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// SPDX-License-Identifier: GPL-2.0
#define _GNU_SOURCE
#include <sched.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/prctl.h>
#include <sys/wait.h>
#define NSIO 0xb7
#define NS_GET_USERNS _IO(NSIO, 0x1)
#define pr_err(fmt, ...) \
({ \
fprintf(stderr, "%s:%d:" fmt ": %m\n", \
__func__, __LINE__, ##__VA_ARGS__); \
1; \
})
int main(int argc, char *argvp[])
{
int pfd[2], ns, uns, init_uns;
struct stat st1, st2;
char path[128];
pid_t pid;
char c;
if (pipe(pfd))
return 1;
pid = fork();
if (pid < 0)
return pr_err("fork");
if (pid == 0) {
prctl(PR_SET_PDEATHSIG, SIGKILL);
if (unshare(CLONE_NEWUTS | CLONE_NEWUSER))
return pr_err("unshare");
close(pfd[0]);
close(pfd[1]);
while (1)
sleep(1);
return 0;
}
close(pfd[1]);
if (read(pfd[0], &c, 1) != 0)
return pr_err("Unable to read from pipe");
close(pfd[0]);
snprintf(path, sizeof(path), "/proc/%d/ns/uts", pid);
ns = open(path, O_RDONLY);
if (ns < 0)
return pr_err("Unable to open %s", path);
uns = ioctl(ns, NS_GET_USERNS);
if (uns < 0)
return pr_err("Unable to get an owning user namespace");
if (fstat(uns, &st1))
return pr_err("fstat");
snprintf(path, sizeof(path), "/proc/%d/ns/user", pid);
if (stat(path, &st2))
return pr_err("stat");
if (st1.st_ino != st2.st_ino)
return pr_err("NS_GET_USERNS returned a wrong namespace");
init_uns = ioctl(uns, NS_GET_USERNS);
if (uns < 0)
return pr_err("Unable to get an owning user namespace");
if (ioctl(init_uns, NS_GET_USERNS) >= 0 || errno != EPERM)
return pr_err("Don't get EPERM");
if (unshare(CLONE_NEWUSER))
return pr_err("unshare");
if (ioctl(ns, NS_GET_USERNS) >= 0 || errno != EPERM)
return pr_err("Don't get EPERM");
if (ioctl(init_uns, NS_GET_USERNS) >= 0 || errno != EPERM)
return pr_err("Don't get EPERM");
kill(pid, SIGKILL);
wait(NULL);
return 0;
}
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