selftests: safesetid: Check the return value of setuid/setgid

Check the return value of setuid() and setgid().
This fixes the following warnings and improves test result.

safesetid-test.c: In function ‘main’:
safesetid-test.c:294:2: warning: ignoring return value of ‘setuid’, declared with attribute warn_unused_result [-Wunused-result]
  setuid(NO_POLICY_USER);
  ^~~~~~~~~~~~~~~~~~~~~~
safesetid-test.c:295:2: warning: ignoring return value of ‘setgid’, declared with attribute warn_unused_result [-Wunused-result]
  setgid(NO_POLICY_USER);
  ^~~~~~~~~~~~~~~~~~~~~~
safesetid-test.c:309:2: warning: ignoring return value of ‘setuid’, declared with attribute warn_unused_result [-Wunused-result]
  setuid(RESTRICTED_PARENT);
  ^~~~~~~~~~~~~~~~~~~~~~~~~
safesetid-test.c:310:2: warning: ignoring return value of ‘setgid’, declared with attribute warn_unused_result [-Wunused-result]
  setgid(RESTRICTED_PARENT);
  ^~~~~~~~~~~~~~~~~~~~~~~~~
safesetid-test.c: In function ‘test_setuid’:
safesetid-test.c:216:3: warning: ignoring return value of ‘setuid’, declared with attribute warn_unused_result [-Wunused-result]
   setuid(child_uid);
   ^~~~~~~~~~~~~~~~~

Fixes: c67e8ec0 ("LSM: SafeSetID: add selftest")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/safesetid/safesetid-test.c

@@ -213,7 +213,8 @@ static void test_setuid(uid_t child_uid, bool expect_success)
 	}
 
 	if (cpid == 0) {	    /* Code executed by child */
-		setuid(child_uid);
+		if (setuid(child_uid) < 0)
+			exit(EXIT_FAILURE);
 		if (getuid() == child_uid)
 			exit(EXIT_SUCCESS);
 		else
@@ -291,8 +292,10 @@ int main(int argc, char **argv)
 
 	// First test to make sure we can write userns mappings from a user
 	// that doesn't have any restrictions (as long as it has CAP_SETUID);
-	setuid(NO_POLICY_USER);
-	setgid(NO_POLICY_USER);
+	if (setuid(NO_POLICY_USER) < 0)
+		die("Error with set uid(%d)\n", NO_POLICY_USER);
+	if (setgid(NO_POLICY_USER) < 0)
+		die("Error with set gid(%d)\n", NO_POLICY_USER);
 
 	// Take away all but setid caps
 	drop_caps(true);
@@ -306,8 +309,10 @@ int main(int argc, char **argv)
 		die("test_userns failed when it should work\n");
 	}
 
-	setuid(RESTRICTED_PARENT);
-	setgid(RESTRICTED_PARENT);
+	if (setuid(RESTRICTED_PARENT) < 0)
+		die("Error with set uid(%d)\n", RESTRICTED_PARENT);
+	if (setgid(RESTRICTED_PARENT) < 0)
+		die("Error with set gid(%d)\n", RESTRICTED_PARENT);
 
 	test_setuid(ROOT_USER, false);
 	test_setuid(ALLOWED_CHILD1, true);