harden buildx scoped config path handling

__tests__/context.test.ts

@@ -35,6 +35,87 @@ test('getAuthList uses the default Docker Hub registry when computing scoped con
   });
 });
 
+test('getAuthList supports @ scopes appended to the registry config dir', async () => {
+  process.env['INPUT_USERNAME'] = 'dbowie';
+  process.env['INPUT_PASSWORD'] = 'groundcontrol';
+  process.env['INPUT_SCOPE'] = '@push';
+  process.env['INPUT_LOGOUT'] = 'false';
+  const [auth] = getAuthList(getInputs());
+  expect(auth).toMatchObject({
+    configDir: path.join(Buildx.configDir, 'config', 'registry-1.docker.io') + '@push'
+  });
+});
+
+test('getAuthList supports repository scopes with appended actions', async () => {
+  process.env['INPUT_USERNAME'] = 'dbowie';
+  process.env['INPUT_PASSWORD'] = 'groundcontrol';
+  process.env['INPUT_SCOPE'] = 'docker/buildx-bin@push';
+  process.env['INPUT_LOGOUT'] = 'false';
+  const [auth] = getAuthList(getInputs());
+  expect(auth).toMatchObject({
+    configDir: path.join(Buildx.configDir, 'config', 'registry-1.docker.io', 'docker', 'buildx-bin@push')
+  });
+});
+
+test('getAuthList supports comma-separated scope actions', async () => {
+  process.env['INPUT_USERNAME'] = 'dbowie';
+  process.env['INPUT_PASSWORD'] = 'groundcontrol';
+  process.env['INPUT_SCOPE'] = 'docker/buildx-bin@pull,push';
+  process.env['INPUT_LOGOUT'] = 'false';
+  const [auth] = getAuthList(getInputs());
+  expect(auth).toMatchObject({
+    configDir: path.join(Buildx.configDir, 'config', 'registry-1.docker.io', 'docker', 'buildx-bin@pull,push')
+  });
+});
+
+// prettier-ignore
+test.each([
+  '../../../../work/leaked',
+  '..',
+  'foo/../../../../etc',
+  '@../../../leaked',
+  'foo/bar@../../../leaked',
+  '@push@pull',
+  'foo/bar@push@pull',
+  '@push,',
+  '@,push',
+  '@pull,,push',
+  '@Push',
+  path.join(path.parse(Buildx.configDir).root, 'work', 'leaked')
+])('getAuthList rejects unsafe or unsupported scope path: %s', async scope => {
+  expect(() => {
+    getAuthList({
+      registry: '',
+      username: 'dbowie',
+      password: 'groundcontrol',
+      scope,
+      ecr: '',
+      logout: false,
+      registryAuth: ''
+    });
+  }).toThrow(/Invalid scope/);
+});
+
+// prettier-ignore
+test.each([
+  '../../../../work/leaked',
+  '..',
+  'foo/../../../../etc',
+  path.join(path.parse(Buildx.configDir).root, 'work', 'leaked')
+])('getAuthList rejects unsafe registry path: %s', async registry => {
+  expect(() => {
+    getAuthList({
+      registry,
+      username: 'dbowie',
+      password: 'groundcontrol',
+      scope: '@push',
+      ecr: '',
+      logout: false,
+      registryAuth: ''
+    });
+  }).toThrow(/Invalid registry/);
+});
+
 test('getAuthList skips secret masking when registry-auth password is absent', async () => {
   const stdoutWriteSpy = vi.spyOn(process.stdout, 'write').mockImplementation(() => true);
   const [auth] = getAuthList({

src/context.ts

@@ -77,13 +77,33 @@ export function scopeToConfigDir(registry: string, scope?: string): string {
   if (scopeDisabled() || !scope || scope === '') {
     return '';
   }
-  let configDir = path.join(Buildx.configDir, 'config', registry === 'docker.io' ? 'registry-1.docker.io' : registry);
-  if (scope.startsWith('@')) {
-    configDir += scope;
-  } else {
-    configDir = path.join(configDir, scope);
+  const configRoot = path.resolve(Buildx.configDir, 'config');
+  const registryDir = path.resolve(configRoot, registry === 'docker.io' ? 'registry-1.docker.io' : registry);
+  if (!isChildPath(configRoot, registryDir)) {
+    throw new Error(`Invalid registry '${registry}': resolved config path escapes the Buildx config directory`);
+  }
+  const scopeParts = scope.split('@');
+  if (scopeParts.length > 2) {
+    throw new Error(`Invalid scope '${scope}': scope can contain at most one @ separator`);
+  }
+  const [scopePath, scopeActions] = scopeParts;
+  if (scopeActions !== undefined && !/^[a-z]+(,[a-z]+)*$/.test(scopeActions)) {
+    throw new Error(`Invalid scope '${scope}': scope actions must be lowercase names separated by commas`);
+  }
+  const scopeSuffix = scopeActions === undefined ? '' : `@${scopeActions}`;
+  if (scopePath === '') {
+    return `${registryDir}${scopeSuffix}`;
   }
-  return configDir;
+  const configDir = path.resolve(registryDir, scopePath);
+  if (!isChildPath(registryDir, configDir)) {
+    throw new Error(`Invalid scope '${scope}': resolved config path escapes the Buildx config directory`);
+  }
+  return `${configDir}${scopeSuffix}`;
+}
+
+function isChildPath(parent: string, child: string): boolean {
+  const relativePath = path.relative(parent, child);
+  return relativePath !== '' && relativePath !== '..' && !relativePath.startsWith(`..${path.sep}`) && !path.isAbsolute(relativePath);
 }
 
 function scopeDisabled(): boolean {