[PATCH v2 08/10] landlock: Change landlock_add_rule(2) argument check ordering

["Mickaël Salaün" <mic@digikod.net>]

This makes more sense to first check the ruleset FD and then the rule
attribute.  It will be useful to factor out code for other rule types.

Add inval_add_rule_arguments tests, extension of empty_path_beneath_attr
tests, to also check error ordering for landlock_add_rule(2).

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20220506160820.524344-9-mic@digikod.net
---

Changes since v1:
* New patch.
---
 security/landlock/syscalls.c                 | 22 +++++++------
 tools/testing/selftests/landlock/base_test.c | 34 ++++++++++++++++++--
 2 files changed, 45 insertions(+), 11 deletions(-)

diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
index 7edc1d50e2bf..a7396220c9d4 100644
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -318,20 +318,24 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
 	if (flags)
 		return -EINVAL;
 
-	if (rule_type != LANDLOCK_RULE_PATH_BENEATH)
-		return -EINVAL;
-
-	/* 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;
-
 	/* Gets and checks the ruleset. */
 	ruleset = get_ruleset_from_fd(ruleset_fd, FMODE_CAN_WRITE);
 	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.
diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c
index be9b937256ac..18b779471dcb 100644
--- a/tools/testing/selftests/landlock/base_test.c
+++ b/tools/testing/selftests/landlock/base_test.c
@@ -121,20 +121,50 @@ TEST(inval_create_ruleset_flags)
 	ASSERT_EQ(EINVAL, errno);
 }
 
-TEST(empty_path_beneath_attr)
+/* Tests ordering of syscall argument checks. */
+TEST(add_rule_checks_ordering)
 {
 	const struct landlock_ruleset_attr ruleset_attr = {
 		.handled_access_fs = LANDLOCK_ACCESS_FS_EXECUTE,
 	};
+	struct landlock_path_beneath_attr path_beneath_attr = {
+		.allowed_access = LANDLOCK_ACCESS_FS_EXECUTE,
+		.parent_fd = -1,
+	};
 	const int ruleset_fd =
 		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
 
 	ASSERT_LE(0, ruleset_fd);
 
-	/* Similar to struct landlock_path_beneath_attr.parent_fd = 0 */
+	/* Checks invalid flags. */
+	ASSERT_EQ(-1, landlock_add_rule(-1, 0, NULL, 1));
+	ASSERT_EQ(EINVAL, errno);
+
+	/* Checks invalid ruleset FD. */
+	ASSERT_EQ(-1, landlock_add_rule(-1, 0, NULL, 0));
+	ASSERT_EQ(EBADF, errno);
+
+	/* Checks invalid rule type. */
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, 0, NULL, 0));
+	ASSERT_EQ(EINVAL, errno);
+
+	/* Checks invalid rule attr. */
 	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
 					NULL, 0));
 	ASSERT_EQ(EFAULT, errno);
+
+	/* Checks invalid path_beneath.parent_fd. */
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+					&path_beneath_attr, 0));
+	ASSERT_EQ(EBADF, errno);
+
+	/* Checks valid call. */
+	path_beneath_attr.parent_fd =
+		open("/tmp", O_PATH | O_NOFOLLOW | O_DIRECTORY | O_CLOEXEC);
+	ASSERT_LE(0, path_beneath_attr.parent_fd);
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				       &path_beneath_attr, 0));
+	ASSERT_EQ(0, close(path_beneath_attr.parent_fd));
 	ASSERT_EQ(0, close(ruleset_fd));
 }
 
-- 
2.35.1