fix(session): Make session encryption more robust #47396
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,144 @@ | ||
| <?php | ||
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| declare(strict_types=1); | ||
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| /** | ||
| * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors | ||
| * SPDX-License-Identifier: AGPL-3.0-only | ||
| */ | ||
|
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| namespace OC\Session; | ||
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| use Exception; | ||
| use OCP\IRequest; | ||
| use OCP\Security\ICrypto; | ||
| use OCP\Security\ISecureRandom; | ||
| use SessionHandler; | ||
| use function explode; | ||
| use function implode; | ||
| use function json_decode; | ||
| use function OCP\Log\logger; | ||
| use function session_decode; | ||
| use function session_encode; | ||
|
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| class CryptoSessionHandler extends SessionHandler { | ||
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| public function __construct(private ISecureRandom $secureRandom, | ||
| private ICrypto $crypto, | ||
| private IRequest $request) { | ||
| } | ||
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| /** | ||
| * @param string $id | ||
| * | ||
| * @return array{0: string, 1: ?string} | ||
| */ | ||
| private function parseId(string $id): array { | ||
| $parts = explode('|', $id); | ||
| return [$parts[0], $parts[1]]; | ||
| } | ||
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| public function create_sid(): string { | ||
| $id = parent::create_sid(); | ||
| $passphrase = $this->secureRandom->generate(128); | ||
| return implode('|', [$id, $passphrase]); | ||
| } | ||
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| /** | ||
| * Read and decrypt session data | ||
| * | ||
| * The decryption passphrase is encoded in the id since Nextcloud 31. For | ||
| * backwards compatibility after upgrade we also read the pass phrase from | ||
| * the old cookie and try to restore session from the legacy format. | ||
| * | ||
| * @param string $id | ||
| * | ||
| * @return false|string | ||
| */ | ||
| public function read(string $id): false|string { | ||
| [$sessionId, $passphrase] = $this->parseId($id); | ||
|
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| /** | ||
| * Legacy handling | ||
| * | ||
| * @TODO remove in Nextcloud 32 | ||
| */ | ||
| if ($passphrase === null) { | ||
| if (($passphrase = $this->request->getCookie(CryptoWrapper::COOKIE_NAME)) === false) { | ||
| // No passphrase in the ID or an old cookie. Time to give up. | ||
| return false; | ||
| } | ||
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| // Read the encrypted and encoded data | ||
| $serializedData = parent::read($sessionId); | ||
| if ($serializedData === '') { | ||
| // Nothing to decode or decrypt | ||
| return ''; | ||
| } | ||
| // Back up the superglobal before we decode/restore the legacy session data | ||
| // This is necessary because session_decode populates the superglobals | ||
| // We restore the old state end the end (the final block, also run in | ||
| // case of an error) | ||
| $globalBackup = $_SESSION; | ||
| try { | ||
| if (!session_decode($serializedData)) { | ||
| // Bail if we can't decode the data | ||
| return false; | ||
| } | ||
| $encryptedData = $_SESSION['encrypted_session_data']; | ||
| try { | ||
| $sessionValues = json_decode( | ||
| $this->crypto->decrypt($encryptedData, $passphrase), | ||
| true, | ||
| 512, | ||
| JSON_THROW_ON_ERROR, | ||
| ); | ||
| foreach ($sessionValues as $key => $value) { | ||
| $_SESSION[$key] = $value; | ||
| } | ||
| } catch (Exception $e) { | ||
| logger('core')->critical('Could not decrypt or decode encrypted legacy session data', [ | ||
| 'exception' => $e, | ||
| 'sessionId' => $sessionId, | ||
| ]); | ||
| } | ||
| return session_encode(); | ||
| } finally { | ||
| foreach (array_keys($_SESSION) as $key) { | ||
|
Check failure on line 107 in lib/private/Session/CryptoSessionHandler.php
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| unset($_SESSION[$key]); | ||
| } | ||
| foreach ($globalBackup as $key => $value) { | ||
| $_SESSION[$key] = $value; | ||
| } | ||
| $_SESSION = $globalBackup; | ||
| } | ||
| } | ||
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| $read = parent::read($sessionId); | ||
| return $read; | ||
| } | ||
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| /** | ||
| * Encrypt and write session data | ||
| * | ||
| * @param string $id | ||
| * @param string $data | ||
| * | ||
| * @return bool | ||
| */ | ||
| public function write(string $id, string $data): bool { | ||
| [$sessionId, $passphrase] = $this->parseId($id); | ||
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| if ($passphrase === null) { | ||
| $passphrase = $this->request->getCookie(CryptoWrapper::COOKIE_NAME); | ||
| // return false; | ||
| } | ||
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| return parent::write($sessionId, $data); | ||
| } | ||
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| public function close(): bool { | ||
|
Check failure on line 140 in lib/private/Session/CryptoSessionHandler.php
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| parent::close(); | ||
| } | ||
|
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| } | ||
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Unfortunately writing unit tests is not an option for a session handler because PHP sessions have so many side effects. E.g. an actual session has to be opened to test read/write, but you can't close and re-open the session because opening a session sets a header, and setting headers is not possible once any kind of output was written 🫠