fix(setup): add paranoid checksum mode

README.md

@@ -460,6 +460,8 @@ curl -sSL https://github.com/deeplethe/forkd/releases/download/v0.5.2/forkd-v0.5
 
 # 2. Host bring-up:
 sudo bash scripts/setup-host.sh           # KVM + tap device, one-time
+# Or, checksum-verified host bring-up:
+# sudo bash scripts/setup-host.sh --paranoid
 sudo bash scripts/netns-setup.sh 3        # per-child network namespaces
 
 # 3. Sanity-check:

scripts/setup-host.sh

@@ -7,6 +7,136 @@ set -euo pipefail
 say() { printf "\033[1;34m==>\033[0m %s\n" "$*"; }
 die() { printf "\033[1;31merror:\033[0m %s\n" "$*" >&2; exit 1; }
 
+usage() {
+    cat <<'EOF'
+Usage: scripts/setup-host.sh [--paranoid]
+
+Options:
+  --paranoid  Download pinned rustup-init and Firecracker archives, verify
+              their sha256 sums, then install them. Default behavior is unchanged.
+  -h, --help  Show this help text.
+EOF
+}
+
+PARANOID=0
+for arg in "$@"; do
+    case "$arg" in
+        --paranoid) PARANOID=1 ;;
+        -h|--help) usage; exit 0 ;;
+        *) usage >&2; die "unknown argument: $arg" ;;
+    esac
+done
+
+RUSTUP_VERSION="1.29.0"
+RUSTUP_X86_64_SHA256="4acc9acc76d5079515b46346a485974457b5a79893cfb01112423c89aeb5aa10"
+RUSTUP_AARCH64_SHA256="9732d6c5e2a098d3521fca8145d826ae0aaa067ef2385ead08e6feac88fa5792"
+
+FC_VERSION="v1.10.1"
+FC_X86_64_SHA256="36112969952b0e34fadcfca769d48a55dc22cbba99af17e02bd0e24fc35adc77"
+FC_AARCH64_SHA256="9e3641071de140979afaac0c52fdc107baeba398bdb5709c12f77ee469207fcd"
+
+TEMP_DIRS=()
+cleanup_temp_dirs() {
+    if [ "${#TEMP_DIRS[@]}" -eq 0 ]; then
+        return
+    fi
+    rm -rf "${TEMP_DIRS[@]}"
+}
+trap cleanup_temp_dirs EXIT
+
+make_temp_dir() {
+    local -n outvar="$1"
+    outvar="$(mktemp -d)"
+    TEMP_DIRS+=("$outvar")
+}
+
+host_arch() {
+    case "$(uname -m)" in
+        x86_64) printf "x86_64\n" ;;
+        aarch64|arm64) printf "aarch64\n" ;;
+        *) die "unsupported architecture for setup-host.sh: $(uname -m)" ;;
+    esac
+}
+
+rustup_triple() {
+    case "$1" in
+        x86_64) printf "x86_64-unknown-linux-gnu\n" ;;
+        aarch64) printf "aarch64-unknown-linux-gnu\n" ;;
+        *) die "unsupported architecture for rustup-init: $1" ;;
+    esac
+}
+
+rustup_sha256() {
+    case "$1" in
+        x86_64-unknown-linux-gnu) printf "%s\n" "$RUSTUP_X86_64_SHA256" ;;
+        aarch64-unknown-linux-gnu) printf "%s\n" "$RUSTUP_AARCH64_SHA256" ;;
+        *) die "missing rustup-init sha256 for $1" ;;
+    esac
+}
+
+firecracker_sha256() {
+    case "$1" in
+        x86_64) printf "%s\n" "$FC_X86_64_SHA256" ;;
+        aarch64) printf "%s\n" "$FC_AARCH64_SHA256" ;;
+        *) die "missing Firecracker sha256 for $1" ;;
+    esac
+}
+
+download_and_verify() {
+    local url="$1"
+    local dest="$2"
+    local expected="$3"
+    local label="$4"
+    local actual
+
+    curl -fsSL "$url" -o "$dest"
+    actual="$(sha256sum "$dest" | awk '{print $1}')"
+    if [ "$actual" != "$expected" ]; then
+        die "$label sha256 mismatch: expected $expected, got $actual"
+    fi
+}
+
+install_rustup_paranoid() {
+    local arch triple expected tmp rustup_init
+    arch="$(host_arch)"
+    triple="$(rustup_triple "$arch")"
+    expected="$(rustup_sha256 "$triple")"
+    make_temp_dir tmp
+    rustup_init="$tmp/rustup-init"
+
+    say "Downloading rustup-init $RUSTUP_VERSION ($triple) with sha256 verification..."
+    download_and_verify \
+        "https://static.rust-lang.org/rustup/archive/${RUSTUP_VERSION}/${triple}/rustup-init" \
+        "$rustup_init" \
+        "$expected" \
+        "rustup-init ${RUSTUP_VERSION} ${triple}"
+    chmod 0755 "$rustup_init"
+    "$rustup_init" -y
+}
+
+install_firecracker_from_archive() {
+    local arch="$1"
+    local tmp archive
+    make_temp_dir tmp
+    archive="$tmp/firecracker-${FC_VERSION}-${arch}.tgz"
+
+    if [ "$PARANOID" -eq 1 ]; then
+        say "Downloading Firecracker $FC_VERSION ($arch) with sha256 verification..."
+        download_and_verify \
+            "https://github.com/firecracker-microvm/firecracker/releases/download/${FC_VERSION}/firecracker-${FC_VERSION}-${arch}.tgz" \
+            "$archive" \
+            "$(firecracker_sha256 "$arch")" \
+            "Firecracker ${FC_VERSION} ${arch}"
+        tar -xzf "$archive" -C "$tmp"
+    else
+        curl -fsSL "https://github.com/firecracker-microvm/firecracker/releases/download/${FC_VERSION}/firecracker-${FC_VERSION}-${arch}.tgz" \
+            | tar -xz -C "$tmp"
+    fi
+
+    install -m 0755 "$tmp/release-${FC_VERSION}-${arch}/firecracker-${FC_VERSION}-${arch}" "$HOME/.local/bin/firecracker"
+    install -m 0755 "$tmp/release-${FC_VERSION}-${arch}/jailer-${FC_VERSION}-${arch}" "$HOME/.local/bin/jailer"
+}
+
 say "Checking hardware virtualization support..."
 if [ "$(grep -Ec '(vmx|svm)' /proc/cpuinfo)" -eq 0 ]; then
     die "CPU does not advertise VT-x / AMD-V. forkd needs KVM."
@@ -40,31 +170,23 @@ say "Installing Rust (if missing)..."
 # rustup binary version that lands here does NOT determine what compiler
 # forkd actually builds with — `rust-toolchain.toml` at the repo root
 # pins the channel (currently `stable`), and rustup fetches that
-# toolchain on first `cargo build`. So a supply-chain compromise of
-# `sh.rustup.rs` would still be bounded by what rustup-init does
-# locally; the project itself remains pinned.
-# See #236 for the security discussion. Future work: a `--paranoid` mode
-# that downloads the rustup-init binary and verifies sha256 before
-# executing. Not done now because the sha256 needs to be refreshed on
-# every rustup-init release, which trades supply-chain hygiene for
-# maintenance staleness.
+# toolchain on first `cargo build`. The default remains curl-pipe-sh;
+# pass --paranoid to verify a pinned rustup-init binary before running it.
 if ! command -v cargo >/dev/null; then
-    curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+    if [ "$PARANOID" -eq 1 ]; then
+        install_rustup_paranoid
+    else
+        curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+    fi
     # shellcheck disable=SC1091
     source "$HOME/.cargo/env"
 fi
 
-FC_VERSION="v1.10.1"
-ARCH="$(uname -m)"
+ARCH="$(host_arch)"
 say "Installing Firecracker $FC_VERSION ($ARCH)..."
 mkdir -p "$HOME/.local/bin"
 if [ ! -x "$HOME/.local/bin/firecracker" ]; then
-    TMP="$(mktemp -d)"
-    curl -fsSL "https://github.com/firecracker-microvm/firecracker/releases/download/${FC_VERSION}/firecracker-${FC_VERSION}-${ARCH}.tgz" \
-        | tar -xz -C "$TMP"
-    install -m 0755 "$TMP/release-${FC_VERSION}-${ARCH}/firecracker-${FC_VERSION}-${ARCH}" "$HOME/.local/bin/firecracker"
-    install -m 0755 "$TMP/release-${FC_VERSION}-${ARCH}/jailer-${FC_VERSION}-${ARCH}" "$HOME/.local/bin/jailer"
-    rm -rf "$TMP"
+    install_firecracker_from_archive "$ARCH"
 fi
 
 case ":$PATH:" in