reversetether.sh

#!/bin/bash
# enables reverse tether on android phones
# requires networkmanager
# tested & developed with CM12 (Android 5.1.1)

ADB=adb
# get by nmcli list
NM_CONN="048202e0-a62c-431b-8fc1-cf8fd552343e"
# the rndis device on your phone (adb shell ip link)
IF=usb0
WLANIF=wlan0

adb_root() {
    $ADB shell "su -c '$1'"
}

adb_shell() {
    $ADB shell "$1"
}

adb_wait() {
    $ADB wait-for-device
}

info() {
    echo -e "[\e[94m*\e[0m] $1"
}

warn() {
    echo -e "[\e[93m~\e[0m] $1"
}

error() {
    echo -e "[\e[91m!\e[0m] $1"
}

fatal() {
    error "$1"
    exit 1
}

success() {
    echo -e "[\e[92m+\e[0m] $1"
}


setup_device_net() {
    info "Enabled usb net"
    adb_root 'setprop sys.usb.config rndis,adb'
    adb_wait
    success "Device back up"

    adb_root "ip addr add 10.42.0.2/24 dev $IF"
    adb_root "ip link set $IF up"
    adb_root "ip route add default via 10.42.0.1"
}

setup_host_net() {
    info "Starting connection"
    (nmcli con up $NM_CONN && success "connected") || fatal "Couldn't start connection"

    info "Setup iptables"
    sudo iptables -t nat -F
    sudo iptables -t nat -A POSTROUTING -j MASQUERADE
    sudo sysctl -w net.ipv4.ip_forward=1
    success "DONE"
}

fix_routes() {
    adb_root "ip route delete default table $1"
    adb_root "ip route add 10.42.0.0/24 dev $IF table $1"
    adb_root "ip route add default via 10.42.0.1 table $1"
}

setup_device_net
setup_host_net

# android maintains seperate routing tables for the devices
# -> set wlan table to route over $IF
fix_routes "$WLANIF"