		if ! printf "%i" "${OPTARG}" >/dev/null 2>&1 || \
+		   [ "${OPTARG}" -lt 0 ] || [ "${OPTARG}" -ge 65522 ]; then
+			echo "MTU must be a positive integer (< 65522)"
+			usage
+		fi
+		eval ${2}="${OPTARG}"
+		;;
+	str)
+		eval ${2}="${OPTARG}"
+		;;
+	net4)
+		addr="${OPTARG%/*}"
+		mask="${OPTARG##*/}"
+
+		{ [ -z "${mask}" ] || !printf "%i" "${mask}" >/dev/null 2>&1 \
+		  || [ ${mask} -gt 32 ] || ${mask} -le 0 ]; } && usage
+
+		expr "${addr}" :					      \
+			'[0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*$' \
+			>/dev/null
+		[ $? -ne 0 ] && usage
+
+		ifs="${IFS}"; IFS='.'
+		for q in ${addr}; do [ ${q} -gt 255 ] && usage; done
+		IFS="${ifs}"
+
+		eval ${2}="${addr}"
+		eval ${3}="${mask}"
+		;;
+	esac
+}
+
+# usage() - Print slirpnetns(1) usage and exit indicating failure
+# $1:	Invalid option name, if any
+usage() {
+	[ ${#} -eq 1 ] && printf "s: invalid option -- '%s'\n" "${0}" "${1}"
+	cat << EOF
+Usage: ${0} [OPTION]... PID|PATH TAPNAME
+User-mode networking for unprivileged network namespaces.
+
+-c, --configure          bring up the interface
+-e, --exit-fd=FD         specify the FD for terminating slirp4netns
+-r, --ready-fd=FD        specify the FD to write to when the network is configured
+-m, --mtu=MTU            specify MTU (default=1500, max=65521)
+-6, --enable-ipv6        enable IPv6 (experimental)
+-a, --api-socket=PATH    specify API socket path
+--cidr=CIDR              specify network address CIDR (default=10.0.2.0/24)
+--disable-host-loopback  prohibit connecting to 127.0.0.1:* on the host namespace
+--netns-type=TYPE 	 specify network namespace type ([path|pid], default=pid)
+--userns-path=PATH	 specify user namespace path
+--enable-sandbox         create a new mount namespace (and drop all caps except CAP_NET_BIND_SERVICE if running as the root)
+--enable-seccomp         enable seccomp to limit syscalls (experimental)
+-h, --help               show this help and exit
+-v, --version            show version and exit
+EOF
+	exit 1
+}
+
+# version() - Print version
+version() {
+	echo "slirp4netns-like wrapper for pasta"
+	exit 0
+}
+
+# gen_addr6() - Generate pseudorandom IPv6 address, changes every second
+gen_addr6() {
+	printf "fd00"
+	n=$(($(xorshift $(date +%S)) % 65536))
+	for i in $(seq 2 8); do
+		printf ":%04x" ${n}
+		n=$(($(xorshift ${n}) % 65536))
+	done
+}
+
+# Default options
+v6=0
+get_pid=0
+MTU=1500
+A4="10.0.2.0"
+M4="255.255.255.0"
+no_map_gw=0
+EFD=0
+RFD=0
+
+while getopts ce:r:m:6a:hv-: OPT 2>/dev/null; do
+	if [ "${OPT}" = "-" ]; then
+		OPT="${OPTARG%%[= ]*}"
+		OPTARG="${OPTARG#${OPT}[= ]}"
+	fi
+	case "${OPT}" in
+	c | configure)		add "--config-net"			      ;;
+	e | exit-fd)		opt u32 EFD				      ;;
+	r | ready-fd)		opt u32 RFD				      ;;
+	m | mtu)		opt mtu MTU && sub -m ${MTU}		      ;;
+	6 | enable-ipv6)	V6=1					      ;;
+	a | api-socket)		opt str API				      ;;
+	cidr)			opt net4 A4 M4 && sub -a ${A4} -n ${M4}	      ;;
+	disable-host-loopback)	add "--no-map-gw" && no_map_gw=1	      ;;
+	netns-type)		: Autodetected				      ;;
+	userns-path)		opt_str USERNS_NAME "${OPTARG}"		      ;;
+	enable-sandbox) 	: Not supported yet			      ;;
+	enable-seccomp)		: Cannot be disabled			      ;;
+	h | help)		usage "${0}"				      ;;
+	v | version)		version					      ;;
+	??*)			usage "${0}" "${OPT}"			      ;;
+	?)			usage "${0}"				      ;;
+	esac
+done
+
+shift $((OPTIND - 1))
+[ ${#} -ne 2 ] && usage
+ns_spec="${1}"
+
+ifname="${2}"
+add "-I ${ifname}"
+
+if [ ${v6} -eq 1 ]; then
+	drop "--ipv4-only"
+	add "-a $(gen_addr6) -g fd00::2 -D fd00::3"
+fi
+
+./pasta ${PASTA_OPTS} ${ns_spec} 2>/dev/null && \
+	[ ${RFD} -ne 0 ] && echo "1" >&${RFD}
+
+trap "kill $(cat ${PASTA_PID}); rm ${PASTA_PID}" INT TERM
+
+cat << EOF
+sent tapfd=5 for ${ifname}
+received tapfd=5
+Starting slirp
+* MTU:             ${MTU}
+* Network:         ${A4}
+* Netmask:         ${M4}
+* Gateway:         10.0.2.2
+* DNS:             10.0.2.3
+* Recommended IP:  10.0.2.100
+EOF
+
+if [ ${no_map_gw} -eq 0 ]; then
+	echo "WARNING: 127.0.0.1:* on the host is accessible as 10.0.2.2 (set --disable-host-loopback to prohibit connecting to 127.0.0.1:*)"
+fi
+
+if [ ${EFD} -ne 0 ]; then
+	dd count=1 of=/dev/null 2>/dev/null <&${EFD}
+else
+	while read a; do :; done
+fi
+
+exit 0