linux-kernel - Re: [PATCH v7 7/8] ext4: Hande casefolding with encryption

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Date:   Tue, 11 Feb 2020 21:59:09 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Daniel Rosenberg <drosen@...gle.com>
Cc:     Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fscrypt@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Richard Weinberger <richard@....at>,
        linux-mtd@...ts.infradead.org,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        kernel-team@...roid.com
Subject: Re: [PATCH v7 7/8] ext4: Hande casefolding with encryption

On Fri, Feb 07, 2020 at 05:35:51PM -0800, Daniel Rosenberg wrote:
> This adds support for encryption with casefolding.
> 
> Since the name on disk is case preserving, and also encrypted, we can no
> longer just recompute the hash on the fly. Additionally, to avoid
> leaking extra information from the hash of the unencrypted name, we use
> siphash via an fscrypt v2 policy.
> 
> The hash is stored at the end of the directory entry for all entries
> inside of an encrypted and casefolded directory apart from those that
> deal with '.' and '..'. This way, the change is backwards compatible
> with existing ext4 filesystems.
> 
> Signed-off-by: Daniel Rosenberg <drosen@...gle.com>
> ---
>  Documentation/filesystems/ext4/directory.rst |  27 ++
>  fs/ext4/dir.c                                |  27 +-
>  fs/ext4/ext4.h                               |  64 +++-
>  fs/ext4/hash.c                               |  24 +-
>  fs/ext4/ialloc.c                             |   5 +-
>  fs/ext4/inline.c                             |  41 +--
>  fs/ext4/namei.c                              | 291 +++++++++++++------
>  fs/ext4/super.c                              |   6 -
>  8 files changed, 343 insertions(+), 142 deletions(-)

How was this tested?  I tried it (using a patched version of 'mke2fs' that
allows the encrypt and encoding options to be combined), and I immediately got
an ext4 error about a bad directory entry:

~/e2fsprogs/misc/mke2fs -F -t ext4 -O encrypt -E encoding=utf8 /dev/vdb
mount /dev/vdb /mnt
fscrypt setup /mnt
mkdir /mnt/dir
# (assumes /etc/fscrypt.conf contains policy_version 2)
echo hunter2 | fscrypt encrypt /mnt/dir --quiet --source=custom_passphrase --name=dir
chattr +F /mnt/dir
echo contents > /mnt/dir/file
umount /mnt
mount /dev/vdb /mnt
ls /mnt/dir/
[  391.292067] EXT4-fs error (device vdb): htree_dirblock_to_tree:1038: inode #8193: block 4251: comm ls: bad entry in directory: directory entry too close to block end - offset=80, inode=18, rec_len=4004, lblk=0, size=4096