linux-ext4 - Re: [PATCH 1/3] ext4: require key for truncate(2) of encrypted file

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Message-ID: <20170623235254.l5wyukjiy2mdms3m@thunk.org>
Date:   Fri, 23 Jun 2017 19:52:54 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-mtd@...ts.infradead.org, Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH 1/3] ext4: require key for truncate(2) of encrypted file

On Tue, Jun 13, 2017 at 04:47:53PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> 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.
> 
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Thanks, applied.

					- Ted