On 01/15, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> Add support for FS_VERITY_METADATA_TYPE_DESCRIPTOR to
> FS_IOC_READ_VERITY_METADATA. This allows a userspace server program to
> retrieve the fs-verity descriptor of a file for serving to a client
> which implements fs-verity compatible verification. See the patch which
> introduced FS_IOC_READ_VERITY_METADATA for more details.
>
> "fs-verity descriptor" here means only the part that userspace cares
> about because it is hashed to produce the file digest. It doesn't
> include the signature which ext4 and f2fs append to the
> fsverity_descriptor struct when storing it on-disk, since that way of
> storing the signature is an implementation detail. The next patch adds
> a separate metadata_type value for retrieving the signature separately.
>
> This has been tested using a new xfstest which calls this ioctl via a
> new subcommand for the 'fsverity' program from fsverity-utils.
>
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Reviewed-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> ---
> Documentation/filesystems/fsverity.rst | 4 +++
> fs/verity/read_metadata.c | 40 ++++++++++++++++++++++++++
> include/uapi/linux/fsverity.h | 1 +
> 3 files changed, 45 insertions(+)
>
> diff --git a/Documentation/filesystems/fsverity.rst b/Documentation/filesystems/fsverity.rst
> index 50b47a6d9ea11..6dc5772037ef9 100644
> --- a/Documentation/filesystems/fsverity.rst
> +++ b/Documentation/filesystems/fsverity.rst
> @@ -235,6 +235,7 @@ need this ioctl.
> This ioctl takes in a pointer to the following structure::
>
> #define FS_VERITY_METADATA_TYPE_MERKLE_TREE 1
> + #define FS_VERITY_METADATA_TYPE_DESCRIPTOR 2
>
> struct fsverity_read_metadata_arg {
> __u64 metadata_type;
> @@ -252,6 +253,9 @@ This ioctl takes in a pointer to the following structure::
> the same order that their hashes are themselves hashed.
> See `Merkle tree`_ for more information.
>
> +- ``FS_VERITY_METADATA_TYPE_DESCRIPTOR`` reads the fs-verity
> + descriptor. See `fs-verity descriptor`_.
> +
> The semantics are similar to those of ``pread()``. ``offset``
> specifies the offset in bytes into the metadata item to read from, and
> ``length`` specifies the maximum number of bytes to read from the
> diff --git a/fs/verity/read_metadata.c b/fs/verity/read_metadata.c
> index 0f8ad2991cf90..2dea6dd3bb05a 100644
> --- a/fs/verity/read_metadata.c
> +++ b/fs/verity/read_metadata.c
> @@ -76,6 +76,44 @@ static int fsverity_read_merkle_tree(struct inode *inode,
> }
> return retval ? retval : err;
> }
> +
> +/* Copy the requested portion of the buffer to userspace. */
> +static int fsverity_read_buffer(void __user *dst, u64 offset, int length,
> + const void *src, size_t src_length)
> +{
> + if (offset >= src_length)
> + return 0;
> + src += offset;
> + src_length -= offset;
> +
> + length = min_t(size_t, length, src_length);
> +
> + if (copy_to_user(dst, src, length))
> + return -EFAULT;
> +
> + return length;
> +}
> +
> +static int fsverity_read_descriptor(struct inode *inode,
> + void __user *buf, u64 offset, int length)
> +{
> + struct fsverity_descriptor *desc;
> + size_t desc_size;
> + int res;
> +
> + res = fsverity_get_descriptor(inode, &desc, &desc_size);
> + if (res)
> + return res;
> +
> + /* don't include the signature */
> + desc_size = offsetof(struct fsverity_descriptor, signature);
> + desc->sig_size = 0;
> +
> + res = fsverity_read_buffer(buf, offset, length, desc, desc_size);
> +
> + kfree(desc);
> + return res;
> +}
> /**
> * fsverity_ioctl_read_metadata() - read verity metadata from a file
> * @filp: file to read the metadata from
> @@ -118,6 +156,8 @@ int fsverity_ioctl_read_metadata(struct file *filp, const void __user *uarg)
> case FS_VERITY_METADATA_TYPE_MERKLE_TREE:
> return fsverity_read_merkle_tree(inode, vi, buf, arg.offset,
> length);
> + case FS_VERITY_METADATA_TYPE_DESCRIPTOR:
> + return fsverity_read_descriptor(inode, buf, arg.offset, length);
> default:
> return -EINVAL;
> }
> diff --git a/include/uapi/linux/fsverity.h b/include/uapi/linux/fsverity.h
> index 94003b153cb3d..41abc283dbccb 100644
> --- a/include/uapi/linux/fsverity.h
> +++ b/include/uapi/linux/fsverity.h
> @@ -84,6 +84,7 @@ struct fsverity_formatted_digest {
> };
>
> #define FS_VERITY_METADATA_TYPE_MERKLE_TREE 1
> +#define FS_VERITY_METADATA_TYPE_DESCRIPTOR 2
>
> struct fsverity_read_metadata_arg {
> __u64 metadata_type;
> --
> 2.30.0
