From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Biggers Subject: A few more filesystem encryption questions Date: Sun, 3 Apr 2016 00:58:33 -0500 Message-ID: <20160403055833.GA3214@zzz> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: tytso@mit.edu, mhalcrow@google.com, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, jaegeuk@kernel.org, linux-ext4@vger.kernel.org To: linux-fsdevel@vger.kernel.org Return-path: Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net List-Id: linux-ext4.vger.kernel.org Hello, A few more questions about the new filesystem encryption code: I found that a process without access to the master encryption key can read a file's full decrypted contents, provided that the file was opened recently by a process with access to the key. This is true even if the privileged process merely opened and closed the file, without reading any bytes. A similar story applies to filenames; a 'ls' by a process able to decrypt the names reveals them to all users/processes. Essentially, it seems that despite the use of the kernel keyrings mechanism where different users/processes can have different keys, this doesn't fully carry over into filesystem encryption. Is this a known and understood limitation of the design? The design document states that an encryption policy can be changed "if the directory is empty or the file is 0 bytes in length". However, the code doesn't allow an existing encryption policy to be changed. Which behavior was intended? I had brought up the question of the endianness of the XTS tweak value. I also realized that since the page index is used, the XTS tweak will be dependent on PAGE_SIZE. So the current behavior is that an encrypted filesystem can only be read on a device with the same endianness _and_ PAGE_SIZE. Is is the case that due to the early Android users, it is too late to start using the byte offset instead of the PAGE_SIZE? What about if the XTS tweak was fixed as the number of 4096-byte blocks from the start of the file as a le64 --- is that what the existing users are expected to be doing in practice? Are there any architectures with PAGE_SIZE < 4096 for which that value wouldn't work? Eric ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. Click to learn more. http://pubads.g.doubleclick.net/gampad/clk?id=278785471&iu=/4140