• Eric Biggers's avatar
    f2fs: add fs-verity support · 95ae251f
    Eric Biggers authored
    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: default avatarJaegeuk Kim <jaegeuk@kernel.org>
    Acked-by: default avatarChao Yu <yuchao0@huawei.com>
    Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
    95ae251f
verity.c 6.55 KB