1#define _GNU_SOURCE
 2#include <sched.h>
 3#include <unistd.h>
 4#include <stdio.h>
 5#include <stdlib.h>
 6#include <signal.h>
 7#include <errno.h>
 8#include <sys/types.h>
 9#include <sys/stat.h>
10#include <fcntl.h>
11#include <sys/ioctl.h>
12#include <sys/prctl.h>
13#include <sys/wait.h>
14
15#define pr_err(fmt, ...) \
16		({ \
17			fprintf(stderr, "%s:%d:" fmt ": %m\n", \
18				__func__, __LINE__, ##__VA_ARGS__); \
19			1; \
20		})
21
22#define NSIO	0xb7
23#define NS_GET_USERNS   _IO(NSIO, 0x1)
24#define NS_GET_PARENT   _IO(NSIO, 0x2)
25
26#define __stack_aligned__	__attribute__((aligned(16)))
27struct cr_clone_arg {
28	char stack[128] __stack_aligned__;
29	char stack_ptr[0];
30};
31
32static int child(void *args)
33{
34	prctl(PR_SET_PDEATHSIG, SIGKILL);
35	while (1)
36		sleep(1);
37	exit(0);
38}
39
40int main(int argc, char *argv[])
41{
42	char *ns_strs[] = {"pid", "user"};
43	char path[] = "/proc/0123456789/ns/pid";
44	struct cr_clone_arg ca;
45	struct stat st1, st2;
46	int ns, pns, i;
47	pid_t pid;
48
49	pid = clone(child, ca.stack_ptr, CLONE_NEWUSER | CLONE_NEWPID | SIGCHLD, NULL);
50	if (pid < 0)
51		return pr_err("clone");
52
53	for (i = 0; i < 2; i++) {
54		snprintf(path, sizeof(path), "/proc/%d/ns/%s", pid, ns_strs[i]);
55		ns = open(path, O_RDONLY);
56		if (ns < 0)
57			return pr_err("Unable to open %s", path);
58
59		pns = ioctl(ns, NS_GET_PARENT);
60		if (pns < 0)
61			return pr_err("Unable to get a parent pidns");
62
63		snprintf(path, sizeof(path), "/proc/self/ns/%s", ns_strs[i]);
64		if (stat(path, &st2))
65			return pr_err("Unable to stat %s", path);
66		if (fstat(pns, &st1))
67			return pr_err("Unable to stat the parent pidns");
68		if (st1.st_ino != st2.st_ino)
69			return pr_err("NS_GET_PARENT returned a wrong namespace");
70
71		if (ioctl(pns, NS_GET_PARENT) >= 0 || errno != EPERM)
72			return pr_err("Don't get EPERM");;
73	}
74
75	kill(pid, SIGKILL);
76	wait(NULL);
77	return 0;
78}