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fs-verity: support reading signature with ioctl

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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.

Link: https://lore.kernel.org/r/20210115181819.34732-7-ebiggers@kernel.org
Reviewed-by: Victor Hsieh <victorhsieh@google.com>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
This commit is contained in:
Eric Biggers
2021-01-15 10:18:19 -08:00
committed by Jaegeuk Kim
parent 99e8c45190
commit 4336e78b27
3 changed files with 39 additions and 1 deletions
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9
Documentation/filesystems/fsverity.rst
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@@ -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