1 // SPDX-License-Identifier: GPL-2.0
2 #define _GNU_SOURCE
3 #include <sched.h>
4 #include <unistd.h>
5 #include <stdio.h>
6 #include <stdlib.h>
7 #include <signal.h>
8 #include <errno.h>
9 #include <sys/types.h>
10 #include <sys/stat.h>
11 #include <fcntl.h>
12 #include <sys/ioctl.h>
13 #include <sys/prctl.h>
14 #include <sys/wait.h>
15 
16 #define pr_err(fmt, ...) \
17 		({ \
18 			fprintf(stderr, "%s:%d:" fmt ": %m\n", \
19 				__func__, __LINE__, ##__VA_ARGS__); \
20 			1; \
21 		})
22 
23 #define NSIO	0xb7
24 #define NS_GET_USERNS   _IO(NSIO, 0x1)
25 #define NS_GET_PARENT   _IO(NSIO, 0x2)
26 
27 #define __stack_aligned__	__attribute__((aligned(16)))
28 struct cr_clone_arg {
29 	char stack[128] __stack_aligned__;
30 	char stack_ptr[0];
31 };
32 
33 static int child(void *args)
34 {
35 	prctl(PR_SET_PDEATHSIG, SIGKILL);
36 	while (1)
37 		sleep(1);
38 	exit(0);
39 }
40 
41 int main(int argc, char *argv[])
42 {
43 	char *ns_strs[] = {"pid", "user"};
44 	char path[] = "/proc/0123456789/ns/pid";
45 	struct cr_clone_arg ca;
46 	struct stat st1, st2;
47 	int ns, pns, i;
48 	pid_t pid;
49 
50 	pid = clone(child, ca.stack_ptr, CLONE_NEWUSER | CLONE_NEWPID | SIGCHLD, NULL);
51 	if (pid < 0)
52 		return pr_err("clone");
53 
54 	for (i = 0; i < 2; i++) {
55 		snprintf(path, sizeof(path), "/proc/%d/ns/%s", pid, ns_strs[i]);
56 		ns = open(path, O_RDONLY);
57 		if (ns < 0)
58 			return pr_err("Unable to open %s", path);
59 
60 		pns = ioctl(ns, NS_GET_PARENT);
61 		if (pns < 0)
62 			return pr_err("Unable to get a parent pidns");
63 
64 		snprintf(path, sizeof(path), "/proc/self/ns/%s", ns_strs[i]);
65 		if (stat(path, &st2))
66 			return pr_err("Unable to stat %s", path);
67 		if (fstat(pns, &st1))
68 			return pr_err("Unable to stat the parent pidns");
69 		if (st1.st_ino != st2.st_ino)
70 			return pr_err("NS_GET_PARENT returned a wrong namespace");
71 
72 		if (ioctl(pns, NS_GET_PARENT) >= 0 || errno != EPERM)
73 			return pr_err("Don't get EPERM");
74 	}
75 
76 	kill(pid, SIGKILL);
77 	wait(NULL);
78 	return 0;
79 }
80