nextcloud/apps/files_encryption/lib/stream.php

<?php
/**
 * @author Björn Schießle <schiessle@owncloud.com>
 * @author Florin Peter <github@florin-peter.de>
 * @author jknockaert <jasper@knockaert.nl>
 * @author Joas Schilling <nickvergessen@owncloud.com>
 * @author Morris Jobke <hey@morrisjobke.de>
 * @author Robin McCorkell <rmccorkell@karoshi.org.uk>
 * @author Sam Tuke <mail@samtuke.com>
 * @author Vincent Petry <pvince81@owncloud.com>
 *
 * @copyright Copyright (c) 2015, ownCloud, Inc.
 * @license AGPL-3.0
 *
 * This code is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License, version 3,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License, version 3,
 * along with this program.  If not, see <http://www.gnu.org/licenses/>
 *
 */

/**
 * transparently encrypted filestream
 *
 * you can use it as wrapper around an existing stream by setting CryptStream::$sourceStreams['foo']=array('path'=>$path,'stream'=>$stream)
 * and then fopen('crypt://streams/foo');
 */

namespace OCA\Files_Encryption;

use OCA\Files_Encryption\Exception\EncryptionException;

/**
 * Provides 'crypt://' stream wrapper protocol.
 * @note We use a stream wrapper because it is the most secure way to handle
 * decrypted content transfers. There is no safe way to decrypt the entire file
 * somewhere on the server, so we have to encrypt and decrypt blocks on the fly.
 * @note Paths used with this protocol MUST BE RELATIVE. Use URLs like:
 * crypt://filename, or crypt://subdirectory/filename, NOT
 * crypt:///home/user/owncloud/data. Otherwise keyfiles will be put in
 * [owncloud]/data/user/files_encryption/keyfiles/home/user/owncloud/data and
 * will not be accessible to other methods.
 * @note Data read and written must always be 8192 bytes long, as this is the
 * buffer size used internally by PHP. The encryption process makes the input
 * data longer, and input is chunked into smaller pieces in order to result in
 * a 8192 encrypted block size.
 * @note When files are deleted via webdav, or when they are updated and the
 * previous version deleted, this is handled by OC\Files\View, and thus the
 * encryption proxies are used and keyfiles deleted.
 */
class Stream {

	const PADDING_CHAR = '-';

	private $plainKey;
	private $encKeyfiles;
	private $rawPath; // The raw path relative to the data dir
	private $relPath; // rel path to users file dir
	private $userId;
	private $keyId;
	private $handle; // Resource returned by fopen
	private $meta = array(); // Header / meta for source stream
	private $cache; // Current block unencrypted
	private $position; // Current pointer position in the unencrypted stream
	private $writeFlag; // Flag to write current block when leaving it
	private $size;
	private $headerSize = 0; // Size of header
	private $unencryptedSize;
	private $publicKey;
	private $encKeyfile;
	private $newFile; // helper var, we only need to write the keyfile for new files
	private $isLocalTmpFile = false; // do we operate on a local tmp file
	private $localTmpFile; // path of local tmp file
	private $containHeader = false; // the file contain a header
	private $cipher; // cipher used for encryption/decryption
	/** @var \OCA\Files_Encryption\Util */
	private $util;

	/**
	 * @var \OC\Files\View
	 */
	private $rootView; // a fsview object set to '/'

	/**
	 * @var \OCA\Files_Encryption\Session
	 */
	private $session;
	private $privateKey;

	/**
	 * @param string $path raw path relative to data/
	 * @param string $mode
	 * @param int $options
	 * @param string $opened_path
	 * @return bool
	 * @throw \OCA\Files_Encryption\Exception\EncryptionException
	 */
	public function stream_open($path, $mode, $options, &$opened_path) {

		// read default cipher from config
		$this->cipher = Helper::getCipher();

		// assume that the file already exist before we decide it finally in getKey()
		$this->newFile = false;

		$this->rootView = new \OC\Files\View('/');

		$this->session = new Session($this->rootView);

		$this->privateKey = $this->session->getPrivateKey();
		if ($this->privateKey === false) {
			throw new EncryptionException('Session does not contain a private key, maybe your login password changed?',
					EncryptionException::PRIVATE_KEY_MISSING);
		}

		$normalizedPath = \OC\Files\Filesystem::normalizePath(str_replace('crypt://', '', $path));
		$originalFile = Helper::getPathFromTmpFile($normalizedPath);
		if ($originalFile) {
			$this->rawPath = $originalFile;
			$this->isLocalTmpFile = true;
			$this->localTmpFile = $normalizedPath;
		} else {
			$this->rawPath = $normalizedPath;
		}

		$this->util = new Util($this->rootView, Helper::getUser($this->rawPath));

		// get the key ID which we want to use, can be the users key or the
		// public share key
		$this->keyId = $this->util->getKeyId();

		$fileType = Helper::detectFileType($this->rawPath);

		switch ($fileType) {
			case Util::FILE_TYPE_FILE:
				$this->relPath = Helper::stripUserFilesPath($this->rawPath);
				$user = \OC::$server->getUserSession()->getUser();
				$this->userId = $user ? $user->getUID() : Helper::getUserFromPath($this->rawPath);
				break;
			case Util::FILE_TYPE_VERSION:
				$this->relPath = Helper::getPathFromVersion($this->rawPath);
				$this->userId = Helper::getUserFromPath($this->rawPath);
				break;
			case Util::FILE_TYPE_CACHE:
				$this->relPath = Helper::getPathFromCachedFile($this->rawPath);
				Helper::mkdirr($this->rawPath, new \OC\Files\View('/'));
				$user = \OC::$server->getUserSession()->getUser();
				$this->userId = $user ? $user->getUID() : Helper::getUserFromPath($this->rawPath);
				break;
			default:
				\OCP\Util::writeLog('Encryption library', 'failed to open file "' . $this->rawPath . '" expecting a path to "files", "files_versions" or "cache"', \OCP\Util::ERROR);
				return false;
		}

		// Disable fileproxies so we can get the file size and open the source file without recursive encryption
		$proxyStatus = \OC_FileProxy::$enabled;
		\OC_FileProxy::$enabled = false;

		$this->position = 0;
		$this->cache = '';
		$this->writeFlag = 0;

		// Setting handle so it can be used for reading the header
		if ($this->isLocalTmpFile) {
			$this->handle = fopen($this->localTmpFile, $mode);
		} else {
			$this->handle = $this->rootView->fopen($this->rawPath, $mode);
		}

		if (
			$mode === 'w'
			or $mode === 'w+'
			or $mode === 'wb'
			or $mode === 'wb+'
		) {
			// We're writing a new file so start write counter with 0 bytes
			$this->size = 0;
			$this->unencryptedSize = 0;
		} else {
			$this->size = $this->rootView->filesize($this->rawPath);
			\OC_FileProxy::$enabled = true;
			$this->unencryptedSize = $this->rootView->filesize($this->rawPath);
			\OC_FileProxy::$enabled = false;
			$this->readHeader();
		}

		\OC_FileProxy::$enabled = $proxyStatus;

		if (!is_resource($this->handle)) {

			\OCP\Util::writeLog('Encryption library', 'failed to open file "' . $this->rawPath . '"', \OCP\Util::ERROR);

		} else {

			$this->meta = stream_get_meta_data($this->handle);
			// sometimes fopen changes the mode, e.g. for a url "r" convert to "r+"
			// but we need to remember the original access type
			$this->meta['mode'] = $mode;

		}


		return is_resource($this->handle);

	}

	private function readHeader() {

		if (is_resource($this->handle)) {
			$data = fread($this->handle, Crypt::BLOCKSIZE);

			$header = Crypt::parseHeader($data);
			$this->cipher = Crypt::getCipher($header);

			// remeber that we found a header
			if (!empty($header)) {
				$this->containHeader = true;
				$this->headerSize = Crypt::BLOCKSIZE;
			// if there's no header then decrypt the block and store it in the cache
			} else {
				if (!$this->getKey()) {
					throw new \Exception('Encryption key not found for "' . $this->rawPath . '" during attempted read via stream');
				} else {
					$this->cache = Crypt::symmetricDecryptFileContent($data, $this->plainKey, $this->cipher);
				}
			}

		}
	}

	/**
	 * Returns the current position of the file pointer
	 * @return int position of the file pointer
	 */
	public function stream_tell() {
		return $this->position;
	}

	/**
	 * @param int $offset
	 * @param int $whence
	 * @return bool true if fseek was successful, otherwise false
	 */

	// seeking the stream tries to move the pointer on the encrypted stream to the beginning of the target block
	// if that works, it flushes the current block and changes the position in the unencrypted stream
	public function stream_seek($offset, $whence = SEEK_SET) {
		// this wrapper needs to return "true" for success.
		// the fseek call itself returns 0 on succeess

		$return=false;

		switch($whence) {
			case SEEK_SET:
				if($offset < $this->unencryptedSize && $offset >= 0) {
					$newPosition=$offset;
				}
				break;
			case SEEK_CUR:
				if($offset>=0) {
					$newPosition=$offset+$this->position;
				}
				break;
			case SEEK_END:
				if($this->unencryptedSize + $offset >= 0) {
					$newPosition=$this->unencryptedSize+$offset;
				}
				break;
			default:
				return $return;
		}
		$newFilePosition=floor($newPosition/6126)*Crypt::BLOCKSIZE+$this->headerSize;
		if (fseek($this->handle, $newFilePosition)===0) {
			$this->flush();
			$this->position=$newPosition;
			$return=true;
		}
		return $return;

	}

	/**
	 * @param int $count
	 * @return bool|string
	 * @throws \OCA\Files_Encryption\Exception\EncryptionException
	 */
	public function stream_read($count) {

		$result = '';

		// limit to the end of the unencrypted file; otherwise getFileSize will fail and it is good practise anyway
		$count=min($count,$this->unencryptedSize - $this->position);

		// loop over the 6126 sized unencrypted blocks
		while ($count > 0) {

			$remainingLength = $count;

			// update the cache of the current block
			$this->readCache();
			
			// determine the relative position in the current block
			$blockPosition=($this->position % 6126);

			// if entire read inside current block then only position needs to be updated
			if ($remainingLength<(6126 - $blockPosition)) {
				$result .= substr($this->cache,$blockPosition,$remainingLength);
				$this->position += $remainingLength;
				$count=0;
			// otherwise remainder of current block is fetched, the block is flushed and the position updated
			} else {
				$result .= substr($this->cache,$blockPosition);
				$this->flush();
				$this->position += (6126 - $blockPosition);
				$count -= (6126 - $blockPosition);
			}

		}

		return $result;

	}

	/**
	 * Encrypt and pad data ready for writing to disk
	 * @param string $plainData data to be encrypted
	 * @param string $key key to use for encryption
	 * @return string encrypted data on success, false on failure
	 */
	public function preWriteEncrypt($plainData, $key) {

		// Encrypt data to 'catfile', which includes IV
		if ($encrypted = Crypt::symmetricEncryptFileContent($plainData, $key, $this->cipher)) {

			return $encrypted;

		} else {

			return false;

		}

	}

	/**
	 * Fetch the plain encryption key for the file and set it as plainKey property
	 * @internal param bool $generate if true, a new key will be generated if none can be found
	 * @return bool true on key found and set, false on key not found and new key generated and set
	 */
	public function getKey() {

		// Check if key is already set
		if (isset($this->plainKey) && isset($this->encKeyfile)) {

			return true;

		}

		// Fetch and decrypt keyfile
		// Fetch existing keyfile
		$this->encKeyfile = Keymanager::getFileKey($this->rootView, $this->util, $this->relPath);

		// If a keyfile already exists
		if ($this->encKeyfile) {

			$shareKey = Keymanager::getShareKey($this->rootView, $this->keyId, $this->util, $this->relPath);

			// if there is no valid private key return false
			if ($this->privateKey === false) {
				// if private key is not valid redirect user to a error page
				Helper::redirectToErrorPage($this->session);
				return false;
			}

			if ($shareKey === false) {
				// if no share key is available redirect user to a error page
				Helper::redirectToErrorPage($this->session, Crypt::ENCRYPTION_NO_SHARE_KEY_FOUND);
				return false;
			}

			$this->plainKey = Crypt::multiKeyDecrypt($this->encKeyfile, $shareKey, $this->privateKey);

			return true;

		} else {

			$this->newFile = true;

			return false;

		}

	}

	/**
	 * write header at beginning of encrypted file
	 *
	 * @throws \OCA\Files_Encryption\Exception\EncryptionException
	 */
	private function writeHeader() {

		$header = Crypt::generateHeader();

		if (strlen($header) > Crypt::BLOCKSIZE) {
			throw new EncryptionException('max header size exceeded', EncryptionException::ENCRYPTION_HEADER_TO_LARGE);
		}

		$paddedHeader = str_pad($header, Crypt::BLOCKSIZE, self::PADDING_CHAR, STR_PAD_RIGHT);

		fwrite($this->handle, $paddedHeader);
		$this->headerWritten = true;
		$this->containHeader = true;
		$this->headerSize = Crypt::BLOCKSIZE;
		$this->size += $this->headerSize;
	}

	/**
	 * Handle plain data from the stream, and write it in 8192 byte blocks
	 * @param string $data data to be written to disk
	 * @note the data will be written to the path stored in the stream handle, set in stream_open()
	 * @note $data is only ever be a maximum of 8192 bytes long. This is set by PHP internally. stream_write() is called multiple times in a loop on data larger than 8192 bytes
	 * @note Because the encryption process used increases the length of $data, a cache is used to carry over data which would not fit in the required block size
	 * @note Padding is added to each encrypted block to ensure that the resulting block is exactly 8192 bytes. This is removed during stream_read
	 * @note PHP automatically updates the file pointer after writing data to reflect it's length. There is generally no need to update the poitner manually using fseek
	 */
	public function stream_write($data) {

		// if there is no valid private key return false
		if ($this->privateKey === false) {
			$this->size = 0;
			return strlen($data);
		}

		if ($this->size === 0) {
			$this->writeHeader();
		}

		// Get / generate the keyfile for the file we're handling
		// If we're writing a new file (not overwriting an existing
		// one), save the newly generated keyfile
		if (!$this->getKey()) {

			$this->plainKey = Crypt::generateKey();

		}

		$length=0;

		// loop over $data to fit it in 6126 sized unencrypted blocks
		while (strlen($data) > 0) {

			$remainingLength = strlen($data);

			// set the cache to the current 6126 block
			$this->readCache();

			// only allow writes on seekable streams, or at the end of the encrypted stream
			// for seekable streams the pointer is moved back to the beginning of the encrypted block
			// flush will start writing there when the position moves to another block
			if((fseek($this->handle, floor($this->position/6126)*Crypt::BLOCKSIZE + $this->headerSize) === 0) || (floor($this->position/6126)*Crypt::BLOCKSIZE + $this->headerSize === $this->size)) {

				// switch the writeFlag so flush() will write the block
				$this->writeFlag=1;
				
				// determine the relative position in the current block
				$blockPosition=($this->position % 6126);

				// check if $data fits in current block
				// if so, overwrite existing data (if any)
				// update position and liberate $data
				if ($remainingLength<(6126 - $blockPosition)) {
					$this->cache=substr($this->cache,0,$blockPosition).$data.substr($this->cache,$blockPosition+$remainingLength);
					$this->position += $remainingLength;
					$length += $remainingLength;
					$data = '';
				// if $data doens't fit the current block, the fill the current block and reiterate
				// after the block is filled, it is flushed and $data is updated
				} else {
					$this->cache=substr($this->cache,0,$blockPosition).substr($data,0,6126-$blockPosition);
					$this->flush();
					$this->position += (6126 - $blockPosition);
					$length += (6126 - $blockPosition);
					$data = substr($data, 6126 - $blockPosition);
				}

			} else {
				$data='';
			}
		}

		$this->unencryptedSize = max($this->unencryptedSize,$this->position);

		return $length;

	}


	/**
	 * @param int $option
	 * @param int $arg1
	 * @param int|null $arg2
	 */
	public function stream_set_option($option, $arg1, $arg2) {
		$return = false;
		switch ($option) {
			case STREAM_OPTION_BLOCKING:
				$return = stream_set_blocking($this->handle, $arg1);
				break;
			case STREAM_OPTION_READ_TIMEOUT:
				$return = stream_set_timeout($this->handle, $arg1, $arg2);
				break;
			case STREAM_OPTION_WRITE_BUFFER:
				$return = stream_set_write_buffer($this->handle, $arg1);
		}

		return $return;
	}

	/**
	 * @return array
	 */
	public function stream_stat() {
		return fstat($this->handle);
	}

	/**
	 * @param int $mode
	 */
	public function stream_lock($mode) {
		return flock($this->handle, $mode);
	}

	/**
	 * @return bool
	 */
	public function stream_flush() {

		$this->flush();
		return fflush($this->handle);
		// Not a typo: http://php.net/manual/en/function.fflush.php

	}

	/**
	 * @return bool
	 */
	public function stream_eof() {
		return ($this->position>=$this->unencryptedSize);
	}

	private function flush() {

		// write to disk only when writeFlag was set to 1
		if ($this->writeFlag === 1) {
			// Disable the file proxies so that encryption is not
			// automatically attempted when the file is written to disk -
			// we are handling that separately here and we don't want to
			// get into an infinite loop
			$proxyStatus = \OC_FileProxy::$enabled;
			\OC_FileProxy::$enabled = false;
			// Set keyfile property for file in question
			$this->getKey();
			$encrypted = $this->preWriteEncrypt($this->cache, $this->plainKey);
			fwrite($this->handle, $encrypted);
			$this->writeFlag = 0;
			$this->size = max($this->size,ftell($this->handle));
			\OC_FileProxy::$enabled = $proxyStatus;
		}
		// always empty the cache (otherwise readCache() will not fill it with the new block)
		$this->cache = '';
	}

	private function readCache() {
		// cache should always be empty string when this function is called
		// don't try to fill the cache when trying to write at the end of the unencrypted file when it coincides with new block
		if ($this->cache === '' && !($this->position===$this->unencryptedSize && ($this->position % 6126)===0)) {
			// Get the data from the file handle
			$data = fread($this->handle, Crypt::BLOCKSIZE);
			$result = '';
			if (strlen($data)) {
				if (!$this->getKey()) {
					// Error! We don't have a key to decrypt the file with
					throw new \Exception('Encryption key not found for "'. $this->rawPath . '" during attempted read via stream');
				} else {
					// Decrypt data
					$result = Crypt::symmetricDecryptFileContent($data, $this->plainKey, $this->cipher);
				}
			}
			$this->cache = $result;
		}
	}

	/**
	 * @return bool
	 */
	public function stream_close() {

		$this->flush();

		// if there is no valid private key return false
		if ($this->privateKey === false) {

			// cleanup
			if ($this->meta['mode'] !== 'r' && $this->meta['mode'] !== 'rb' && !$this->isLocalTmpFile) {

				// Disable encryption proxy to prevent recursive calls
				$proxyStatus = \OC_FileProxy::$enabled;
				\OC_FileProxy::$enabled = false;

				if ($this->rootView->file_exists($this->rawPath) && $this->size === $this->headerSize) {
					fclose($this->handle);
					$this->rootView->unlink($this->rawPath);
				}

				// Re-enable proxy - our work is done
				\OC_FileProxy::$enabled = $proxyStatus;
			}

			// if private key is not valid redirect user to a error page
			Helper::redirectToErrorPage($this->session);
		}

		if (
				$this->meta['mode'] !== 'r' &&
				$this->meta['mode'] !== 'rb' &&
				$this->isLocalTmpFile === false &&
				$this->size > $this->headerSize &&
				$this->unencryptedSize > 0
		) {

			// only write keyfiles if it was a new file
			if ($this->newFile === true) {

				// Disable encryption proxy to prevent recursive calls
				$proxyStatus = \OC_FileProxy::$enabled;
				\OC_FileProxy::$enabled = false;

				// Fetch user's public key
				$this->publicKey = Keymanager::getPublicKey($this->rootView, $this->keyId);

				// Check if OC sharing api is enabled
				$sharingEnabled = \OCP\Share::isEnabled();

				// Get all users sharing the file includes current user
				$uniqueUserIds = $this->util->getSharingUsersArray($sharingEnabled, $this->relPath);
				$checkedUserIds = $this->util->filterShareReadyUsers($uniqueUserIds);

				// Fetch public keys for all sharing users
				$publicKeys = Keymanager::getPublicKeys($this->rootView, $checkedUserIds['ready']);

				// Encrypt enc key for all sharing users
				$this->encKeyfiles = Crypt::multiKeyEncrypt($this->plainKey, $publicKeys);

				// Save the new encrypted file key
				Keymanager::setFileKey($this->rootView, $this->util, $this->relPath, $this->encKeyfiles['data']);

				// Save the sharekeys
				Keymanager::setShareKeys($this->rootView, $this->util, $this->relPath, $this->encKeyfiles['keys']);

				// Re-enable proxy - our work is done
				\OC_FileProxy::$enabled = $proxyStatus;
			}

			// we need to update the file info for the real file, not for the
			// part file.
			$path = Helper::stripPartialFileExtension($this->rawPath);

			$fileInfo = array(
				'mimetype' => $this->rootView->getMimeType($this->rawPath),
				'encrypted' => true,
				'unencrypted_size' => $this->unencryptedSize,
			);

			// if we write a part file we also store the unencrypted size for
			// the part file so that it can be re-used later
			$this->rootView->putFileInfo($this->rawPath, $fileInfo);
			if ($path !== $this->rawPath) {
				$this->rootView->putFileInfo($path, $fileInfo);
			}

		}

		$result = fclose($this->handle);

		if ($result === false) {
			\OCP\Util::writeLog('Encryption library', 'Could not close stream, file could be corrupted', \OCP\Util::FATAL);
		}

		return $result;

	}

}