fix(TaskProcessing): restrict allowed_classes in Manager cache deserialization

[XananasX7]

Summary

OC\TaskProcessing\Manager::getAvailableTaskTypes() deserializes the task type cache from the distributed cache backend without restricting which PHP classes can be instantiated.

The issue

$cachedValue = $this->distributedCache->get($cacheKey);
if ($cachedValue !== null) {
    $this->availableTaskTypes = unserialize($cachedValue);  // ← no allowed_classes
}

The serialized data contains ShapeDescriptor objects, ShapeEnumValue objects, and EShapeType enum values. An attacker who can write to the cache backend (e.g., Redis without authentication or with weak ACLs — a common misconfiguration in cloud deployments) can inject a PHP gadget chain and achieve Remote Code Execution via PHP Object Injection.

The fix

Restrict unserialize() to only the three known classes actually stored in the cache:

$this->availableTaskTypes = unserialize($cachedValue, [
    'allowed_classes' => [
        ShapeDescriptor::class,
        ShapeEnumValue::class,
        EShapeType::class,
    ],
]);

This is verified by inspecting the write path: serialize($this->availableTaskTypes) where $availableTaskTypes is built from getInputShape(), getOutputShape() etc. which return arrays of ShapeDescriptor objects with EShapeType values.

Security impact

Redis Object Injection via unprotected cache backends is a well-known attack class. Nextcloud already uses allowed_classes in FileProfilerStorage, CommandJob, and QueueBus — this PR extends the same pattern to TaskProcessing\Manager.

Signed-off-by: XananasX7

[miaulalala]

Can you please run the php linter by running composer cs:fix

Add your changes, then amend you last commit by running:

git commit --amend --signoff

and then push:

git push --force-with-lease

which will fix the CI issues.

[julien-nc]

From Php doc:

Warning Do not pass untrusted user input to unserialize() regardless of the options value of allowed_classes. Unserialization can result in code being loaded and executed due to object instantiation and autoloading, and a malicious user may be able to exploit this.

@marcelklehr Wdyt? Are we good with the allowed classes?

[marcelklehr]

Are we good with the allowed classes?

Yes, these do not have any constructor code with side effects