feat: add ssh-image/ — key-only Dropbear SSH injection for Spike 2 SD images
enable-ssh.sh turns a factory raw SD image (King Kong LE 0.97) into an SSH-enabled one: injects the static dropbear/dropbearkey/sftp-server binaries, the SysV init script (/etc/init.d/sshd), the S30sshd boot symlink and the caller-supplied public key into the ext3 rootfs partition with debugfs (no mounting). The input image is never modified, the output path must be explicit and distinct, and every byte outside p2 is verified identical afterwards. The public key is an explicit -k argument — nothing is baked in and private keys are rejected. --dry-run supported; --force for non-standard p2 geometry. bin/ is byte-identical to the deployed king_kong_le-0_97_0.ssh image. validate-image.sh functionally proves a result (boots the image's own init script under qemu, real ssh pubkey login, password auth refused, sftp round-trip); build-binaries.sh rebuilds bin/ in Docker. Co-Authored-By: Claude Code <noreply@anthropic.com>
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Claude Code
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#!/bin/sh
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# validate-image.sh — functional test of an image produced by enable-ssh.sh.
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#
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# Extracts the output image's rootfs (p2) into a scratch tree (debugfs
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# rdump — no loop device needed) inside a privileged Docker container,
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# starts dropbear via the image's OWN /etc/init.d/sshd (which generates
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# host keys into /data/dropbear exactly as on first boot), then:
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# 1. checks the deployed authorized_keys equals the -k public key you gave
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# enable-ssh.sh (static check, outside the container)
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# 2. ssh-login as root with a throwaway ed25519 key generated INSIDE the
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# container (no private key of yours is ever read or stored)
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# 3. confirms password auth is refused
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# 4. runs sftp put/get to prove the sftp-server wiring
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#
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# The image file itself is only read; all test mutations happen on a scratch
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# copy of p2 inside the container.
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#
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# Usage: validate-image.sh -i OUTPUT_IMAGE -k PUBLIC_KEY [--image docker-image]
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#
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# Requires: docker (linux containers), a volume with ~1 GiB free for the p2
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# scratch copy. Takes a few minutes (container setup + key generation).
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set -eu
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SCRIPT_DIR=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
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INPUT= KEYFILE= DOCKER_IMAGE="debian:12"
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while [ $# -gt 0 ]; do
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case "$1" in
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-i) INPUT=$2; shift 2 ;;
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-k) KEYFILE=$2; shift 2 ;;
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--image) DOCKER_IMAGE=$2; shift 2 ;;
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-h|--help) sed -n '2,30p' "$0" | sed 's/^# \{0,1\}//'; exit 0 ;;
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*) echo "error: unknown argument: $1" >&2; exit 2 ;;
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esac
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done
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err() { echo "error: $*" >&2; exit 1; }
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say() { echo "[validate] $*"; }
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[ -n "$INPUT" ] && [ -n "$KEYFILE" ] || { err "usage: validate-image.sh -i OUTPUT_IMAGE -k PUBLIC_KEY"; }
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[ -f "$INPUT" ] || err "image not found: $INPUT"
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[ -f "$KEYFILE" ] || err "public key not found: $KEYFILE"
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command -v docker >/dev/null 2>&1 || err "docker not found"
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docker info >/dev/null 2>&1 || err "docker daemon not reachable"
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# --- parse the MBR (read-only) for p2 ----------------------------------------
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P2_INFO=$(python3 - "$INPUT" <<'PYEOF'
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import struct, sys
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with open(sys.argv[1], "rb") as f:
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mbr = f.read(512)
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assert mbr[510:512] == b"\x55\xaa", "no MBR boot signature"
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for i in range(4):
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e = mbr[446 + 16*i : 446 + 16*(i+1)]
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if e and e != b"\x00" * 16 and e[4] == 0x83:
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lba, size = struct.unpack("<II", e[8:16])
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if size:
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print(lba, size)
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break
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else:
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sys.exit("no Linux (0x83) partition")
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PYEOF
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) || err "MBR parse failed"
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P2_SECTORS=$(echo "$P2_INFO" | cut -d' ' -f1)
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P2_SIZE_SECTORS=$(echo "$P2_INFO" | cut -d' ' -f2)
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P2_OFFSET=$((P2_SECTORS * 512))
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P2_SIZE=$((P2_SIZE_SECTORS * 512))
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WORK=$(mktemp -d "${TMPDIR:-/tmp}/ssh-validate.XXXXXX")
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trap 'rm -rf "$WORK"' EXIT
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# keep the scratch under $HOME on macOS: Docker Desktop bind-mounts under /tmp
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# are unreliable (see pinball-assets/README.md "Gotchas learned"). If $WORK is
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# under /tmp, copy it to $HOME.
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case "$WORK" in
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/tmp/*|/var/folders/*) WORK_HOME="$HOME/.ssh-validate.$$"; mkdir -p "$WORK_HOME"; trap 'rm -rf "$WORK" "$WORK_HOME"' EXIT; WORK="$WORK_HOME" ;;
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esac
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say "extracting p2 from $INPUT (read-only) -> $WORK/p2.img"
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dd if="$INPUT" of="$WORK/p2.img" bs=512 skip="$P2_SECTORS" count="$P2_SIZE_SECTORS" 2>/dev/null
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[ "$(wc -c < "$WORK/p2.img" | tr -d '[:space:]')" = "$P2_SIZE" ] || err "p2 extraction size mismatch"
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# --- static check: deployed authorized_keys must equal the -k input -----------
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say "static check: authorized_keys in the image vs -k file"
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debugfs -R "dump /home/root/.ssh/authorized_keys $WORK/deployed-ak" "$WORK/p2.img" 2>/dev/null \
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|| err "image has no /home/root/.ssh/authorized_keys (was it built with enable-ssh.sh?)"
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# normalise: ignore trailing-newline differences
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tr -d '\n' < "$WORK/deployed-ak" > "$WORK/deployed-ak.n"
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tr -d '\n' < "$KEYFILE" > "$WORK/keyfile.n"
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if ! cmp -s "$WORK/deployed-ak.n" "$WORK/keyfile.n"; then
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err "authorized_keys in the image does not match -k ($KEYFILE)"
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fi
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say " authorized_keys matches"
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# --- container test ------------------------------------------------------------
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say "running container test ($DOCKER_IMAGE, ~a few minutes) ..."
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cat > "$WORK/container-test.sh" <<'TEST'
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#!/bin/sh
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set -e
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apt-get update -qq >/dev/null
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apt-get install -y -qq openssh-client qemu-user-static e2fsprogs >/dev/null 2>&1
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# extract the rootfs to a scratch tree with debugfs (no loop device needed —
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# Docker Desktop for Mac does not provide one; rdump preserves symlinks and modes)
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mkdir -p /mnt2
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debugfs -R 'rdump / /mnt2' /work/p2.img 2>/dev/null
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echo "--- rootfs extracted (scratch copy); sanity ---"
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ls -la /mnt2/bin/sh /mnt2/etc/init.d/sshd /mnt2/usr/local/bin/dropbear
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# chrooted ARM binaries need an explicit qemu prefix (no binfmt in the container)
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cp /usr/bin/qemu-arm-static /mnt2/usr/bin/
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mount --bind /dev /mnt2/dev
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mount -t proc proc /mnt2/proc
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# start dropbear exactly the way the machine will, via the image's own init
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# script (first-boot path: generates host keys into /data/dropbear, then runs
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# the daemon on port 22)
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echo "--- /etc/init.d/sshd start ---"
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timeout 300 chroot /mnt2 /usr/bin/qemu-arm-static /bin/sh /etc/init.d/sshd start
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sleep 3
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ls -la /mnt2/data/dropbear/
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echo "--- pubkey login test (throwaway key, user root) ---"
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ssh-keygen -t ed25519 -N '' -f /tmp/vkey -q
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mkdir -p /mnt2/home/root/.ssh
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cp /tmp/vkey.pub /mnt2/home/root/.ssh/authorized_keys
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chmod 700 /mnt2/home/root/.ssh; chmod 600 /mnt2/home/root/.ssh/authorized_keys
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if ! timeout 90 ssh -i /tmp/vkey -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null \
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-p 22 root@127.0.0.1 'echo LOGIN-OK as $(whoami) on $(hostname); uname -m' > /tmp/sshout 2>&1; then
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echo "FAIL: pubkey login did not succeed"; cat /tmp/sshout; exit 1
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fi
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grep -v Warning /tmp/sshout
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echo "--- password auth must be refused ---"
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if timeout 30 ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null \
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-o PubkeyAuthentication=no -o NumberOfPasswordPrompts=0 \
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-p 22 root@127.0.0.1 'echo SHOULD-NOT-PRINT' 2>/dev/null; then
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echo "FAIL: password auth was accepted"; exit 1
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fi
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echo " (refused, as expected)"
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echo "--- sftp put/get test ---"
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echo hello-spike2 > /work/sftp-test.txt
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if ! timeout 60 sftp -P 22 -i /tmp/vkey -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null \
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root@127.0.0.1 <<'SFTP' >/dev/null 2>&1
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put /work/sftp-test.txt /tmp/sftp-test.txt
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get /tmp/sftp-test.txt /work/sftp-back.txt
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SFTP
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then
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echo "FAIL: sftp session failed"
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exit 1
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fi
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cmp /work/sftp-test.txt /work/sftp-back.txt
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echo " sftp round-trip OK"
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echo "=== VALIDATE-ALL-OK ==="
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exit 0
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TEST
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chmod +x "$WORK/container-test.sh"
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if ! docker run --rm --privileged \
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-v "$WORK:/work:rw" \
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"$DOCKER_IMAGE" \
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/bin/sh /work/container-test.sh; then
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err "container test failed"
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fi
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say "PASS: key-only sshd boots from the image's own init script, pubkey login works, password auth refused, sftp works."
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say "(scratch p2 and container artifacts deleted; your image file was only read)"
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