samples/bpf/test_current_task_under_cgroup_user.c

   1 /* Copyright (c) 2016 Sargun Dhillon <sargun@sargun.me>
   2  *
   3  * This program is free software; you can redistribute it and/or
   4  * modify it under the terms of version 2 of the GNU General Public
   5  * License as published by the Free Software Foundation.
   6  */
   7
   8 #define _GNU_SOURCE
   9 #include <stdio.h>
  10 #include <linux/bpf.h>
  11 #include <unistd.h>
  12 #include "libbpf.h"
  13 #include "bpf_load.h"
  14 #include <string.h>
  15 #include <fcntl.h>
  16 #include <errno.h>
  17 #include <linux/bpf.h>
  18 #include <sched.h>
  19 #include <sys/mount.h>
  20 #include <sys/stat.h>
  21 #include <sys/types.h>
  22 #include <linux/limits.h>
  23
  24 #define CGROUP_MOUNT_PATH       "/mnt"
  25 #define CGROUP_PATH             "/mnt/my-cgroup"
  26
  27 #define clean_errno() (errno == 0 ? "None" : strerror(errno))
  28 #define log_err(MSG, ...) fprintf(stderr, "(%s:%d: errno: %s) " MSG "\n", \
  29         __FILE__, __LINE__, clean_errno(), ##__VA_ARGS__)
  30
  31 static int join_cgroup(char *path)
  32 {
  33         int fd, rc = 0;
  34         pid_t pid = getpid();
  35         char cgroup_path[PATH_MAX + 1];
  36
  37         snprintf(cgroup_path, sizeof(cgroup_path), "%s/cgroup.procs", path);
  38
  39         fd = open(cgroup_path, O_WRONLY);
  40         if (fd < 0) {
  41                 log_err("Opening Cgroup");
  42                 return 1;
  43         }
  44
  45         if (dprintf(fd, "%d\n", pid) < 0) {
  46                 log_err("Joining Cgroup");
  47                 rc = 1;
  48         }
  49         close(fd);
  50         return rc;
  51 }
  52
  53 int main(int argc, char **argv)
  54 {
  55         char filename[256];
  56         int cg2, idx = 0;
  57         pid_t remote_pid, local_pid = getpid();
  58
  59         snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
  60         if (load_bpf_file(filename)) {
  61                 printf("%s", bpf_log_buf);
  62                 return 1;
  63         }
  64
  65         /*
  66          * This is to avoid interfering with existing cgroups. Unfortunately,
  67          * most people don't have cgroupv2 enabled at this point in time.
  68          * It's easier to create our own mount namespace and manage it
  69          * ourselves.
  70          */
  71         if (unshare(CLONE_NEWNS)) {
  72                 log_err("unshare");
  73                 return 1;
  74         }
  75
  76         if (mount("none", "/", NULL, MS_REC | MS_PRIVATE, NULL)) {
  77                 log_err("mount fakeroot");
  78                 return 1;
  79         }
  80
  81         if (mount("none", CGROUP_MOUNT_PATH, "cgroup2", 0, NULL)) {
  82                 log_err("mount cgroup2");
  83                 return 1;
  84         }
  85
  86         if (mkdir(CGROUP_PATH, 0777) && errno != EEXIST) {
  87                 log_err("mkdir cgroup");
  88                 return 1;
  89         }
  90
  91         cg2 = open(CGROUP_PATH, O_RDONLY);
  92         if (cg2 < 0) {
  93                 log_err("opening target cgroup");
  94                 goto cleanup_cgroup_err;
  95         }
  96
  97         if (bpf_update_elem(map_fd[0], &idx, &cg2, BPF_ANY)) {
  98                 log_err("Adding target cgroup to map");
  99                 goto cleanup_cgroup_err;
 100         }
 101         if (join_cgroup("/mnt/my-cgroup")) {
 102                 log_err("Leaving target cgroup");
 103                 goto cleanup_cgroup_err;
 104         }
 105
 106         /*
 107          * The installed helper program catched the sync call, and should
 108          * write it to the map.
 109          */
 110
 111         sync();
 112         bpf_lookup_elem(map_fd[1], &idx, &remote_pid);
 113
 114         if (local_pid != remote_pid) {
 115                 fprintf(stderr,
 116                         "BPF Helper didn't write correct PID to map, but: %d\n",
 117                         remote_pid);
 118                 goto leave_cgroup_err;
 119         }
 120
 121         /* Verify the negative scenario; leave the cgroup */
 122         if (join_cgroup(CGROUP_MOUNT_PATH))
 123                 goto leave_cgroup_err;
 124
 125         remote_pid = 0;
 126         bpf_update_elem(map_fd[1], &idx, &remote_pid, BPF_ANY);
 127
 128         sync();
 129         bpf_lookup_elem(map_fd[1], &idx, &remote_pid);
 130
 131         if (local_pid == remote_pid) {
 132                 fprintf(stderr, "BPF cgroup negative test did not work\n");
 133                 goto cleanup_cgroup_err;
 134         }
 135
 136         rmdir(CGROUP_PATH);
 137         return 0;
 138
 139         /* Error condition, cleanup */
 140 leave_cgroup_err:
 141         join_cgroup(CGROUP_MOUNT_PATH);
 142 cleanup_cgroup_err:
 143         rmdir(CGROUP_PATH);
 144         return 1;
 145 }