fix: harden OpenTelemetry config writing

src/otel/index.test.ts

@@ -0,0 +1,77 @@
+import { Buffer } from 'node:buffer';
+import { describe, it } from 'node:test';
+import * as assert from 'node:assert/strict';
+import * as pulumi from '@pulumi/pulumi';
+import * as yaml from 'yaml';
+import { OtelCollector } from './index';
+
+const shellSensitiveConfig: OtelCollector.Config = {
+  receivers: {
+    otlp: {
+      protocols: {
+        http: {
+          endpoint: "0.0.0.0:4318; echo 'broken' && $HOME `whoami`",
+        },
+      },
+    },
+  },
+  processors: {},
+  exporters: {
+    debug: {
+      verbosity: "it's detailed\n$(touch /tmp/pwned) `uname`; & | > <",
+    },
+  },
+  extensions: {},
+  service: {
+    pipelines: {},
+    telemetry: {
+      logs: {
+        level: "warn: '$HOME'\nnext line",
+      },
+    },
+  },
+};
+
+describe('OtelCollector', () => {
+  it('should write collector config through a base64-decoded payload', async () => {
+    const collector = new OtelCollector(
+      'service-name',
+      'test',
+      shellSensitiveConfig,
+    );
+    const commandInput = collector.configContainer.command;
+
+    assert.ok(commandInput);
+
+    const command = await resolveCommand(commandInput);
+    const [, , script] = command;
+    const encodedConfig = Buffer.from(
+      yaml.stringify(shellSensitiveConfig),
+      'utf8',
+    ).toString('base64');
+
+    assert.deepEqual(command.slice(0, 2), ['sh', '-c']);
+    assert.match(script, /base64 -d/);
+    assert.match(script, /mktemp \/etc\/otelcol-contrib\/config\.yaml\.XXXXXX/);
+    assert.match(
+      script,
+      /mv "\$tmp_config" \/etc\/otelcol-contrib\/config\.yaml/,
+    );
+    assert.match(script, new RegExp(encodedConfig));
+    assert.doesNotMatch(script, /echo '/);
+    assert.doesNotMatch(script, /touch \/tmp\/pwned/);
+    assert.doesNotMatch(script, /whoami/);
+  });
+});
+
+async function resolveCommand(
+  input: pulumi.Input<pulumi.Input<string>[]>,
+): Promise<string[]> {
+  return new Promise<string[]>(resolve => {
+    pulumi.output(input).apply(command => {
+      resolve(command);
+
+      return command;
+    });
+  });
+}

src/otel/index.ts

@@ -1,3 +1,4 @@
+import { Buffer } from 'node:buffer';
 import * as pulumi from '@pulumi/pulumi';
 import * as aws from '@pulumi/aws';
 import * as yaml from 'yaml';
@@ -202,6 +203,22 @@ export class OtelCollector {
     ];
   }
 
+  private createConfigWriterCommand(config: OtelCollector.Config): string[] {
+    const configYaml = yaml.stringify(config);
+    const encodedConfig = Buffer.from(configYaml, 'utf8').toString('base64');
+
+    return [
+      'sh',
+      '-c',
+      [
+        'set -eu',
+        'tmp_config=$(mktemp /etc/otelcol-contrib/config.yaml.XXXXXX)',
+        `printf '%s' '${encodedConfig}' | base64 -d > "$tmp_config"`,
+        'mv "$tmp_config" /etc/otelcol-contrib/config.yaml',
+      ].join('\n'),
+    ];
+  }
+
   private createConfigContainer(
     config: pulumi.Output<OtelCollector.Config>,
     volume: pulumi.Input<string>,
@@ -210,11 +227,7 @@ export class OtelCollector {
       name: 'otel-config-writer',
       image: 'amazonlinux:latest',
       essential: false,
-      command: config.apply(config => [
-        'sh',
-        '-c',
-        `echo '${yaml.stringify(config)}' > /etc/otelcol-contrib/config.yaml`,
-      ]),
+      command: config.apply(config => this.createConfigWriterCommand(config)),
       mountPoints: [
         {
           sourceVolume: volume,