linux-ext4 - Re: [f2fs-dev] [PATCH v6 17/17] f2fs: add fs-verity support

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Date:   Wed, 3 Jul 2019 09:25:44 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Eric Biggers <ebiggers@...nel.org>, <linux-fscrypt@...r.kernel.org>
CC:     "Theodore Y . Ts'o" <tytso@....edu>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        <linux-api@...r.kernel.org>, Dave Chinner <david@...morbit.com>,
        <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-fsdevel@...r.kernel.org>, Jaegeuk Kim <jaegeuk@...nel.org>,
        <linux-integrity@...r.kernel.org>, <linux-ext4@...r.kernel.org>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Victor Hsieh <victorhsieh@...gle.com>
Subject: Re: [f2fs-dev] [PATCH v6 17/17] f2fs: add fs-verity support

On 2019/7/1 23:32, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> Add fs-verity support to f2fs.  fs-verity is a filesystem feature that
> enables transparent integrity protection and authentication of read-only
> files.  It uses a dm-verity like mechanism at the file level: a Merkle
> tree is used to verify any block in the file in log(filesize) time.  It
> is implemented mainly by helper functions in fs/verity/.  See
> Documentation/filesystems/fsverity.rst for the full documentation.
> 
> The f2fs support for fs-verity consists of:
> 
> - Adding a filesystem feature flag and an inode flag for fs-verity.
> 
> - Implementing the fsverity_operations to support enabling verity on an
>   inode and reading/writing the verity metadata.
> 
> - Updating ->readpages() to verify data as it's read from verity files
>   and to support reading verity metadata pages.
> 
> - Updating ->write_begin(), ->write_end(), and ->writepages() to support
>   writing verity metadata pages.
> 
> - Calling the fs-verity hooks for ->open(), ->setattr(), and ->ioctl().
> 
> Like ext4, f2fs stores the verity metadata (Merkle tree and
> fsverity_descriptor) past the end of the file, starting at the first 64K
> boundary beyond i_size.  This approach works because (a) verity files
> are readonly, and (b) pages fully beyond i_size aren't visible to
> userspace but can be read/written internally by f2fs with only some
> relatively small changes to f2fs.  Extended attributes cannot be used
> because (a) f2fs limits the total size of an inode's xattr entries to
> 4096 bytes, which wouldn't be enough for even a single Merkle tree
> block, and (b) f2fs encryption doesn't encrypt xattrs, yet the verity
> metadata *must* be encrypted when the file is because it contains hashes
> of the plaintext data.
> 
> Acked-by: Jaegeuk Kim <jaegeuk@...nel.org>
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Acked-by: Chao Yu <yuchao0@...wei.com>

Thanks,