From d0657d01d7f29b36a03c72571762ad665552429b Mon Sep 17 00:00:00 2001
From: Ian Kelling <ian@iankelling.org>
Date: Sun, 15 Jan 2017 09:29:48 -0800
Subject: [PATCH] fix error handle path, add doc and cteate options

---
 newns | 125 ++++++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 99 insertions(+), 26 deletions(-)

diff --git a/newns b/newns
index 4fc887c..d60c0bc 100755
--- a/newns
+++ b/newns
@@ -14,17 +14,79 @@
 # limitations under the License.
 
 
-# Create a network namespace. Designed for use from systemd.
-
 [[ $EUID == 0 ]] || exec sudo -E "$BASH_SOURCE" "$@"
 
-cd "${BASH_SOURCE%/*}"
-source ../errhandle/errcatch-function
-source ../errhandle/bash-trace-function
-errcatch
+if [[ ! $ERRHANDLE_PATH ]]; then
+    ERRHANDLE_PATH=$(readlink -f "${BASH_SOURCE}")
+    ERRHANDLE_PATH=$(readlink -f ${ERRHANDLE_PATH%/*}/../errhandle)
+fi
+err_sourced=true
+for p in $ERRHANDLE_PATH/{errcatch-function,bash-trace-function}; do
+    if [[ -e $p ]]; then
+        source $p
+    else
+        err_sourced=false
+    fi
+done
+if $err_sourced; then
+    errcatch
+else
+    set -eE -o pipefail
+    trap 'echo "$0:$LINENO:error: \"$BASH_COMMAND\" returned $?" >&2' ERR
+fi
+
+usage() {
+    cat <<EOF
+usage: ${0##*/} [OPTS] start|stop NETNS_NAME
+
+-c, --create    Create network namespace. For running outside systemd private net.
+-h, --help      Show this help and exit.
+
+From within systemd network namespace, nat it to the outside.  If given
+-c, or if in the default network namespace, create a named network
+namepace natted to the current netns.
+
+Also create a named mount namespace under /root/mount_namespaces, so we
+can alter some system config for this namespace. Subsequent systemd
+command lines would be prefixed with:
+
+/usr/bin/nsenter --mount=/root/mount_namespaces/NETNS_NAME
+
+
+"ip netns new ..." also does a mount namespace, then bind mounts each
+thing in /etc/netns/NETNS_NAME to /etc/NETNS_NAME. Note, for openvpn having it's own
+resolv.conf, this doesn't help much. What we actually want to do is copy
+/run/resolvconf somehwere, then bind mount it on top of /run/resolvconf.
+
+Once systemd 233 comes out, it will have a bind mount option from within
+unit files, so the mount namespace won't be needed for this use case.
+
+Recommmended dependency of errhandle to print stack trace on error:
+https://iankelling.org/git/?p=errhandle, set ERRHANDLE_PATH, or put it
+in a directory adjacent to the absolute, resolved directory this file is
+in.
+
+EOF
+    exit ${1:-0}
+}
 
 
 ## begin arg parsing ##
+create=false
+temp=$(getopt -l help,create hc "$@") || usage 1
+eval set -- "$temp"
+while true; do
+    case $1 in
+        -c|--create) create=true; shift ;;
+        -h|--help) usage ;;
+        --) shift; break ;;
+        *) echo "$0: Internal error!" ; exit 1 ;;
+    esac
+done
+if (( $# != 2 )); then
+    usage 1
+fi
+
 action=$1
 nn=$2 # network namespace / namespace name
 ## end arg parsing ##
@@ -51,6 +113,9 @@ v0=veth0-$nn
 v1=veth1-$nn
 ip_base=10.173
 
+if ! $create && [[ $(readlink /proc/self/ns/net) == "$(readlink /proc/1/ns/net)" ]]; then
+    create=true
+fi
 
 target=/run/netns/default
 if [[ ! -e $target && ! -L $target ]]; then
@@ -61,18 +126,17 @@ fi
 
 
 ipd() { ip -n default "$@"; }
+if $create; then
+    ipnn() { ip -n $nn "$@"; }
+else
+    # we are already in the network namespace and it's unnamed.
+    ipnn() { ip "$@"; }
+fi
 dexec() { ip netns exec default "$@"; }
 
-# note: this script could be easily adapted to create a
-# netns instead of using the systemd created one.
-# ip netns add NAME
-# ip -n NAME link set dev lo up
-
-# random note, ip netns exec creates a mount namespace and
-# remaps /etc to /etc/netns/NAME.
 
-# head -n1 is defensive. I don't know if it's possible to have more
-# than one default route.
+# head -n1 is defensive. Not sure if there is some weird feature
+# for 2 routes to be 0/0.
 gateway_if=$(ipd route list exact 0/0 | head -n1| sed -r 's/.*\s(\S+)\s*$/\1/')
 nat() { dexec iptables -t nat $1 POSTROUTING -o $gateway_if -j MASQUERADE \
               -m comment --comment "systemd network namespace nat"; }
@@ -83,7 +147,7 @@ find_network() {
     ips="$(ipd addr show | awk '$1 == "inet" {print $2}')"
     for ((i=0; i <= 254; i++)); do
         network=$ip_base.$i
-        if printf "%s\n" "$ips" | grep "^${network//./\\.}"; then
+        if printf "%s\n" "$ips" | grep "^${network//./\\.}" >/dev/null; then
             existing=true
         else
             found=true
@@ -94,6 +158,12 @@ find_network() {
 
 start() {
 
+    find_network
+    if ! $found; then
+        echo "$0: error: no open network found"
+        exit 1
+    fi
+
     mkdir -p /root/mount_namespaces
     if ! mountpoint /root/mount_namespaces >/dev/null; then
         mount --bind /root/mount_namespaces /root/mount_namespaces
@@ -107,24 +177,24 @@ start() {
     fi
 
 
-
-    find_network
-    if ! $found; then
-        echo "$0: error: no open network found"
-        exit 1
+    if $create; then
+        ip netns add $nn
+        ip -n $nn link set dev lo up
     fi
 
+
+
     echo 1 | dexec dd of=/proc/sys/net/ipv4/ip_forward 2>/dev/null
 
     _errcatch_cleanup=stop
-    ip link add $v0 type veth peer name $v1
-    ip link set $v0 netns default
+    ipnn link add $v0 type veth peer name $v1
+    ipnn link set $v0 netns default
     ipd addr add $network.1/24 dev $v0
     ipd link set $v0 up
     nat -C &>/dev/null || nat -A
-    ip addr add $network.2/24 dev $v1
-    ip link set $v1 up
-    ip route add default via $network.1
+    ipnn addr add $network.2/24 dev $v1
+    ipnn link set $v1 up
+    ipnn route add default via $network.1
 
 }
 
@@ -137,6 +207,9 @@ stop() {
     if ! $existing; then
         if nat -C &>/dev/null; then nat -D; fi
     fi
+    if $create; then
+        ip netns del $nn
+    fi
 }
 
 case $action in
-- 
2.30.2