didericis
ce3fad9320
The default TAP-pool base was 100.64.0.0/10 (RFC-6598 CGNAT) — chosen to dodge RFC-1918, but that's exactly the range Tailscale assigns node addresses from, so on a Tailscale host it's the worst pick. Move the default to 10.243.0.0/16, an obscure RFC-1918 block that steers clear of docker/libvirt/k8s/LAN and Tailscale. No default is collision-proof, so add netpool.overlapping_routes(): it parses `ip -json route show table all` and flags any route intersecting the pool range (excluding our own bbfc* TAPs and the default route). The launch preflight warns on overlap; `backend status` reports it. Distribute the NixOS host setup as a flake module instead of a copy-pasted blob: nix/firecracker-netpool.nix computes the taps / nft table from typed options (poolSize, ipBase, ifacePrefix, owner) with a /31-alignment assertion, and flake.nix exposes it as nixosModules.firecracker-netpool. Defaults mirror the backend constants; writeEnvFile emits the matching BOT_BOTTLE_FC_* so the host pool and the launcher can't drift. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01WBMWTEtQdJ4W5UrWuLHCck
163 lines
6.0 KiB
Bash
Executable File
163 lines
6.0 KiB
Bash
Executable File
#!/usr/bin/env bash
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# One-time privileged network setup for the Firecracker backend.
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#
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# Creates a pool of point-to-point TAP devices (owned by the invoking
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# user so the backend can open them without root at launch) and a
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# dedicated nftables table that isolates every VM: a bottle VM can
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# reach only its own sidecar (published on the host-side TAP IP) and
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# nothing else on the host or network.
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#
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# Why a pool + one-time setup: creating a TAP and assigning it an IP
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# needs CAP_NET_ADMIN. Pre-creating user-owned, pre-addressed TAPs
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# means `./cli.py start` never needs root. The nft table is static
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# (keyed on the `bbfc*` interface wildcard), so it covers every slot
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# without per-launch changes.
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#
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# Design notes:
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# * No shared bridge — each slot is an isolated /31 host<->guest link,
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# so there are no bridge name/subnet collisions with docker0,
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# virbr0 (libvirt), cni0 (k8s) or br-* (docker networks).
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# * Own nftables table `bot_bottle_fc` — independent of the iptables
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# filter/nat tables Docker/ufw/firewalld use, so nothing is stomped.
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# * Default IP block is an obscure RFC-1918 /16 (10.243.0.0/16),
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# chosen to dodge the usual occupants (docker 172.17-31, libvirt
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# 192.168.122, k8s 10.42/10.244, home LANs). NOT 100.64.0.0/10 —
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# that's RFC-6598 CGNAT, which Tailscale hands node addresses from.
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#
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# NixOS: imperative rules here do NOT survive nixos-rebuild. Use the
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# declarative module in nix/firecracker-netpool.nix instead (exposed as
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# the flake output nixosModules.firecracker-netpool).
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#
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# Usage:
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# sudo ./scripts/firecracker-netpool.sh up
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# sudo ./scripts/firecracker-netpool.sh down
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# ./scripts/firecracker-netpool.sh status
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#
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# Env overrides (must match the backend's util.py constants):
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# BOT_BOTTLE_FC_POOL_SIZE number of slots (default 8)
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# BOT_BOTTLE_FC_IP_BASE base IPv4 of the /31 pool (default 10.243.0.0)
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# BOT_BOTTLE_FC_IFACE_PREFIX TAP name prefix (default bbfc)
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# BOT_BOTTLE_FC_OWNER owning user (default $SUDO_USER or $USER)
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set -euo pipefail
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POOL_SIZE="${BOT_BOTTLE_FC_POOL_SIZE:-8}"
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IP_BASE="${BOT_BOTTLE_FC_IP_BASE:-10.243.0.0}"
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PREFIX="${BOT_BOTTLE_FC_IFACE_PREFIX:-bbfc}"
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OWNER="${BOT_BOTTLE_FC_OWNER:-${SUDO_USER:-$USER}}"
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TABLE="bot_bottle_fc"
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# Sidecar ports (must match the backend). egress=9099, supervise=9100,
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# git-http=9420. Reached by the VM at its host-side TAP IP.
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SIDECAR_PORTS="9099,9100,9420"
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# --- IP math ---------------------------------------------------------
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# Slot i occupies the /31 {base+2i, base+2i+1}: host = base+2i (the
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# gateway the VM routes through), guest = base+2i+1 (the VM's address).
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_ip_to_int() {
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local IFS=. ; read -r a b c d <<<"$1" ; echo $(( (a<<24) + (b<<16) + (c<<8) + d ))
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}
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_int_to_ip() {
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local n=$1 ; echo "$(( (n>>24)&255 )).$(( (n>>16)&255 )).$(( (n>>8)&255 )).$(( n&255 ))"
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}
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host_ip() { _int_to_ip $(( $(_ip_to_int "$IP_BASE") + 2*$1 )); }
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guest_ip() { _int_to_ip $(( $(_ip_to_int "$IP_BASE") + 2*$1 + 1 )); }
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iface() { echo "${PREFIX}$1"; }
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require_root() {
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if [ "$(id -u)" -ne 0 ]; then
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echo "error: '$1' needs root (run under sudo)" >&2
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exit 1
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fi
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}
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cmd_up() {
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require_root up
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echo "firecracker net pool: $POOL_SIZE slots, base $IP_BASE, owner $OWNER"
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# VM->sidecar traffic is DNAT'd to the sidecar container and
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# forwarded, so forwarding must be enabled (Docker also sets this).
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sysctl -qw net.ipv4.ip_forward=1
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for i in $(seq 0 $((POOL_SIZE-1))); do
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local dev host
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dev="$(iface "$i")" ; host="$(host_ip "$i")"
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if ip link show "$dev" >/dev/null 2>&1; then
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ip link set "$dev" down 2>/dev/null || true
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ip tuntap del dev "$dev" mode tap 2>/dev/null || true
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fi
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ip tuntap add dev "$dev" mode tap user "$OWNER"
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ip addr add "$host/31" dev "$dev"
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ip link set "$dev" up
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echo " $dev host=$host guest=$(guest_ip "$i") owner=$OWNER"
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done
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_install_nft
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echo "nftables table inet $TABLE installed (fail-closed boundary)"
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echo "done."
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}
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_install_nft() {
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# Own table: dropping only matches our bbfc* interfaces, so no other
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# tool's traffic is affected. Priority -10 runs before Docker's
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# filter hooks (priority 0); a drop here is terminal for the packet.
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#
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# forward: VM egress is DNAT'd to the sidecar (established via
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# `ct status dnat`); return traffic via `ct state established`.
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# Anything else from a VM is dropped -> no route to the internet
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# or the rest of the host except through the sidecar proxy.
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# input: a VM never needs host-local delivery (its sidecar is
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# reached via DNAT->forward), so drop all direct input from VMs
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# -> host services bound on 0.0.0.0 are unreachable from the VM.
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nft -f - <<EOF
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table inet $TABLE {
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chain forward {
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type filter hook forward priority -10; policy accept;
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iifname != "${PREFIX}*" return
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ct state established,related accept
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ct status dnat accept
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drop
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}
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chain input {
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type filter hook input priority -10; policy accept;
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iifname != "${PREFIX}*" return
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ct state established,related accept
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drop
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}
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}
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EOF
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}
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cmd_down() {
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require_root down
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nft delete table inet "$TABLE" 2>/dev/null || true
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for i in $(seq 0 $((POOL_SIZE-1))); do
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local dev ; dev="$(iface "$i")"
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if ip link show "$dev" >/dev/null 2>&1; then
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ip link set "$dev" down 2>/dev/null || true
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ip tuntap del dev "$dev" mode tap 2>/dev/null || true
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echo " removed $dev"
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fi
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done
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echo "done."
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}
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cmd_status() {
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echo "table inet $TABLE:"
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nft list table inet "$TABLE" 2>/dev/null || echo " (absent)"
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echo "taps:"
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for i in $(seq 0 $((POOL_SIZE-1))); do
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local dev ; dev="$(iface "$i")"
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if ip -brief addr show "$dev" >/dev/null 2>&1; then
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ip -brief addr show "$dev" | sed 's/^/ /'
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fi
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done
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}
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case "${1:-}" in
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up) cmd_up ;;
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down) cmd_down ;;
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status) cmd_status ;;
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*) echo "usage: $0 {up|down|status}" >&2 ; exit 2 ;;
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esac
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