30b0bce884f93f89c56481469d82649d509dc4e9
[muen/linux.git] / 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 }