93 lines · c
1// SPDX-License-Identifier: GPL-2.02#define _GNU_SOURCE3#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 NSIO 0xb717#define NS_GET_USERNS _IO(NSIO, 0x1)18 19#define pr_err(fmt, ...) \20 ({ \21 fprintf(stderr, "%s:%d:" fmt ": %m\n", \22 __func__, __LINE__, ##__VA_ARGS__); \23 1; \24 })25 26int main(int argc, char *argvp[])27{28 int pfd[2], ns, uns, init_uns;29 struct stat st1, st2;30 char path[128];31 pid_t pid;32 char c;33 34 if (pipe(pfd))35 return 1;36 37 pid = fork();38 if (pid < 0)39 return pr_err("fork");40 if (pid == 0) {41 prctl(PR_SET_PDEATHSIG, SIGKILL);42 if (unshare(CLONE_NEWUTS | CLONE_NEWUSER))43 return pr_err("unshare");44 close(pfd[0]);45 close(pfd[1]);46 while (1)47 sleep(1);48 return 0;49 }50 close(pfd[1]);51 if (read(pfd[0], &c, 1) != 0)52 return pr_err("Unable to read from pipe");53 close(pfd[0]);54 55 snprintf(path, sizeof(path), "/proc/%d/ns/uts", pid);56 ns = open(path, O_RDONLY);57 if (ns < 0)58 return pr_err("Unable to open %s", path);59 60 uns = ioctl(ns, NS_GET_USERNS);61 if (uns < 0)62 return pr_err("Unable to get an owning user namespace");63 64 if (fstat(uns, &st1))65 return pr_err("fstat");66 67 snprintf(path, sizeof(path), "/proc/%d/ns/user", pid);68 if (stat(path, &st2))69 return pr_err("stat");70 71 if (st1.st_ino != st2.st_ino)72 return pr_err("NS_GET_USERNS returned a wrong namespace");73 74 init_uns = ioctl(uns, NS_GET_USERNS);75 if (uns < 0)76 return pr_err("Unable to get an owning user namespace");77 78 if (ioctl(init_uns, NS_GET_USERNS) >= 0 || errno != EPERM)79 return pr_err("Don't get EPERM");80 81 if (unshare(CLONE_NEWUSER))82 return pr_err("unshare");83 84 if (ioctl(ns, NS_GET_USERNS) >= 0 || errno != EPERM)85 return pr_err("Don't get EPERM");86 if (ioctl(init_uns, NS_GET_USERNS) >= 0 || errno != EPERM)87 return pr_err("Don't get EPERM");88 89 kill(pid, SIGKILL);90 wait(NULL);91 return 0;92}93