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