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