Pass along the child exit status

For some strange reason we cannot use WNOHANG in the options for
waitpid, otherwise it will always return 0.
This might be another kernel bug with seccomp we would have to
investigate, as this does not make any sense since the child has
obviously exited.

However, with this we finally imitate the exit code of the supervised
process.

Author: vimpostor

src/bin/seccomp/seccomp_exec.c

@@ -99,9 +99,17 @@ int seccomp_parent(struct seccomp_state *state) {
 		memset(req, 0, sizes.seccomp_notif);
 		if (ioctl(state->listener, SECCOMP_IOCTL_NOTIF_RECV, req)) {
 			if (errno == ENOENT) {
-				// when the child exits, SECCOMP_IOCTL_NOTIF_RECV will return with ENOENT,
-				// in which case we can also just quit the supervisor
-				exit_code = EXIT_SUCCESS;
+				// When the child exits, SECCOMP_IOCTL_NOTIF_RECV will return with ENOENT,
+				// in which case we can also just quit the supervisor.
+				// But first we have to retrieve the child's exit code
+				int wstatus;
+				pid_t wait = waitpid(state->task_pid, &wstatus, WUNTRACED | WCONTINUED);
+				if (wait != state->task_pid || !WIFEXITED(wstatus)) {
+					exit_code = EXIT_FAILURE;
+				} else {
+					// Pass over the same exit code
+					exit_code = WEXITSTATUS(wstatus);
+				}
 			} else {
 				perror("ioctl recv");
 			}