From ff17ec2cd143ba9129f39995265094a2e199d7e6 Mon Sep 17 00:00:00 2001
From: Eli Bosley <eli@bosley.dev>
Date: Wed, 15 Jul 2026 22:47:05 -0400
Subject: [PATCH] fix(downgrade): block during protected array shrink

---
 .../include/Downgrade.php                     | 21 ++++++++++
 .../include/ParityProtectedShrinkGuard.php    | 22 +++++++++++
 .../parity_protected_shrink_guard_test.php    | 39 +++++++++++++++++++
 3 files changed, 82 insertions(+)
 create mode 100644 emhttp/plugins/dynamix.plugin.manager/include/ParityProtectedShrinkGuard.php
 create mode 100644 emhttp/plugins/dynamix.plugin.manager/tests/parity_protected_shrink_guard_test.php

diff --git a/emhttp/plugins/dynamix.plugin.manager/include/Downgrade.php b/emhttp/plugins/dynamix.plugin.manager/include/Downgrade.php
index 9742e7bbc3..4d183e1dac 100644
--- a/emhttp/plugins/dynamix.plugin.manager/include/Downgrade.php
+++ b/emhttp/plugins/dynamix.plugin.manager/include/Downgrade.php
@@ -14,11 +14,32 @@
 $docroot ??= ($_SERVER['DOCUMENT_ROOT'] ?: '/usr/local/emhttp');
 require_once "$docroot/webGui/include/Wrappers.php";
 require_once "$docroot/webGui/include/Secure.php";
+require_once __DIR__.'/ParityProtectedShrinkGuard.php';
 
 // add translations
 $_SERVER['REQUEST_URI'] = 'plugins';
 require_once "$docroot/webGui/include/Translations.php";
 
+$protectedShrinkFiles = parity_protected_shrink_files();
+$downgradeMarker = '/var/run/unraid-os-downgrade';
+$downgradeMarkerHandle = @fopen($downgradeMarker, 'x');
+
+if ($downgradeMarkerHandle === false) {
+  http_response_code(409);
+  echo _('An Unraid downgrade is already pending.');
+  exit;
+}
+
+fclose($downgradeMarkerHandle);
+chmod($downgradeMarker, 0600);
+
+if (parity_protected_shrink_active($protectedShrinkFiles)) {
+  unlink($downgradeMarker);
+  http_response_code(409);
+  echo _('Finish or recover the active parity-protected disk removal before downgrading Unraid.');
+  exit;
+}
+
 $tmpdir="/boot/deletemedowngrade.".uniqid();
 mkdir($tmpdir);
 exec("mv -f /boot/bz* $tmpdir");
diff --git a/emhttp/plugins/dynamix.plugin.manager/include/ParityProtectedShrinkGuard.php b/emhttp/plugins/dynamix.plugin.manager/include/ParityProtectedShrinkGuard.php
new file mode 100644
index 0000000000..0cc25b952a
--- /dev/null
+++ b/emhttp/plugins/dynamix.plugin.manager/include/ParityProtectedShrinkGuard.php
@@ -0,0 +1,22 @@
+<?PHP
+
+function parity_protected_shrink_files($bootConfigRoot = '/boot/config') {
+  $bootConfigRoot = rtrim($bootConfigRoot, '/');
+
+  return [
+    "$bootConfigRoot/unraid/storage/parity-protected-shrink.json",
+    "$bootConfigRoot/storage/parity-protected-shrink-prepared",
+    "$bootConfigRoot/storage/parity-protected-shrink-prepared-complete",
+    "$bootConfigRoot/storage/parity-protected-shrink-daemon",
+  ];
+}
+
+function parity_protected_shrink_active($protectedShrinkFiles) {
+  foreach ($protectedShrinkFiles as $protectedShrinkFile) {
+    if (is_file($protectedShrinkFile)) return true;
+  }
+
+  return false;
+}
+
+?>
diff --git a/emhttp/plugins/dynamix.plugin.manager/tests/parity_protected_shrink_guard_test.php b/emhttp/plugins/dynamix.plugin.manager/tests/parity_protected_shrink_guard_test.php
new file mode 100644
index 0000000000..2b9d53aa7c
--- /dev/null
+++ b/emhttp/plugins/dynamix.plugin.manager/tests/parity_protected_shrink_guard_test.php
@@ -0,0 +1,39 @@
+<?PHP
+
+require_once __DIR__.'/../include/ParityProtectedShrinkGuard.php';
+
+function assert_same($expected, $actual, $message) {
+  if ($expected !== $actual) {
+    fwrite(STDERR, "$message\nExpected: ".var_export($expected, true)."\nActual: ".var_export($actual, true)."\n");
+    exit(1);
+  }
+}
+
+$productionFiles = parity_protected_shrink_files();
+assert_same(
+  '/boot/config/unraid/storage/parity-protected-shrink.json',
+  $productionFiles[0],
+  'The downgrade guard must use the production Core intent path.'
+);
+
+$testRoot = sys_get_temp_dir().'/parity-protected-shrink-guard-'.bin2hex(random_bytes(8));
+$testFiles = parity_protected_shrink_files($testRoot);
+mkdir(dirname($testFiles[0]), 0700, true);
+mkdir(dirname($testFiles[1]), 0700, true);
+
+assert_same(false, parity_protected_shrink_active($testFiles), 'No proof must report idle.');
+file_put_contents($testFiles[0], '{}');
+assert_same(true, parity_protected_shrink_active($testFiles), 'A Core intent must block downgrade.');
+unlink($testFiles[0]);
+file_put_contents($testFiles[2], 'stage=prepared\n');
+assert_same(true, parity_protected_shrink_active($testFiles), 'A daemon proof must block downgrade.');
+
+unlink($testFiles[2]);
+rmdir(dirname($testFiles[0]));
+rmdir(dirname(dirname($testFiles[0])));
+rmdir(dirname($testFiles[1]));
+rmdir($testRoot);
+
+echo "parity protected shrink downgrade guard: ok\n";
+
+?>