From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Biggers Subject: Re: [PATCH 1/3] ext4: require key for truncate(2) of encrypted file Date: Wed, 14 Jun 2017 00:03:57 -0700 Message-ID: <20170614070357.GB605@zzz> References: <20170613234755.111167-1-ebiggers3@gmail.com> <20170613234755.111167-2-ebiggers3@gmail.com> <20170614065210.GA10411@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20170614065210.GA10411@infradead.org> Sender: linux-fsdevel-owner@vger.kernel.org To: Christoph Hellwig Cc: linux-fscrypt@vger.kernel.org, Theodore Ts'o , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mtd@lists.infradead.org, Eric Biggers List-Id: linux-f2fs-devel.lists.sourceforge.net Hi Christoph, On Tue, Jun 13, 2017 at 11:52:10PM -0700, Christoph Hellwig wrote: > On Tue, Jun 13, 2017 at 04:47:53PM -0700, Eric Biggers wrote: > > From: Eric Biggers > > > > Currently, filesystems allow truncate(2) on an encrypted file without > > the encryption key. However, it's impossible to correctly handle the > > case where the size being truncated to is not a multiple of the > > filesystem block size, because that would require decrypting the final > > block, zeroing the part beyond i_size, then encrypting the block. > > > > As other modifications to encrypted file contents are prohibited without > > the key, just prohibit truncate(2) as well, making it fail with ENOKEY. > > What about hole punches? What about fallocate which just adds zeroes > but still changes the content. What about insert or collapse range? None of those are allowed because fallocate() requires a file descriptor, and open() fails with ENOKEY if the encryption key is not available. truncate() is different because it takes a path, not a file descriptor. Eric