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

Eric Biggers
2020-02-12T05:59:13Z

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@google.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