Don't follow symlinks when checking for lockfiles

The Supervisor should only care whether a lockfile exists or
not. This also fixes an edge case where a user symlinked a lockfile
to a nonexistent file, causing the Supervisor to enter an error
loop as it was not able to `stat` the nonexistent file.

Change-type: patch
Signed-off-by: Christina Ying Wang <christina@balena.io>

src/lib/lockfile.ts

@@ -29,8 +29,10 @@ export const getLocksTaken = async (
 	}
 	for (const fileOrDir of filesOrDirs) {
 		const lockPath = `${rootDir}/${fileOrDir.name}`;
-		// A lock is taken if it's a file or directory within rootDir that passes filter fn
-		if (lockFilter(lockPath, await fs.stat(lockPath))) {
+		// A lock is taken if it's a file or directory within rootDir that passes filter fn.
+		// We also don't want to follow symlinks since we don't want to follow the lock to
+		// the target path if it's a symlink and only care that it exists or not.
+		if (lockFilter(lockPath, await fs.lstat(lockPath))) {
 			locksTaken.push(lockPath);
 			// Otherwise, if non-lock directory, seek locks recursively within directory
 		} else if (fileOrDir.isDirectory()) {

test/integration/lib/lockfile.spec.ts

@@ -226,4 +226,18 @@ describe('lib/lockfile', () => {
 		// Clean up locks
 		await fs.rm(`${lockdir}`, { recursive: true });
 	});
+
+	// This tests an edge case where the lockfile is a symlink to a nonexistent file.
+	// Calling fs.stat on such a lockfile will throw, hence why we switched to fs.lstat.
+	it('should not error if lockfile is a symlink to a nonexistent file', async () => {
+		// Create symlink lock
+		await fs.symlink('/nonexistent', `${lockdir}/updates.lock`);
+
+		expect(
+			await lockfile.getLocksTaken(lockdir, (_p, s) => s.isSymbolicLink()),
+		).to.have.members([`${lockdir}/updates.lock`]);
+
+		// Cleanup symlink lock
+		await fs.rm(`${lockdir}/updates.lock`);
+	});
 });