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/* Copyright (c) 2016 Sargun Dhillon <sargun@sargun.me>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of version 2 of the GNU General Public
* License as published by the Free Software Foundation.
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <linux/bpf.h>
#include <unistd.h>
#include "libbpf.h"
#include "bpf_load.h"
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <linux/bpf.h>
#include <sched.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <linux/limits.h>
#define CGROUP_MOUNT_PATH "/mnt"
#define CGROUP_PATH "/mnt/my-cgroup"
#define clean_errno() (errno == 0 ? "None" : strerror(errno))
#define log_err(MSG, ...) fprintf(stderr, "(%s:%d: errno: %s) " MSG "\n", \
__FILE__, __LINE__, clean_errno(), ##__VA_ARGS__)
static int join_cgroup(char *path)
{
int fd, rc = 0;
pid_t pid = getpid();
char cgroup_path[PATH_MAX + 1];
snprintf(cgroup_path, sizeof(cgroup_path), "%s/cgroup.procs", path);
fd = open(cgroup_path, O_WRONLY);
if (fd < 0) {
log_err("Opening Cgroup");
return 1;
}
if (dprintf(fd, "%d\n", pid) < 0) {
log_err("Joining Cgroup");
rc = 1;
}
close(fd);
return rc;
}
int main(int argc, char **argv)
{
char filename[256];
int cg2, idx = 0;
pid_t remote_pid, local_pid = getpid();
snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
if (load_bpf_file(filename)) {
printf("%s", bpf_log_buf);
return 1;
}
/*
* This is to avoid interfering with existing cgroups. Unfortunately,
* most people don't have cgroupv2 enabled at this point in time.
* It's easier to create our own mount namespace and manage it
* ourselves.
*/
if (unshare(CLONE_NEWNS)) {
log_err("unshare");
return 1;
}
if (mount("none", "/", NULL, MS_REC | MS_PRIVATE, NULL)) {
log_err("mount fakeroot");
return 1;
}
if (mount("none", CGROUP_MOUNT_PATH, "cgroup2", 0, NULL)) {
log_err("mount cgroup2");
return 1;
}
if (mkdir(CGROUP_PATH, 0777) && errno != EEXIST) {
log_err("mkdir cgroup");
return 1;
}
cg2 = open(CGROUP_PATH, O_RDONLY);
if (cg2 < 0) {
log_err("opening target cgroup");
goto cleanup_cgroup_err;
}
if (bpf_update_elem(map_fd[0], &idx, &cg2, BPF_ANY)) {
log_err("Adding target cgroup to map");
goto cleanup_cgroup_err;
}
if (join_cgroup("/mnt/my-cgroup")) {
log_err("Leaving target cgroup");
goto cleanup_cgroup_err;
}
/*
* The installed helper program catched the sync call, and should
* write it to the map.
*/
sync();
bpf_lookup_elem(map_fd[1], &idx, &remote_pid);
if (local_pid != remote_pid) {
fprintf(stderr,
"BPF Helper didn't write correct PID to map, but: %d\n",
remote_pid);
goto leave_cgroup_err;
}
/* Verify the negative scenario; leave the cgroup */
if (join_cgroup(CGROUP_MOUNT_PATH))
goto leave_cgroup_err;
remote_pid = 0;
bpf_update_elem(map_fd[1], &idx, &remote_pid, BPF_ANY);
sync();
bpf_lookup_elem(map_fd[1], &idx, &remote_pid);
if (local_pid == remote_pid) {
fprintf(stderr, "BPF cgroup negative test did not work\n");
goto cleanup_cgroup_err;
}
rmdir(CGROUP_PATH);
return 0;
/* Error condition, cleanup */
leave_cgroup_err:
join_cgroup(CGROUP_MOUNT_PATH);
cleanup_cgroup_err:
rmdir(CGROUP_PATH);
return 1;
}
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