eCryptfs: Strip metadata in xattr flag in encrypted view

The ecryptfs_encrypted_view mount option provides a unified way of
viewing encrypted eCryptfs files. If the metadata is stored in a xattr,
the metadata is moved to the file header when the file is read inside
the eCryptfs mount. Because of this, we should strip the
ECRYPTFS_METADATA_IN_XATTR flag from the header's flag section. This
allows eCryptfs to treat the file as an eCryptfs file with a header
at the front.

Reviewed-by: Eric Sandeen <[e-mail]>
Signed-off-by: Tyler Hicks <[e-mail]>

fs/ecryptfs/crypto.c

···
 	(*written) = MAGIC_ECRYPTFS_MARKER_SIZE_BYTES;
 }
 
-static void
-write_ecryptfs_flags(char *page_virt, struct ecryptfs_crypt_stat *crypt_stat,
-		     size_t *written)
+void ecryptfs_write_crypt_stat_flags(char *page_virt,
+				     struct ecryptfs_crypt_stat *crypt_stat,
+				     size_t *written)
 {
 	u32 flags = 0;
 	int i;
···
 	offset = ECRYPTFS_FILE_SIZE_BYTES;
 	write_ecryptfs_marker((page_virt + offset), &written);
 	offset += written;
-	write_ecryptfs_flags((page_virt + offset), crypt_stat, &written);
+	ecryptfs_write_crypt_stat_flags((page_virt + offset), crypt_stat,
+					&written);
 	offset += written;
 	ecryptfs_write_header_metadata((page_virt + offset), crypt_stat,
 				       &written);

fs/ecryptfs/ecryptfs_kernel.h

···
 int ecryptfs_write_metadata(struct dentry *ecryptfs_dentry);
 int ecryptfs_read_metadata(struct dentry *ecryptfs_dentry);
 int ecryptfs_new_file_context(struct dentry *ecryptfs_dentry);
+void ecryptfs_write_crypt_stat_flags(char *page_virt,
+				     struct ecryptfs_crypt_stat *crypt_stat,
+				     size_t *written);
 int ecryptfs_read_and_validate_header_region(char *data,
 					     struct inode *ecryptfs_inode);
 int ecryptfs_read_and_validate_xattr_region(char *page_virt,

fs/ecryptfs/mmap.c

···
 	return rc;
 }
 
+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)
···
 
 				rc = ecryptfs_read_xattr_region(
 					page_virt, page->mapping->host);
+				strip_xattr_flag(page_virt + 16, crypt_stat);
 				ecryptfs_write_header_metadata(page_virt + 20,
 							       crypt_stat,
 							       &written);