Sargun Dhillon | 9e6e60e | 2016-08-12 08:57:04 -0700 | [diff] [blame] | 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 | } |