Harden lock authentication command lookup

Keep the target user's local bin on user-scoped upgrade paths while giving privileged lock and firewall helpers only root-owned search directories. Pin the lock helper's root PATH and fprintd-list executable, with regression coverage for each defense independently.

Reported-by: Rooke Poole <rookpool97@gmail.com>

bin/omarchy-apply-lock

@@ -6,6 +6,12 @@
 
 set -e
 
+# Install and upgrade callers can start this helper as root. Ignore their PATH
+# so optional commands never fall through to a user-writable directory.
+if (( EUID == 0 )); then
+  export PATH=/usr/share/omarchy/bin:/usr/local/bin:/usr/bin:/bin
+fi
+
 target_user=${OMARCHY_INSTALL_USER:-${SUDO_USER:-}}
 if [[ -z $target_user && -n ${PKEXEC_UID:-} ]]; then
   target_user=$(getent passwd "$PKEXEC_UID" | cut -d: -f1)
@@ -34,7 +40,8 @@ auth       required                    pam_faillock.so authsucc
 account    include                     system-local-login
 EOF
 
-if omarchy-cmd-present fprintd-list && fprintd-list "$target_user" 2>/dev/null | grep -qi finger; then
+if [[ -x /usr/bin/fprintd-list ]] &&
+  /usr/bin/fprintd-list "$target_user" 2>/dev/null | grep -qi finger; then
   echo "Configuring lock screen fingerprint authentication..."
   as_root tee /etc/pam.d/omarchy-lock-fingerprint >/dev/null <<'EOF'
 #%PAM-1.0

bin/omarchy-upgrade-to-quattro

@@ -175,7 +175,10 @@ target_home=$(getent passwd "$target_user" | cut -d: -f6)
 [[ -n $target_home && -d $target_home ]] || fail "Home directory for '$target_user' was not found."
 target_uid=$(id -u "$target_user")
 target_runtime_dir="/run/user/$target_uid"
-package_path="/usr/share/omarchy/bin:/usr/local/bin:/usr/bin:/bin:$target_home/.local/bin"
+# User-local commands are needed only after dropping to the target user. Never
+# expose their search path to commands run through as_root.
+root_path=/usr/share/omarchy/bin:/usr/local/bin:/usr/bin:/bin
+package_path="$root_path:$target_home/.local/bin"
 
 as_root() {
   if (( EUID == 0 )); then
@@ -661,7 +664,7 @@ configure_lock_authentication() {
   as_root env \
     OMARCHY_INSTALL_USER="$target_user" \
     OMARCHY_PATH=/usr/share/omarchy \
-    PATH="$package_path" \
+    PATH="$root_path" \
     "$apply_lock"
 }
 
@@ -1287,7 +1290,7 @@ apply_firewall_defaults() {
   fi
 
   log "Applying Omarchy firewall defaults"
-  as_root env OMARCHY_PATH=/usr/share/omarchy PATH="$package_path" \
+  as_root env OMARCHY_PATH=/usr/share/omarchy PATH="$root_path" \
     bash -euo pipefail "$firewall_script" ||
     warn "Could not apply firewall defaults; run 'sudo bash $firewall_script' after reboot."
 }

test/shell.d/apply-lock-test.sh

@@ -0,0 +1,206 @@
+#!/bin/bash
+
+set -euo pipefail
+
+source "$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)/base-test.sh"
+
+apply_lock="$ROOT/bin/omarchy-apply-lock"
+
+root_path_guard=$(awk '
+  /^if \(\( EUID == 0 \)\); then$/ { inside = 1 }
+  inside { print }
+  inside && /^fi$/ { exit }
+' "$apply_lock")
+grep -Fx '  export PATH=/usr/share/omarchy/bin:/usr/local/bin:/usr/bin:/bin' <<<"$root_path_guard" >/dev/null ||
+  fail "the root lock helper replaces its inherited command path"
+if grep -E '(\.local/bin|target_user|target_home)' <<<"$root_path_guard" >/dev/null; then
+  fail "the root lock helper does not retain a user-controlled command directory"
+fi
+pass "the root lock helper uses only trusted command directories"
+
+grep -F '[[ -x /usr/bin/fprintd-list ]]' "$apply_lock" >/dev/null ||
+  fail "the lock helper checks the trusted fprintd-list executable"
+grep -F '/usr/bin/fprintd-list "$target_user"' "$apply_lock" >/dev/null ||
+  fail "the lock helper invokes fprintd-list by its trusted absolute path"
+if grep -F 'omarchy-cmd-present fprintd-list' "$apply_lock" >/dev/null ||
+  grep -E '(^|[[:space:];&|])fprintd-list([[:space:]]|$)' "$apply_lock" >/dev/null ||
+  grep -E 'command[[:space:]]+-v[[:space:]]+fprintd-list' "$apply_lock" >/dev/null; then
+  fail "the lock helper does not resolve fprintd-list through PATH"
+fi
+pass "the lock helper pins fprintd-list to its packaged system path"
+
+# Exercise the helper as real root when the suite already has it, or as root in
+# an unprivileged user namespace otherwise. A hardened kernel can disable user
+# namespaces, so preserve the static coverage above and skip only this probe.
+root_runner=()
+root_runtime_available=1
+if (( EUID != 0 )); then
+  if command -v unshare >/dev/null && unshare --user --map-root-user true 2>/dev/null; then
+    root_runner=(unshare --user --map-root-user)
+  else
+    root_runtime_available=0
+  fi
+fi
+
+if (( ! root_runtime_available )); then
+  pass "no unprivileged user namespace; skipping the root lock-helper lookup matrix"
+  exit 0
+fi
+
+# Retarget the two PAM files, the trusted fprintd-list binary, and the final
+# shell status query in copies under this scratch directory. The production
+# files and service stay untouched even when this suite itself runs as root.
+test_tmp=$(mktemp -d)
+trap 'rm -rf "$test_tmp"' EXIT
+
+poison_bin="$test_tmp/poison-bin"
+trusted_root_bin="$test_tmp/trusted-root-bin"
+trusted_fprintd="$test_tmp/trusted-fprintd-list"
+password_pam="$test_tmp/omarchy-lock-password"
+fingerprint_pam="$test_tmp/omarchy-lock-fingerprint"
+attack_marker="$test_tmp/user-fprintd-list-ran"
+trusted_uid="$test_tmp/trusted-fprintd-list.uid"
+trusted_args="$test_tmp/trusted-fprintd-list.args"
+attack_args="$test_tmp/user-fprintd-list.args"
+patched_helper="$test_tmp/omarchy-apply-lock-patched"
+absolute_only_helper="$test_tmp/omarchy-apply-lock-absolute-only"
+root_path_only_helper="$test_tmp/omarchy-apply-lock-root-path-only"
+unprotected_helper="$test_tmp/omarchy-apply-lock-unprotected"
+target_user=omarchy-regression-user
+mkdir -p "$poison_bin" "$trusted_root_bin"
+
+# The runtime copy pins to this isolated root path. It contains every bare
+# command the exercised helper needs, but deliberately no fprintd-list.
+for helper in grep rm tee; do
+  ln -s "/usr/bin/$helper" "$trusted_root_bin/$helper"
+done
+
+export TEST_ATTACK_ARGS="$attack_args"
+export TEST_ATTACK_MARKER="$attack_marker"
+export TEST_TRUSTED_ARGS="$trusted_args"
+export TEST_TRUSTED_UID="$trusted_uid"
+
+cat >"$trusted_fprintd" <<'EOF'
+#!/bin/bash
+
+printf '%s\n' "$EUID" >"$TEST_TRUSTED_UID"
+printf '%s\n' "$*" >"$TEST_TRUSTED_ARGS"
+echo "Fingerprints are enrolled"
+EOF
+
+cat >"$poison_bin/fprintd-list" <<'EOF'
+#!/bin/bash
+
+printf '%s\n' "$EUID" >"$TEST_ATTACK_MARKER"
+printf '%s\n' "$*" >"$TEST_ATTACK_ARGS"
+echo "Fingerprints are enrolled"
+EOF
+
+chmod +x "$trusted_fprintd" "$poison_bin/fprintd-list"
+
+prepare_helper() {
+  local destination="$1" keep_root_path="$2" use_absolute_fprintd="$3"
+
+  awk \
+    -v password_pam="$password_pam" \
+    -v fingerprint_pam="$fingerprint_pam" \
+    -v trusted_root_bin="$trusted_root_bin" \
+    -v trusted_fprintd="$trusted_fprintd" \
+    -v keep_root_path="$keep_root_path" \
+    -v use_absolute_fprintd="$use_absolute_fprintd" '
+    {
+      line = $0
+      gsub("/etc/pam\\.d/omarchy-lock-password", "\"" password_pam "\"", line)
+      gsub("/etc/pam\\.d/omarchy-lock-fingerprint", "\"" fingerprint_pam "\"", line)
+
+      if (line == "if (( EUID == 0 )); then" && keep_root_path == 0) {
+        print "if (( 0 )); then"
+        next
+      }
+      if (line == "  export PATH=/usr/share/omarchy/bin:/usr/local/bin:/usr/bin:/bin") {
+        print "  export PATH=\"" trusted_root_bin "\""
+        next
+      }
+      if (line == "if [[ -x /usr/bin/fprintd-list ]] &&") {
+        if (use_absolute_fprintd == 1) {
+          print "if [[ -x \"" trusted_fprintd "\" ]] &&"
+        } else {
+          print "if command -v fprintd-list >/dev/null 2>&1 &&"
+        }
+        next
+      }
+      if (line == "  /usr/bin/fprintd-list \"$target_user\" 2>/dev/null | grep -qi finger; then") {
+        if (use_absolute_fprintd == 1) {
+          print "  \"" trusted_fprintd "\" \"$target_user\" 2>/dev/null | grep -qi finger; then"
+        } else {
+          print "  fprintd-list \"$target_user\" 2>/dev/null | grep -qi finger; then"
+        }
+        next
+      }
+      if (line == "if omarchy-shell lock status >/dev/null 2>&1; then") {
+        print "if false; then"
+        next
+      }
+
+      print line
+    }
+  ' "$apply_lock" >"$destination"
+  chmod +x "$destination"
+}
+
+prepare_helper "$patched_helper" 1 1
+prepare_helper "$absolute_only_helper" 0 1
+prepare_helper "$root_path_only_helper" 1 0
+prepare_helper "$unprotected_helper" 0 0
+
+for helper in "$patched_helper" "$absolute_only_helper" "$root_path_only_helper" "$unprotected_helper"; do
+  if grep -F '/etc/pam.d/' "$helper" >/dev/null ||
+    grep -F '/usr/bin/fprintd-list' "$helper" >/dev/null ||
+    grep -F 'omarchy-shell lock status' "$helper" >/dev/null; then
+    fail "the isolated root fixture redirects every live-system lock-helper target"
+  fi
+done
+
+reset_runtime_files() {
+  rm -f "$password_pam" "$fingerprint_pam" "$trusted_uid" "$trusted_args" "$attack_marker" "$attack_args"
+}
+
+run_as_root() {
+  local helper="$1" description="$2" output
+
+  if ! output=$(PATH="$poison_bin:/usr/bin:/bin" OMARCHY_INSTALL_USER="$target_user" \
+    "${root_runner[@]}" /bin/bash "$helper" 2>&1); then
+    fail "$description" "$output"
+  fi
+}
+
+reset_runtime_files
+run_as_root "$patched_helper" "the fully hardened lock helper runs in an isolated root context"
+[[ ! -e $attack_marker ]] || fail "the hardened root lock helper executes the user-planted fprintd-list"
+grep -Fx '0' "$trusted_uid" >/dev/null || fail "the trusted fprintd-list probe runs with EUID 0"
+grep -Fx "$target_user" "$trusted_args" >/dev/null || fail "the trusted fprintd-list probe receives the target user"
+[[ -s $password_pam && -s $fingerprint_pam ]] ||
+  fail "the isolated root lock-helper run writes both scratch PAM fixtures"
+pass "the hardened root lock helper uses the trusted fingerprint probe"
+
+reset_runtime_files
+run_as_root "$absolute_only_helper" "the absolute-path-only lock helper runs in an isolated root context"
+[[ ! -e $attack_marker ]] || fail "an absolute fprintd-list path permits the user-planted command"
+grep -Fx '0' "$trusted_uid" >/dev/null || fail "the absolute-path defense runs the trusted probe as root"
+pass "the absolute fprintd-list path independently blocks the user-planted command"
+
+reset_runtime_files
+run_as_root "$root_path_only_helper" "the root-PATH-only lock helper runs in an isolated root context"
+[[ ! -e $attack_marker ]] || fail "the trusted root path permits the user-planted fprintd-list"
+pass "the trusted root path independently blocks the user-planted command"
+
+# Mutation control: removing both protections must execute the planted command
+# as UID 0, proving the matrix detects the original privilege-boundary failure.
+reset_runtime_files
+run_as_root "$unprotected_helper" "the unprotected mutation runs in an isolated root context"
+grep -Fx '0' "$attack_marker" >/dev/null ||
+  fail "the root lock-helper fixture detects a PATH-resolved fprintd-list regression"
+grep -Fx "$target_user" "$attack_args" >/dev/null ||
+  fail "the planted fprintd-list receives the target user"
+[[ -s $fingerprint_pam ]] || fail "the planted fprintd-list controls the fingerprint PAM branch"
+pass "the root lock-helper matrix rejects the vulnerable PATH lookup"

test/shell.d/upgrade-to-quattro-test.sh

@@ -6,6 +6,10 @@ source "$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)/base-test.sh"
 
 upgrade_to_quattro="$ROOT/bin/omarchy-upgrade-to-quattro"
 
+function_body() {
+  awk -v name="$1" '$0 == name "() {" { inside = 1; next } inside && $0 == "}" { exit } inside' "$upgrade_to_quattro"
+}
+
 snapshot_line=$(grep -n '^create_pre_upgrade_snapshot$' "$upgrade_to_quattro" | cut -d: -f1)
 pacman_line=$(grep -n '^configure_pacman_channel$' "$upgrade_to_quattro" | cut -d: -f1)
 [[ -n $snapshot_line && -n $pacman_line ]] || fail "upgrade snapshot and first mutation calls exist"
@@ -73,6 +77,44 @@ grep -F 'OMARCHY_INSTALL_USER="$target_user"' "$upgrade_to_quattro" >/dev/null
 grep -F '"$apply_lock"' "$upgrade_to_quattro" >/dev/null
 pass "Omarchy 4 upgrade configures lock screen authentication for the target user"
 
+root_path_count=$(awk '/^root_path=/{ count++ } END { print count + 0 }' "$upgrade_to_quattro")
+(( root_path_count == 1 )) || fail "Omarchy 4 upgrade defines exactly one root command path"
+grep -Fx 'root_path=/usr/share/omarchy/bin:/usr/local/bin:/usr/bin:/bin' "$upgrade_to_quattro" >/dev/null ||
+  fail "Omarchy 4 upgrade limits root command lookup to trusted system directories"
+if grep -E '^root_path=.*(target_home|\.local/bin)' "$upgrade_to_quattro" >/dev/null; then
+  fail "Omarchy 4 upgrade does not put the target user's bin directory on the root command path"
+fi
+grep -Fx 'package_path="$root_path:$target_home/.local/bin"' "$upgrade_to_quattro" >/dev/null ||
+  fail "Omarchy 4 upgrade retains the target user's bin directory for user commands"
+
+lock_authentication_body=$(function_body configure_lock_authentication)
+lock_path_assignment_count=$(awk '{ count += gsub(/(^|[[:space:]])PATH=/, "") } END { print count + 0 }' <<<"$lock_authentication_body")
+(( lock_path_assignment_count == 1 )) ||
+  fail "Omarchy 4 upgrade gives the privileged lock helper exactly one command path"
+grep -Fx '    PATH="$root_path" \' <<<"$lock_authentication_body" >/dev/null ||
+  fail "Omarchy 4 upgrade gives the privileged lock helper the trusted root path"
+if grep -E '(package_path|target_home|\.local/bin)' <<<"$lock_authentication_body" >/dev/null; then
+  fail "Omarchy 4 upgrade does not give the privileged lock helper the target user's path"
+fi
+
+firewall_body=$(function_body apply_firewall_defaults)
+firewall_path_assignment_count=$(awk '{ count += gsub(/(^|[[:space:]])PATH=/, "") } END { print count + 0 }' <<<"$firewall_body")
+(( firewall_path_assignment_count == 1 )) ||
+  fail "Omarchy 4 upgrade gives the privileged firewall helper exactly one command path"
+grep -Fx '  as_root env OMARCHY_PATH=/usr/share/omarchy PATH="$root_path" \' <<<"$firewall_body" >/dev/null ||
+  fail "Omarchy 4 upgrade gives the privileged firewall helper the trusted root path"
+if grep -E '(package_path|target_home|\.local/bin)' <<<"$firewall_body" >/dev/null; then
+  fail "Omarchy 4 upgrade does not give the privileged firewall helper the target user's path"
+fi
+
+user_omarchy_body=$(function_body run_as_user_omarchy)
+grep -F 'PATH="$package_path"' <<<"$user_omarchy_body" >/dev/null ||
+  fail "Omarchy 4 upgrade retains the package and user path for target-user commands"
+if grep -F 'PATH="$root_path"' <<<"$user_omarchy_body" >/dev/null; then
+  fail "Omarchy 4 upgrade does not narrow target-user commands to the root-only path"
+fi
+pass "Omarchy 4 upgrade separates privileged and target-user command paths"
+
 grep -F 'install/helpers/browser-policy.sh' "$upgrade_to_quattro" >/dev/null ||
   fail "Omarchy 4 upgrade uses the shared browser-policy helper"
 grep -F 'as_root test -f "$browser_policy_helper"' "$upgrade_to_quattro" >/dev/null ||
@@ -100,10 +142,6 @@ pass "Omarchy 4 upgrade retires systemd-networkd for NetworkManager"
 # Booting with both managers enabled leaves them fighting over the Wi-Fi
 # adapter, so enabling NetworkManager and disabling iwd cannot be separated by
 # any step that might abort in between.
-function_body() {
-  awk -v name="$1" '$0 == name "() {" { inside = 1; next } inside && $0 == "}" { exit } inside' "$upgrade_to_quattro"
-}
-
 migrations_body=$(function_body run_post_upgrade_migrations)
 grep -F 'fail "Omarchy migrations did not complete.' <<<"$migrations_body" >/dev/null ||
   fail "Omarchy 4 upgrade fails when a migration cannot complete"