linux-kernel - Re: [PATCH 0/3] add support for metadata encryption to F2FS

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Message-ID: <20201005074356.GA1961565@google.com>
Date:   Mon, 5 Oct 2020 07:43:56 +0000
From:   Satya Tangirala <satyat@...gle.com>
To:     "Theodore Y . Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Eric Biggers <ebiggers@...nel.org>, Chao Yu <chao@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-fscrypt@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH 0/3] add support for metadata encryption to F2FS

On Mon, Oct 05, 2020 at 07:36:03AM +0000, Satya Tangirala wrote:
> This patch series adds support for metadata encryption to F2FS using
> blk-crypto.
> 
> Patch 1 replaces fscrypt_get_devices (which took an array of request_queues
> and filled it up) with fscrypt_get_device, which takes a index of the
> desired device and returns the device at that index (so the index passed
> to fscrypt_get_device must be between 0 and (fscrypt_get_num_devices() - 1)
> inclusive). This allows callers to avoid having to allocate an array to
> pass to fscrypt_get_devices() when they only need to iterate through
> each element in the array (and have no use for the array itself).
> 
> Patch 2 introduces some functions to fscrypt that help filesystems perform
> metadata encryption. Any filesystem that wants to use metadata encryption
> can call fscrypt_setup_metadata_encryption() with the super_block of the
> filesystem, the encryption algorithm and the descriptor of the encryption
> key. The descriptor is looked up in the logon keyring of the current
> session with "fscrypt:" as the prefix of the descriptor.
> 
> The patch also introduces fscrypt_metadata_crypt_bio() which an FS should
> call on a bio that the FS wants metadata crypted. The function will add
> an encryption context with the metadata encryption key set up by the call
> to the above mentioned fscrypt_setup_metadata_encryption().
> 
> The patch also introduces fscrypt_metadata_crypt_prepare_all_devices().
> Filesystems that use multiple devices should call this function once all
> the underlying devices have been determined. An FS might only be able to
> determine all the underlying devices after some initial processing that
> might already require metadata en/decryption, which is why this function
> is separate from fscrypt_setup_metadata_encryption().
> 
> Patch 3 wires up F2FS with the functions introduced in Patch 2. F2FS
> will encrypt every block (that's not being encrypted by some other
> encryption key, e.g. a per-file key) with the metadata encryption key
> except the superblock (and the redundant copy of the superblock). The DUN
> of a block is the offset of the block from the start of the F2FS
> filesystem.
> 
> Please refer to the commit message for why the superblock was excluded from
> en/decryption, and other limitations. The superblock and its copy are
> stored in plaintext on disk. The encryption algorithm used for metadata
> encryption is stored within the superblock itself. Changes to the userspace
> tools (that are required to test out metadata encryption with F2FS) are
> also being sent out - I'll post a link as a reply to this mail once it's
> out.
The userspace patches are at

https://lore.kernel.org/linux-fscrypt/20201005074133.1958633-2-satyat@google.com/

> 
> Satya Tangirala (3):
>   fscrypt, f2fs: replace fscrypt_get_devices with fscrypt_get_device
>   fscrypt: Add metadata encryption support
>   f2fs: Add metadata encryption support
> 
>  Documentation/filesystems/f2fs.rst |  12 ++
>  fs/crypto/Kconfig                  |   6 +
>  fs/crypto/Makefile                 |   1 +
>  fs/crypto/fscrypt_private.h        |  19 +++
>  fs/crypto/inline_crypt.c           |  37 +----
>  fs/crypto/metadata_crypt.c         | 220 +++++++++++++++++++++++++++++
>  fs/f2fs/data.c                     |  24 ++--
>  fs/f2fs/f2fs.h                     |   2 +
>  fs/f2fs/super.c                    |  83 +++++++++--
>  include/linux/f2fs_fs.h            |   3 +-
>  include/linux/fs.h                 |   3 +
>  include/linux/fscrypt.h            |  51 ++++++-
>  12 files changed, 410 insertions(+), 51 deletions(-)
>  create mode 100644 fs/crypto/metadata_crypt.c
> 
> -- 
> 2.28.0.806.g8561365e88-goog
>