setns apparmor bug

README.md

Usage instructions:

make
sudo snap install snapd-hacker-toolbelt --devmode
sudo snapd-hacker-toolbelt.busybox sh
./oops

Makefile

.PHONY: all clean
CFLAGS += -Wall
all: oops
clean:
	rm -f oops

oops.c

#define _GNU_SOURCE

#include <fcntl.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

int main(void)
{
    int fd = open("/proc/1/ns/mnt", O_RDONLY | O_CLOEXEC | O_PATH);
    if (fd < 0) {
        perror("cannot open");
        return 1;
    }
    if (setns(fd, CLONE_NEWNS) < 0) {
        perror("cannot setns");
        return 1;
    };
    if (close(fd) < 0) {
        perror("cannot close");
        return 1;
    }
    return 0;
}