fs/ecryptfs/mmap.c

Source file repositories/reference/linux-study-clean/fs/ecryptfs/mmap.c

File Facts

System
Linux kernel
Corpus path
fs/ecryptfs/mmap.c
Extension
.c
Size
15574 bytes
Lines
535
Domain
Core OS
Bucket
VFS And Filesystem Core
Inferred role
Core OS: implementation source
Status
source implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

if (error) {
			ecryptfs_printk(KERN_WARNING,
				"Error encrypting folio (index [0x%.16lx])\n",
				folio->index);
			folio_clear_uptodate(folio);
			mapping_set_error(mapping, error);
		}
		folio_unlock(folio);
	}

	return error;
}

static void strip_xattr_flag(char *page_virt,
			     struct ecryptfs_crypt_stat *crypt_stat)
{
	if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
		size_t written;

		crypt_stat->flags &= ~ECRYPTFS_METADATA_IN_XATTR;
		ecryptfs_write_crypt_stat_flags(page_virt, crypt_stat,
						&written);
		crypt_stat->flags |= ECRYPTFS_METADATA_IN_XATTR;
	}
}

/*
 *   Header Extent:
 *     Octets 0-7:        Unencrypted file size (big-endian)
 *     Octets 8-15:       eCryptfs special marker
 *     Octets 16-19:      Flags
 *      Octet 16:         File format version number (between 0 and 255)
 *      Octets 17-18:     Reserved
 *      Octet 19:         Bit 1 (lsb): Reserved
 *                        Bit 2: Encrypted?
 *                        Bits 3-8: Reserved
 *     Octets 20-23:      Header extent size (big-endian)
 *     Octets 24-25:      Number of header extents at front of file
 *                        (big-endian)
 *     Octet  26:         Begin RFC 2440 authentication token packet set
 */

/**
 * ecryptfs_copy_up_encrypted_with_header
 * @folio: Sort of a ``virtual'' representation of the encrypted lower
 *        file. The actual lower file does not have the metadata in
 *        the header. This is locked.
 * @crypt_stat: The eCryptfs inode's cryptographic context
 *
 * The ``view'' is the version of the file that userspace winds up
 * seeing, with the header information inserted.
 */
static int
ecryptfs_copy_up_encrypted_with_header(struct folio *folio,
				       struct ecryptfs_crypt_stat *crypt_stat)
{
	loff_t extent_num_in_page = 0;
	loff_t num_extents_per_page = (PAGE_SIZE
				       / crypt_stat->extent_size);
	int rc = 0;

	while (extent_num_in_page < num_extents_per_page) {
		loff_t view_extent_num = ((loff_t)folio->index
					   * num_extents_per_page)
					  + extent_num_in_page;
		size_t num_header_extents_at_front =
			(crypt_stat->metadata_size / crypt_stat->extent_size);

		if (view_extent_num < num_header_extents_at_front) {
			/* This is a header extent */
			char *page_virt;

			page_virt = kmap_local_folio(folio, 0);
			memset(page_virt, 0, PAGE_SIZE);
			/* TODO: Support more than one header extent */
			if (view_extent_num == 0) {
				size_t written;

				rc = ecryptfs_read_xattr_region(
					page_virt, folio->mapping->host);
				strip_xattr_flag(page_virt + 16, crypt_stat);
				ecryptfs_write_header_metadata(page_virt + 20,
							       crypt_stat,
							       &written);
			}
			kunmap_local(page_virt);
			flush_dcache_folio(folio);
			if (rc) {
				printk(KERN_ERR "%s: Error reading xattr "
				       "region; rc = [%d]\n", __func__, rc);

Annotation

Implementation Notes