sudo: add kill-child.sh

ultimately, a non-previlieged child cannot kill previlieged parent.
all the notes and research in shell.js are not useful.

setup/start/sudoers

@@ -71,4 +71,7 @@ yellowtent ALL=(root) NOPASSWD: /home/yellowtent/box/src/scripts/hdparm.sh
 Defaults!/home/yellowtent/box/src/scripts/hdparm.sh env_keep="HOME BOX_ENV"
 yellowtent ALL=(root) NOPASSWD: /home/yellowtent/box/src/scripts/logtail.sh
 
+Defaults!/home/yellowtent/box/src/scripts/kill-child.sh env_keep="HOME BOX_ENV"
+yellowtent ALL=(root) NOPASSWD: /home/yellowtent/box/src/scripts/kill-child.sh
+
 cloudron-support ALL=(ALL) NOPASSWD: ALL

src/logs.js

@@ -9,6 +9,7 @@ const assert = require('assert'),
     TransformStream = stream.Transform;
 
 const LOGTAIL_CMD = path.join(__dirname, 'scripts/logtail.sh');
+const KILL_CHILD_CMD = path.join(__dirname, 'scripts/kill-child.sh');
 
 class LogStream extends TransformStream {
     constructor(options) {
@@ -68,13 +69,12 @@ function tail(filePaths, options) {
     if (options.follow) args.push('--follow');
 
     if (options.sudo) {
-        const cp = child_process.spawn('/usr/bin/sudo', [ '-S', LOGTAIL_CMD, ...args, ...filePaths ]);
-        cp.terminate = () => { // see note in shell.js
-            child_process.spawn('kill', ['-SIGKILL', -cp.pid], { detached: true }, (error) => {
-                if (error) debug(`tail could not terminate`, error);
+        const cp = child_process.spawn('/usr/bin/sudo', [ LOGTAIL_CMD, ...args, ...filePaths ]);
+        cp.terminate = () => {
+            child_process.execFile('/usr/bin/sudo', [ KILL_CHILD_CMD, cp.pid, process.pid ], { encoding: 'utf8' }, (error, stdout, stderr) => {
+                if (error) debug(`tail: failed to kill children`, stdout, stderr);
             });
         };
-        cp.stdin.end();
         return cp;
     } else {
         const cp = child_process.spawn('/usr/bin/tail', args.concat(filePaths));
@@ -96,7 +96,7 @@ function journalctl(unit, options) {
 
     if (options.follow) args.push('--follow');
 
-    const cp = spawn('journalctl', args);
+    const cp = child_process.spawn('journalctl', args);
     cp.terminate = () => cp.kill('SIGKILL');
     return cp;
 }

src/scripts/kill-child.sh

@@ -0,0 +1,46 @@
+#!/bin/bash
+
+set -eu -o pipefail
+
+if [[ ${EUID} -ne 0 ]]; then
+    echo "This script should be run as root." > /dev/stderr
+    exit 1
+fi
+
+if [[ $# -eq 0 ]]; then
+    echo "No arguments supplied"
+    exit 1
+fi
+
+if [[ "$1" == "--check" ]]; then
+    echo "OK"
+    exit 0
+fi
+
+function killtree() {
+    local pid=$1
+    for cpid in $(pgrep -P "$pid"); do
+        killtree "${cpid}" || true
+    done
+    echo "kill-child: killing $pid"
+    kill -SIGKILL "${pid}" 2>/dev/null || true
+}
+
+readonly target_pid="$1"
+readonly expected_parent_pid="$2"
+
+readonly target_actual_parent_pid=$(ps -o ppid= -p "${target_pid}" 2>/dev/null | tr -d ' ')
+
+if [[ -z "${target_actual_parent_pid}" ]]; then
+  echo "kill-child: target PID ${target_pid} does not exist."
+  exit 1
+fi
+
+if [[ "${target_actual_parent_pid}" -ne "${expected_parent_pid}" ]]; then
+  echo "kill-child: refusing to kill — PID ${target_pid} is not a child of ${expected_parent_pid}."
+  exit 1
+fi
+
+readonly child_cmd=$(ps -o cmd= -p "${target_pid}")
+echo "kill-child: kill PID ${target_pid} (command: ${child_cmd})"
+killtree ${target_pid}