landlock: Refactor landlock_add_rule() syscall

Change the landlock_add_rule() syscall to support new rule types with
next commits. Add the add_rule_path_beneath() helper to support current
filesystem rules.
Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
Link: https://lore.kernel.org/r/20231026014751.414649-8-konstantin.meskhidze@huawei.comSigned-off-by: Mickaël Salaün <mic@digikod.net>

security/landlock/syscalls.c

@@ -274,6 +274,44 @@ static int get_path_from_fd(const s32 fd, struct path *const path)
 	return err;
 }
 
+static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
+				 const void __user *const rule_attr)
+{
+	struct landlock_path_beneath_attr path_beneath_attr;
+	struct path path;
+	int res, err;
+	access_mask_t mask;
+
+	/* Copies raw user space buffer, only one type for now. */
+	res = copy_from_user(&path_beneath_attr, rule_attr,
+			     sizeof(path_beneath_attr));
+	if (res)
+		return -EFAULT;
+
+	/*
+	 * Informs about useless rule: empty allowed_access (i.e. deny rules)
+	 * are ignored in path walks.
+	 */
+	if (!path_beneath_attr.allowed_access)
+		return -ENOMSG;
+
+	/* Checks that allowed_access matches the @ruleset constraints. */
+	mask = landlock_get_raw_fs_access_mask(ruleset, 0);
+	if ((path_beneath_attr.allowed_access | mask) != mask)
+		return -EINVAL;
+
+	/* Gets and checks the new rule. */
+	err = get_path_from_fd(path_beneath_attr.parent_fd, &path);
+	if (err)
+		return err;
+
+	/* Imports the new rule. */
+	err = landlock_append_fs_rule(ruleset, &path,
+				      path_beneath_attr.allowed_access);
+	path_put(&path);
+	return err;
+}
+
 /**
  * sys_landlock_add_rule - Add a new rule to a ruleset
  *
@@ -306,11 +344,8 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
 		const enum landlock_rule_type, rule_type,
 		const void __user *const, rule_attr, const __u32, flags)
 {
-	struct landlock_path_beneath_attr path_beneath_attr;
-	struct path path;
 	struct landlock_ruleset *ruleset;
-	int res, err;
-	access_mask_t mask;
+	int err;
 
 	if (!landlock_initialized)
 		return -EOPNOTSUPP;
@@ -324,48 +359,14 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
 	if (IS_ERR(ruleset))
 		return PTR_ERR(ruleset);
 
-	if (rule_type != LANDLOCK_RULE_PATH_BENEATH) {
-		err = -EINVAL;
-		goto out_put_ruleset;
-	}
-
-	/* Copies raw user space buffer, only one type for now. */
-	res = copy_from_user(&path_beneath_attr, rule_attr,
-			     sizeof(path_beneath_attr));
-	if (res) {
-		err = -EFAULT;
-		goto out_put_ruleset;
-	}
-
-	/*
-	 * Informs about useless rule: empty allowed_access (i.e. deny rules)
-	 * are ignored in path walks.
-	 */
-	if (!path_beneath_attr.allowed_access) {
-		err = -ENOMSG;
-		goto out_put_ruleset;
-	}
-	/*
-	 * Checks that allowed_access matches the @ruleset constraints
-	 * (ruleset->access_masks[0] is automatically upgraded to 64-bits).
-	 */
-	mask = landlock_get_raw_fs_access_mask(ruleset, 0);
-	if ((path_beneath_attr.allowed_access | mask) != mask) {
+	switch (rule_type) {
+	case LANDLOCK_RULE_PATH_BENEATH:
+		err = add_rule_path_beneath(ruleset, rule_attr);
+		break;
+	default:
 		err = -EINVAL;
-		goto out_put_ruleset;
+		break;
 	}
-
-	/* Gets and checks the new rule. */
-	err = get_path_from_fd(path_beneath_attr.parent_fd, &path);
-	if (err)
-		goto out_put_ruleset;
-
-	/* Imports the new rule. */
-	err = landlock_append_fs_rule(ruleset, &path,
-				      path_beneath_attr.allowed_access);
-	path_put(&path);
-
-out_put_ruleset:
 	landlock_put_ruleset(ruleset);
 	return err;
 }