Why QDir::exists() do not work in docker container?

Question

The following program executed in my host KDE Neon machine (up to date upgraded to 18.04) outputs Hello World! 1 as expected while it outputs Hello World! 0 when executed from a Docker container built using the Dockerfile below and running with sudo docker run -it qdir.

Does QDir need dbus or another service running ?

C++ program:

#include <QDir>
#include <iostream>


int main(int argc [[maybe_unused]], char** argv [[maybe_unused]])
{
    QDir d("/");
    std::cout << "Hello World! " << d.exists() << std::endl;
    return 0;
}

Dockerfile:

FROM kdeneon/plasma:user-lts

USER root

RUN apt-get install -y qt5-default

WORKDIR /
COPY qdir /
CMD /bin/bash

Edit, CMakeLists.txt to build the program:

project(qdir)

cmake_minimum_required(VERSION 2.8.12 FATAL_ERROR)
set(QT_MIN_VERSION "5.3.0")

find_package(Qt5 ${QT_MIN_VERSION} CONFIG REQUIRED COMPONENTS Core)

include_directories(${Qt5Core_INCLUDE_DIRS} ${CMAKE_CURRENT_BINARY_DIR})

set(qdir_SRCS main.cpp)

add_executable(qdir ${qdir_SRCS})
target_link_libraries(qdir ${Qt5Core_LIBRARIES})

install(TARGETS qdir RUNTIME DESTINATION bin)

Edit2: I created a github project regrouping all of the above. To reproduce the problem, if you have the Qt SDK, cmake, ninja and docker, just do:

git clone https://github.com/kleag/qdirtest
cd qdirtest
./test.sh

This is the output I get:

$ ./test.sh
[…]
Successfully built f710cbb7a3c9
Successfully tagged qdir:latest
Hello World! 1
Hello World! 0

Answer 1

I got the answer from apachelogger on KDE forums:

Since 5.10 Qt is using somewhat new syscalls. One of them is statx and last I checked the syscall was not whitelisted in docker, nor was it whitelistable because the libseccomp used for the upstream docker build was too old and didn't know what statx is. Chances are the problem you see is that. If so, seccomp=unconfined would make it work.