On 01/15, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> Add support for FS_VERITY_METADATA_TYPE_SIGNATURE to
> FS_IOC_READ_VERITY_METADATA. This allows a userspace server program to
> retrieve the built-in signature (if present) of a verity 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.
>
> The ability for userspace to read the built-in signatures is also useful
> because it allows a system that is using the in-kernel signature
> verification to migrate to userspace signature verification.
>
> 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 | 9 +++++++-
> fs/verity/read_metadata.c | 30 ++++++++++++++++++++++++++
> include/uapi/linux/fsverity.h | 1 +
> 3 files changed, 39 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/filesystems/fsverity.rst b/Documentation/filesystems/fsverity.rst
> index 6dc5772037ef9..1d831e3cbcb33 100644
> --- a/Documentation/filesystems/fsverity.rst
> +++ b/Documentation/filesystems/fsverity.rst
> @@ -236,6 +236,7 @@ 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
> + #define FS_VERITY_METADATA_TYPE_SIGNATURE 3
>
> struct fsverity_read_metadata_arg {
> __u64 metadata_type;
> @@ -256,6 +257,10 @@ This ioctl takes in a pointer to the following structure::
> - ``FS_VERITY_METADATA_TYPE_DESCRIPTOR`` reads the fs-verity
> descriptor. See `fs-verity descriptor`_.
>
> +- ``FS_VERITY_METADATA_TYPE_SIGNATURE`` reads the signature which was
> + passed to FS_IOC_ENABLE_VERITY, if any. See `Built-in signature
> + verification`_.
> +
> 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
> @@ -279,7 +284,9 @@ FS_IOC_READ_VERITY_METADATA can fail with the following errors:
> - ``EINTR``: the ioctl was interrupted before any data was read
> - ``EINVAL``: reserved fields were set, or ``offset + length``
> overflowed
> -- ``ENODATA``: the file is not a verity file
> +- ``ENODATA``: the file is not a verity file, or
> + FS_VERITY_METADATA_TYPE_SIGNATURE was requested but the file doesn't
> + have a built-in signature
> - ``ENOTTY``: this type of filesystem does not implement fs-verity, or
> this ioctl is not yet implemented on it
> - ``EOPNOTSUPP``: the kernel was not configured with fs-verity
> diff --git a/fs/verity/read_metadata.c b/fs/verity/read_metadata.c
> index 2dea6dd3bb05a..7e2d0c7bdf0de 100644
> --- a/fs/verity/read_metadata.c
> +++ b/fs/verity/read_metadata.c
> @@ -114,6 +114,34 @@ static int fsverity_read_descriptor(struct inode *inode,
> kfree(desc);
> return res;
> }
> +
> +static int fsverity_read_signature(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;
> +
> + if (desc->sig_size == 0) {
> + res = -ENODATA;
> + goto out;
> + }
> +
> + /*
> + * Include only the signature. Note that fsverity_get_descriptor()
> + * already verified that sig_size is in-bounds.
> + */
> + res = fsverity_read_buffer(buf, offset, length, desc->signature,
> + le32_to_cpu(desc->sig_size));
> +out:
> + kfree(desc);
> + return res;
> +}
> +
> /**
> * fsverity_ioctl_read_metadata() - read verity metadata from a file
> * @filp: file to read the metadata from
> @@ -158,6 +186,8 @@ int fsverity_ioctl_read_metadata(struct file *filp, const void __user *uarg)
> length);
> case FS_VERITY_METADATA_TYPE_DESCRIPTOR:
> return fsverity_read_descriptor(inode, buf, arg.offset, length);
> + case FS_VERITY_METADATA_TYPE_SIGNATURE:
> + return fsverity_read_signature(inode, buf, arg.offset, length);
> default:
> return -EINVAL;
> }
> diff --git a/include/uapi/linux/fsverity.h b/include/uapi/linux/fsverity.h
> index 41abc283dbccb..15384e22e331e 100644
> --- a/include/uapi/linux/fsverity.h
> +++ b/include/uapi/linux/fsverity.h
> @@ -85,6 +85,7 @@ struct fsverity_formatted_digest {
>
> #define FS_VERITY_METADATA_TYPE_MERKLE_TREE 1
> #define FS_VERITY_METADATA_TYPE_DESCRIPTOR 2
> +#define FS_VERITY_METADATA_TYPE_SIGNATURE 3
>
> struct fsverity_read_metadata_arg {
> __u64 metadata_type;
> --
> 2.30.0
