ForwardingMachine + Cert() overhaul (#4784)

* New: ForwardingMachine

* Document forwarding machines, split Advanced Usage

* Improve naming and forwarding machine

* Add debug_strfixedlenfield

* Cleanup Cert/Key handling a LOT

* CI fixes

* Fix TLS 1.3 exchange

* Fix doc

* Make pem format string instead of bytes

Author: gpotter2

doc/scapy/_static/vethrelay.sh

@@ -0,0 +1,74 @@
+#!/bin/bash
+
+# Setup iptables for IP relay by creating an interface configured
+# to be the destination of TPROXY rules.
+
+if [ "$EUID" -ne 0 ]
+  then echo "Please run as root"
+  exit
+fi
+
+if [ "$1" != "setup" ] && [ "$1" != "unsetup" ]; then
+    echo -e "Usage: ./vethrelay <setup/unsetup>\n"
+    exit 1
+fi
+
+IFACE="vethrelay"
+IP="2.2.2.2"
+
+# Linux doc about TPROXY and example regarding this:
+# https://www.kernel.org/doc/Documentation/networking/tproxy.txt
+# https://powerdns.org/tproxydoc/tproxy.md.html
+
+function checkSetup() {
+    iptables -t mangle -n --list "DIVERT" >/dev/null 2>&1
+    return $?
+}
+
+if [ "$1" == "setup" ]; then
+    # Add "DIVERT" chain if it doesn't exist
+    checkSetup
+    if [ $? -eq 0 ]; then
+        echo "vethrelay already setup !"
+        exit 1
+    fi
+    # Create an interface tcpreplay dedicated to relay
+    ip link add dev $IFACE type dummy
+    sysctl net.ipv6.conf.$IFACE.disable_ipv6=1 >/dev/null
+    ip link set dev $IFACE up
+    ip addr add dev $IFACE $IP/32
+    # Create mangle "DIVERT" chain as an optimisation. -m socket matches
+    # packets from already established sockets. Those are marked as 1 then
+    # accepted directly.
+    iptables -t mangle -N DIVERT
+    iptables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT
+    iptables -t mangle -A DIVERT -j MARK --set-mark 1
+    iptables -t mangle -A DIVERT -j ACCEPT
+    # Packets marked with 1 are routed through table 100 instead of the
+    # default routing table
+    ip rule add fwmark 1 lookup 100
+    # In routing table 100, all IPs are local to 'vethrelay'
+    ip route add local 0.0.0.0/0 dev $IFACE table 100
+    echo -e "\x1b[32mInterface $IFACE is now setup with IPv4: $IP !\x1b[0m\n"
+    echo -e "Add listening rules as follow:\n"
+    echo "# TPROXY incoming TCP packets on port 80 to $IFACE on port 8080"
+    echo "iptables -t mangle -A PREROUTING -p tcp --dport 80 -j TPROXY --tproxy-mark 0x1/0x1 --on-port 8080 --on-ip $IP"
+    echo
+    echo "# Listen on wlp4s0 for incoming packets on port 80 (on the interface where it really comes from)"
+    echo "iptables -A INPUT -i wlp4s0 -p tcp --dport 80 -j ACCEPT"
+elif [ "$1" == "unsetup" ]; then
+    checkSetup
+    if [ $? -ne 0 ]; then
+        echo "vethrelay not setup !"
+        exit 1
+    fi
+    # Remove all setup rules
+    sudo ip rule del fwmark 1 lookup 100
+    sudo ip route del local 0.0.0.0/0 dev $IFACE table 100
+    sudo iptables -t mangle -D DIVERT -j ACCEPT
+    sudo iptables -t mangle -D DIVERT -j MARK --set-mark 1
+    sudo iptables -t mangle -D PREROUTING -p tcp -m socket -j DIVERT
+    sudo iptables -t mangle -X DIVERT
+    sudo ip link del dev $IFACE
+    echo -e "\x1b[32mInterface $IFACE unsetup !\x1b[0m"
+fi