fix(core): resolve symlinks for non-existent paths during validation (#21487)

Author: Adib234

packages/core/src/config/config.ts

@@ -6,7 +6,6 @@
 
 import * as fs from 'node:fs';
 import * as path from 'node:path';
-import * as os from 'node:os';
 import { inspect } from 'node:util';
 import process from 'node:process';
 import type {
@@ -135,7 +134,7 @@ import { SkillManager, type SkillDefinition } from '../skills/skillManager.js';
 import { startupProfiler } from '../telemetry/startupProfiler.js';
 import type { AgentDefinition } from '../agents/types.js';
 import { fetchAdminControls } from '../code_assist/admin/admin_controls.js';
-import { isSubpath } from '../utils/paths.js';
+import { isSubpath, resolveToRealPath } from '../utils/paths.js';
 import { UserHintService } from './userHintService.js';
 import { WORKSPACE_POLICY_TIER } from '../policy/config.js';
 import { loadPoliciesFromToml } from '../policy/toml-loader.js';
@@ -2345,25 +2344,15 @@ export class Config implements McpContext {
    * @returns true if the path is allowed, false otherwise.
    */
   isPathAllowed(absolutePath: string): boolean {
-    const realpath = (p: string) => {
-      let resolved: string;
-      try {
-        resolved = fs.realpathSync(p);
-      } catch {
-        resolved = path.resolve(p);
-      }
-      return os.platform() === 'win32' ? resolved.toLowerCase() : resolved;
-    };
-
-    const resolvedPath = realpath(absolutePath);
+    const resolvedPath = resolveToRealPath(absolutePath);
 
     const workspaceContext = this.getWorkspaceContext();
     if (workspaceContext.isPathWithinWorkspace(resolvedPath)) {
       return true;
     }
 
     const projectTempDir = this.storage.getProjectTempDir();
-    const resolvedTempDir = realpath(projectTempDir);
+    const resolvedTempDir = resolveToRealPath(projectTempDir);
 
     return isSubpath(resolvedTempDir, resolvedPath);
   }

packages/core/src/config/storage.test.ts

@@ -24,7 +24,7 @@ vi.mock('fs', async (importOriginal) => {
 });
 
 import { Storage } from './storage.js';
-import { GEMINI_DIR, homedir } from '../utils/paths.js';
+import { GEMINI_DIR, homedir, resolveToRealPath } from '../utils/paths.js';
 import { ProjectRegistry } from './projectRegistry.js';
 import { StorageMigration } from './storageMigration.js';
 
@@ -279,8 +279,7 @@ describe('Storage – additional helpers', () => {
         name: 'custom absolute path outside throws',
         customDir: '/absolute/path/to/plans',
         expected: '',
-        expectedError:
-          "Custom plans directory '/absolute/path/to/plans' resolves to '/absolute/path/to/plans', which is outside the project root '/tmp/project'.",
+        expectedError: `Custom plans directory '/absolute/path/to/plans' resolves to '/absolute/path/to/plans', which is outside the project root '${resolveToRealPath(projectRoot)}'.`,
       },
       {
         name: 'absolute path that happens to be inside project root',
@@ -306,8 +305,7 @@ describe('Storage – additional helpers', () => {
         name: 'escaping relative path throws',
         customDir: '../escaped-plans',
         expected: '',
-        expectedError:
-          "Custom plans directory '../escaped-plans' resolves to '/tmp/escaped-plans', which is outside the project root '/tmp/project'.",
+        expectedError: `Custom plans directory '../escaped-plans' resolves to '${resolveToRealPath(path.resolve(projectRoot, '../escaped-plans'))}', which is outside the project root '${resolveToRealPath(projectRoot)}'.`,
       },
       {
         name: 'hidden directory starting with ..',

packages/core/src/utils/paths.test.ts

@@ -510,9 +510,11 @@ describe('resolveToRealPath', () => {
     expect(resolveToRealPath(input)).toBe(expected);
   });
 
-  it('should return decoded path even if fs.realpathSync fails', () => {
+  it('should return decoded path even if fs.realpathSync fails with ENOENT', () => {
     vi.spyOn(fs, 'realpathSync').mockImplementationOnce(() => {
-      throw new Error('File not found');
+      const err = new Error('File not found') as NodeJS.ErrnoException;
+      err.code = 'ENOENT';
+      throw err;
     });
 
     const p = path.resolve('path', 'to', 'New Project');
@@ -521,6 +523,25 @@ describe('resolveToRealPath', () => {
 
     expect(resolveToRealPath(input)).toBe(expected);
   });
+
+  it('should recursively resolve symlinks for non-existent child paths', () => {
+    const parentPath = path.resolve('/some/parent/path');
+    const resolvedParentPath = path.resolve('/resolved/parent/path');
+    const childPath = path.resolve(parentPath, 'child', 'file.txt');
+    const expectedPath = path.resolve(resolvedParentPath, 'child', 'file.txt');
+
+    vi.spyOn(fs, 'realpathSync').mockImplementation((p) => {
+      const pStr = p.toString();
+      if (pStr === parentPath) {
+        return resolvedParentPath;
+      }
+      const err = new Error('ENOENT') as NodeJS.ErrnoException;
+      err.code = 'ENOENT';
+      throw err;
+    });
+
+    expect(resolveToRealPath(childPath)).toBe(expectedPath);
+  });
 });
 
 describe('normalizePath', () => {

packages/core/src/utils/paths.ts

@@ -359,8 +359,8 @@ export function isSubpath(parentPath: string, childPath: string): boolean {
  * @param pathStr The path string to resolve.
  * @returns The resolved real path.
  */
-export function resolveToRealPath(path: string): string {
-  let resolvedPath = path;
+export function resolveToRealPath(pathStr: string): string {
+  let resolvedPath = pathStr;
 
   try {
     if (resolvedPath.startsWith('file://')) {
@@ -372,11 +372,28 @@ export function resolveToRealPath(path: string): string {
     // Ignore error (e.g. malformed URI), keep path from previous step
   }
 
+  return robustRealpath(path.resolve(resolvedPath));
+}
+
+function robustRealpath(p: string): string {
   try {
-    return fs.realpathSync(resolvedPath);
-  } catch (_e) {
-    // If realpathSync fails, it might be because the path doesn't exist.
-    // In that case, we can fall back to the path processed.
-    return resolvedPath;
+    return fs.realpathSync(p);
+  } catch (e: unknown) {
+    if (e && typeof e === 'object' && 'code' in e && e.code === 'ENOENT') {
+      try {
+        const stat = fs.lstatSync(p);
+        if (stat.isSymbolicLink()) {
+          const target = fs.readlinkSync(p);
+          const resolvedTarget = path.resolve(path.dirname(p), target);
+          return robustRealpath(resolvedTarget);
+        }
+      } catch {
+        // Not a symlink, or lstat failed. Just resolve parent.
+      }
+      const parent = path.dirname(p);
+      if (parent === p) return p;
+      return path.join(robustRealpath(parent), path.basename(p));
+    }
+    throw e;
   }
 }

packages/core/src/utils/workspaceContext.ts

@@ -4,10 +4,10 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { isNodeError } from '../utils/errors.js';
 import * as fs from 'node:fs';
 import * as path from 'node:path';
 import { debugLogger } from './debugLogger.js';
+import { resolveToRealPath } from './paths.js';
 
 export type Unsubscribe = () => void;
 
@@ -227,22 +227,7 @@ export class WorkspaceContext {
    * if it did exist.
    */
   private fullyResolvedPath(pathToCheck: string): string {
-    try {
-      return fs.realpathSync(path.resolve(this.targetDir, pathToCheck));
-    } catch (e: unknown) {
-      if (
-        isNodeError(e) &&
-        e.code === 'ENOENT' &&
-        e.path &&
-        // realpathSync does not set e.path correctly for symlinks to
-        // non-existent files.
-        !this.isFileSymlink(e.path)
-      ) {
-        // If it doesn't exist, e.path contains the fully resolved path.
-        return e.path;
-      }
-      throw e;
-    }
+    return resolveToRealPath(path.resolve(this.targetDir, pathToCheck));
   }
 
   /**
@@ -262,15 +247,4 @@ export class WorkspaceContext {
       !path.isAbsolute(relative)
     );
   }
-
-  /**
-   * Checks if a file path is a symbolic link that points to a file.
-   */
-  private isFileSymlink(filePath: string): boolean {
-    try {
-      return !fs.readlinkSync(filePath).endsWith('/');
-    } catch (_error) {
-      return false;
-    }
-  }
 }