efi_loader: correct find simple file system protocol

In contrast to the description the code did not split the device
path into device part and file part.

The code should use the installed protocol and not refer to the
internal structure of the the disk object.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>

lib/efi_loader/efi_disk.c

@@ -175,25 +175,44 @@ static const struct efi_block_io block_io_disk_template = {
 };
 
 /*
- * Find filesystem from a device-path.  The passed in path 'p' probably
- * contains one or more /File(name) nodes, so the comparison stops at
- * the first /File() node, and returns the pointer to that via 'rp'.
- * This is mostly intended to be a helper to map a device-path to an
- * efi_file_handle object.
+ * Get the simple file system protocol for a file device path.
+ *
+ * The full path provided is split into device part and into a file
+ * part. The device part is used to find the handle on which the
+ * simple file system protocol is installed.
+ *
+ * @full_path	device path including device and file
+ * @return	simple file system protocol
  */
 struct efi_simple_file_system_protocol *
-efi_fs_from_path(struct efi_device_path *fp)
+efi_fs_from_path(struct efi_device_path *full_path)
 {
 	struct efi_object *efiobj;
-	struct efi_disk_obj *diskobj;
+	struct efi_handler *handler;
+	struct efi_device_path *device_path;
+	struct efi_device_path *file_path;
+	efi_status_t ret;
 
-	efiobj = efi_dp_find_obj(fp, NULL);
+	/* Split the path into a device part and a file part */
+	ret = efi_dp_split_file_path(full_path, &device_path, &file_path);
+	if (ret != EFI_SUCCESS)
+		return NULL;
+	efi_free_pool(file_path);
+
+	/* Get the EFI object for the partition */
+	efiobj = efi_dp_find_obj(device_path, NULL);
+	efi_free_pool(device_path);
 	if (!efiobj)
 		return NULL;
 
-	diskobj = container_of(efiobj, struct efi_disk_obj, parent);
+	/* Find the simple file system protocol */
+	ret = efi_search_protocol(efiobj, &efi_simple_file_system_protocol_guid,
+				  &handler);
+	if (ret != EFI_SUCCESS)
+		return NULL;
 
-	return diskobj->volume;
+	/* Return the simple file system protocol for the partition */
+	return handler->protocol_interface;
 }
 
 /*