1 /* Copyright (c) 2017 Facebook
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 #include <linux/bpf.h>
9 #include <linux/version.h>
10 #include <bpf/bpf_helpers.h>
11
12 SEC("cgroup/dev")
13 int bpf_prog1(struct bpf_cgroup_dev_ctx *ctx)
14 {
15 short type = ctx->access_type & 0xFFFF;
16 #ifdef DEBUG
17 short access = ctx->access_type >> 16;
18 char fmt[] = " %d:%d \n";
19
20 switch (type) {
21 case BPF_DEVCG_DEV_BLOCK:
22 fmt[0] = 'b';
23 break;
24 case BPF_DEVCG_DEV_CHAR:
25 fmt[0] = 'c';
26 break;
27 default:
28 fmt[0] = '?';
29 break;
30 }
31
32 if (access & BPF_DEVCG_ACC_READ)
33 fmt[8] = 'r';
34
35 if (access & BPF_DEVCG_ACC_WRITE)
36 fmt[9] = 'w';
37
38 if (access & BPF_DEVCG_ACC_MKNOD)
39 fmt[10] = 'm';
40
41 bpf_trace_printk(fmt, sizeof(fmt), ctx->major, ctx->minor);
42 #endif
43
44 /* Allow access to /dev/zero and /dev/random.
45 * Forbid everything else.
46 */
47 if (ctx->major != 1 || type != BPF_DEVCG_DEV_CHAR)
48 return 0;
49
50 switch (ctx->minor) {
51 case 5: /* 1:5 /dev/zero */
52 case 9: /* 1:9 /dev/urandom */
53 return 1;
54 }
55
56 return 0;
57 }
58
59 char _license[] SEC("license") = "GPL";
60
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.