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>
---
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
