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-rw-r--r--fs/verity/read_metadata.c194
1 files changed, 194 insertions, 0 deletions
diff --git a/fs/verity/read_metadata.c b/fs/verity/read_metadata.c
new file mode 100644
index 000000000..2aefc5565
--- /dev/null
+++ b/fs/verity/read_metadata.c
@@ -0,0 +1,194 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Ioctl to read verity metadata
+ *
+ * Copyright 2021 Google LLC
+ */
+
+#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_local_page(page);
+ if (copy_to_user(buf, virt + offs_in_page, bytes_to_copy)) {
+ kunmap_local(virt);
+ put_page(page);
+ err = -EFAULT;
+ break;
+ }
+ kunmap_local(virt);
+ 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;
+}
+
+/* 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);
+ 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;
+}
+
+static int fsverity_read_signature(struct inode *inode,
+ void __user *buf, u64 offset, int length)
+{
+ struct fsverity_descriptor *desc;
+ int res;
+
+ res = fsverity_get_descriptor(inode, &desc);
+ 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
+ * @uarg: user pointer to fsverity_read_metadata_arg
+ *
+ * Return: length read on success, 0 on EOF, -errno on failure
+ */
+int fsverity_ioctl_read_metadata(struct file *filp, const void __user *uarg)
+{
+ struct inode *inode = file_inode(filp);
+ const struct fsverity_info *vi;
+ struct fsverity_read_metadata_arg arg;
+ int length;
+ void __user *buf;
+
+ vi = fsverity_get_info(inode);
+ if (!vi)
+ return -ENODATA; /* not a verity file */
+ /*
+ * Note that we don't have to explicitly check that the file is open for
+ * reading, since verity files can only be opened for reading.
+ */
+
+ if (copy_from_user(&arg, uarg, sizeof(arg)))
+ return -EFAULT;
+
+ if (arg.__reserved)
+ return -EINVAL;
+
+ /* offset + length must not overflow. */
+ if (arg.offset + arg.length < arg.offset)
+ return -EINVAL;
+
+ /* Ensure that the return value will fit in INT_MAX. */
+ length = min_t(u64, arg.length, INT_MAX);
+
+ 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);
+ 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;
+ }
+}
+EXPORT_SYMBOL_GPL(fsverity_ioctl_read_metadata);