fix(fleet): resolve-then-validate symlink guard + framework helper resolution (#1380) (#1383)

Co-authored-by: code-be-01 <[email protected]>

packages/mosaic/src/fleet/secure-file.spec.ts

@@ -10,12 +10,14 @@ import {
   type PathLike,
 } from 'node:fs';
 import type * as NodeFs from 'node:fs';
+import type { Stats } from 'node:fs';
 import { tmpdir } from 'node:os';
-import { join } from 'node:path';
+import { join, resolve } from 'node:path';
 
 interface FilesystemRaceState {
   afterLstat?: (path: string) => void;
   afterOpen?: (path: string) => void;
+  afterStat?: (path: string, stats: Stats) => Stats;
 }
 
 const filesystemRaceState = vi.hoisted<FilesystemRaceState>(() => ({}));
@@ -29,6 +31,10 @@ vi.mock('node:fs', async (importOriginal) => {
       filesystemRaceState.afterLstat?.(String(path));
       return result;
     },
+    statSync: (path: PathLike) => {
+      const result = actual.statSync(path);
+      return filesystemRaceState.afterStat?.(String(path), result) ?? result;
+    },
     openSync: (path: PathLike, flags: string | number, mode?: number) => {
       const fd = actual.openSync(path, flags, mode);
       filesystemRaceState.afterOpen?.(String(path));
@@ -46,11 +52,13 @@ describe('secure file reads', () => {
     root = mkdtempSync(join(tmpdir(), 'mosaic-secure-file-'));
     filesystemRaceState.afterLstat = undefined;
     filesystemRaceState.afterOpen = undefined;
+    filesystemRaceState.afterStat = undefined;
   });
 
   afterEach(() => {
     filesystemRaceState.afterLstat = undefined;
     filesystemRaceState.afterOpen = undefined;
+    filesystemRaceState.afterStat = undefined;
     rmSync(root, { recursive: true, force: true });
   });
 
@@ -60,27 +68,89 @@ describe('secure file reads', () => {
     );
   });
 
-  it('rejects a symlink in a file ancestor', () => {
+  // stack#1380: the guard resolves symlinks and validates the resolved target
+  // instead of refusing any symlink component.
+  it('permits a symlink ancestor whose resolved target is inside the root', () => {
     const external = join(root, 'external');
     mkdirSync(external);
     writeFileSync(join(external, 'file'), 'external\n');
     symlinkSync(external, join(root, 'linked'));
 
-    expect(() => readRegularFileSecure(join(root, 'linked', 'file'), { root })).toThrow(
-      'path ancestor is a symbolic link',
-    );
+    const snapshot = readRegularFileSecure(join(root, 'linked', 'file'), { root });
+    expect(snapshot.content.toString('utf8')).toBe('external\n');
   });
 
-  it('rejects a symlink target', () => {
-    const external = join(root, 'external');
+  it('permits a symlinked file whose resolved target is inside the root', () => {
+    const external = join(root, 'external-file');
     writeFileSync(external, 'external\n');
     symlinkSync(external, join(root, 'linked-file'));
 
-    expect(() => readRegularFileSecure(join(root, 'linked-file'), { root })).toThrow(
-      'file is a symbolic link',
+    const snapshot = readRegularFileSecure(join(root, 'linked-file'), { root });
+    expect(snapshot.content.toString('utf8')).toBe('external\n');
+  });
+
+  it('permits a symlink resolving into an additional sanctioned root (split-home roster shape)', () => {
+    const brain = `${root}-brain`;
+    mkdirSync(join(brain, 'fleet'), { recursive: true });
+    writeFileSync(join(brain, 'fleet', 'roster.yaml'), 'roster\n', { mode: 0o600 });
+    mkdirSync(join(root, 'fleet'));
+    symlinkSync(join(brain, 'fleet', 'roster.yaml'), join(root, 'fleet', 'roster.yaml'));
+
+    const snapshot = readRegularFileSecure(join(root, 'fleet', 'roster.yaml'), {
+      root,
+      symlinkTargetRoots: [brain],
+    });
+    expect(snapshot.content.toString('utf8')).toBe('roster\n');
+  });
+
+  it('refuses a symlink whose resolved target escapes every sanctioned root', () => {
+    const outside = mkdtempSync(join(tmpdir(), 'mosaic-secure-outside-'));
+    try {
+      mkdirSync(join(root, 'fleet'), { recursive: true });
+      writeFileSync(join(outside, 'roster.yaml'), 'escaped\n', { mode: 0o600 });
+      symlinkSync(join(outside, 'roster.yaml'), join(root, 'fleet', 'roster.yaml'));
+
+      expect(() => readRegularFileSecure(join(root, 'fleet', 'roster.yaml'), { root })).toThrow(
+        /symlink target escapes managed roots/,
+      );
+    } finally {
+      rmSync(outside, { recursive: true, force: true });
+    }
+  });
+
+  it('refuses a group-writable symlink target', () => {
+    const loose = join(root, 'loose');
+    mkdirSync(loose);
+    chmodSync(loose, 0o770); // group-writable bit survives umask via explicit chmod
+    writeFileSync(join(loose, 'file'), 'loose\n');
+    symlinkSync(loose, join(root, 'linked-loose'));
+
+    expect(() => readRegularFileSecure(join(root, 'linked-loose', 'file'), { root })).toThrow(
+      /group- or world-writable/,
     );
   });
 
+  it('refuses a symlink target owned by another user', () => {
+    const external = join(root, 'foreign');
+    mkdirSync(external);
+    writeFileSync(join(external, 'file'), 'foreign\n');
+    symlinkSync(external, join(root, 'linked-foreign'));
+
+    filesystemRaceState.afterStat = (path, stats): Stats => {
+      if (resolve(path) === resolve(external)) {
+        return { ...stats, uid: stats.uid + 4242 } as Stats;
+      }
+      return stats;
+    };
+    try {
+      expect(() => readRegularFileSecure(join(root, 'linked-foreign', 'file'), { root })).toThrow(
+        /not owned by the current user/,
+      );
+    } finally {
+      filesystemRaceState.afterStat = undefined;
+    }
+  });
+
   it('keeps ancestor traversal bound when an opened directory is substituted', () => {
     const tools = join(root, 'tools');
     const displacedTools = join(root, 'tools.displaced');