From: Eric Biggers <ebiggers@xxxxxxxxxx>
Add support for FS_VERITY_METADATA_TYPE_MERKLE_TREE to
FS_IOC_READ_VERITY_METADATA. This allows a userspace server program to
retrieve the Merkle tree 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.
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 | 10 +++-
fs/verity/read_metadata.c | 70 ++++++++++++++++++++++++++
include/uapi/linux/fsverity.h | 2 +
3 files changed, 81 insertions(+), 1 deletion(-)
diff --git a/Documentation/filesystems/fsverity.rst b/Documentation/filesystems/fsverity.rst
index 9ef7a7de60085..50b47a6d9ea11 100644
--- a/Documentation/filesystems/fsverity.rst
+++ b/Documentation/filesystems/fsverity.rst
@@ -234,6 +234,8 @@ need this ioctl.
This ioctl takes in a pointer to the following structure::
+ #define FS_VERITY_METADATA_TYPE_MERKLE_TREE 1
+
struct fsverity_read_metadata_arg {
__u64 metadata_type;
__u64 offset;
@@ -242,7 +244,13 @@ This ioctl takes in a pointer to the following structure::
__u64 __reserved;
};
-``metadata_type`` specifies the type of metadata to read.
+``metadata_type`` specifies the type of metadata to read:
+
+- ``FS_VERITY_METADATA_TYPE_MERKLE_TREE`` reads the blocks of the
+ Merkle tree. The blocks are returned in order from the root level
+ to the leaf level. Within each level, the blocks are returned in
+ the same order that their hashes are themselves hashed.
+ See `Merkle tree`_ for more information.
The semantics are similar to those of ``pread()``. ``offset``
specifies the offset in bytes into the metadata item to read from, and
diff --git a/fs/verity/read_metadata.c b/fs/verity/read_metadata.c
index 43be990fd53e4..0f8ad2991cf90 100644
--- a/fs/verity/read_metadata.c
+++ b/fs/verity/read_metadata.c
@@ -7,8 +7,75 @@
#include "fsverity_private.h"
+#include <linux/backing-dev.h>
+#include <linux/highmem.h>
+#include <linux/sched/signal.h>
#include <linux/uaccess.h>
+static int fsverity_read_merkle_tree(struct inode *inode,
+ const struct fsverity_info *vi,
+ void __user *buf, u64 offset, int length)
+{
+ const struct fsverity_operations *vops = inode->i_sb->s_vop;
+ u64 end_offset;
+ unsigned int offs_in_page;
+ pgoff_t index, last_index;
+ int retval = 0;
+ int err = 0;
+
+ end_offset = min(offset + length, vi->tree_params.tree_size);
+ if (offset >= end_offset)
+ return 0;
+ offs_in_page = offset_in_page(offset);
+ last_index = (end_offset - 1) >> PAGE_SHIFT;
+
+ /*
+ * Iterate through each Merkle tree page in the requested range and copy
+ * the requested portion to userspace. Note that the Merkle tree block
+ * size isn't important here, as we are returning a byte stream; i.e.,
+ * we can just work with pages even if the tree block size != PAGE_SIZE.
+ */
+ for (index = offset >> PAGE_SHIFT; index <= last_index; index++) {
+ unsigned long num_ra_pages =
+ min_t(unsigned long, last_index - index + 1,
+ inode->i_sb->s_bdi->io_pages);
+ unsigned int bytes_to_copy = min_t(u64, end_offset - offset,
+ PAGE_SIZE - offs_in_page);
+ struct page *page;
+ const void *virt;
+
+ page = vops->read_merkle_tree_page(inode, index, num_ra_pages);
+ if (IS_ERR(page)) {
+ err = PTR_ERR(page);
+ fsverity_err(inode,
+ "Error %d reading Merkle tree page %lu",
+ err, index);
+ break;
+ }
+
+ virt = kmap(page);
+ if (copy_to_user(buf, virt + offs_in_page, bytes_to_copy)) {
+ kunmap(page);
+ put_page(page);
+ err = -EFAULT;
+ break;
+ }
+ kunmap(page);
+ put_page(page);
+
+ retval += bytes_to_copy;
+ buf += bytes_to_copy;
+ offset += bytes_to_copy;
+
+ if (fatal_signal_pending(current)) {
+ err = -EINTR;
+ break;
+ }
+ cond_resched();
+ offs_in_page = 0;
+ }
+ return retval ? retval : err;
+}
/**
* fsverity_ioctl_read_metadata() - read verity metadata from a file
* @filp: file to read the metadata from
@@ -48,6 +115,9 @@ int fsverity_ioctl_read_metadata(struct file *filp, const void __user *uarg)
buf = u64_to_user_ptr(arg.buf_ptr);
switch (arg.metadata_type) {
+ case FS_VERITY_METADATA_TYPE_MERKLE_TREE:
+ return fsverity_read_merkle_tree(inode, vi, buf, arg.offset,
+ length);
default:
return -EINVAL;
}
diff --git a/include/uapi/linux/fsverity.h b/include/uapi/linux/fsverity.h
index e062751294d01..94003b153cb3d 100644
--- a/include/uapi/linux/fsverity.h
+++ b/include/uapi/linux/fsverity.h
@@ -83,6 +83,8 @@ struct fsverity_formatted_digest {
__u8 digest[];
};
+#define FS_VERITY_METADATA_TYPE_MERKLE_TREE 1
+
struct fsverity_read_metadata_arg {
__u64 metadata_type;
__u64 offset;
--
2.30.0
