linux-ext4 - Re: [PATCH v6 14/17] ext4: add basic fs-verity support

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Date:   Sun, 7 Jul 2019 14:51:17 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-integrity@...r.kernel.org, Jaegeuk Kim <jaegeuk@...nel.org>,
        Victor Hsieh <victorhsieh@...gle.com>,
        Chandan Rajendra <chandan@...ux.vnet.ibm.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v6 14/17] ext4: add basic fs-verity support

On Mon, Jul 01, 2019 at 08:32:34AM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> Add most of fs-verity support to ext4.  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.
> 
> This commit adds all of ext4 fs-verity support except for the actual
> data verification, including:
> 
> - 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 ->write_begin(), ->write_end(), and ->writepages() to support
>   writing verity metadata pages.
> 
> - Calling the fs-verity hooks for ->open(), ->setattr(), and ->ioctl().
> 
> ext4 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 ext4 with only some relatively small changes
> to ext4.  This approach avoids having to depend on the EA_INODE feature
> and on rearchitecturing ext4's xattr support to support paging
> multi-gigabyte xattrs into memory, and to support encrypting xattrs.
> Note that the verity metadata *must* be encrypted when the file is,
> since it contains hashes of the plaintext data.
> 
> This patch incorporates work by Theodore Ts'o and Chandan Rajendra.
> 
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Looks good.  You can add:

Reviewed-by: Theodore Ts'o <tytso@....edu>

Thanks,

					- Ted