1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
| // SPDX-License-Identifier: GPL-2.0
| /*
| * Seccomp BPF example using a macro-based generator.
| *
| * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
| * Author: Will Drewry <wad@chromium.org>
| *
| * The code may be used by anyone for any purpose,
| * and can serve as a starting point for developing
| * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
| */
|
| #include <linux/filter.h>
| #include <linux/seccomp.h>
| #include <linux/unistd.h>
| #include <stdio.h>
| #include <string.h>
| #include <sys/prctl.h>
| #include <unistd.h>
|
| #include "bpf-helper.h"
|
| #ifndef PR_SET_NO_NEW_PRIVS
| #define PR_SET_NO_NEW_PRIVS 38
| #endif
|
| int main(int argc, char **argv)
| {
| struct bpf_labels l = {
| .count = 0,
| };
| static const char msg1[] = "Please type something: ";
| static const char msg2[] = "You typed: ";
| char buf[256];
| struct sock_filter filter[] = {
| /* TODO: LOAD_SYSCALL_NR(arch) and enforce an arch */
| LOAD_SYSCALL_NR,
| SYSCALL(__NR_exit, ALLOW),
| SYSCALL(__NR_exit_group, ALLOW),
| SYSCALL(__NR_write, JUMP(&l, write_fd)),
| SYSCALL(__NR_read, JUMP(&l, read)),
| DENY, /* Don't passthrough into a label */
|
| LABEL(&l, read),
| ARG(0),
| JNE(STDIN_FILENO, DENY),
| ARG(1),
| JNE((unsigned long)buf, DENY),
| ARG(2),
| JGE(sizeof(buf), DENY),
| ALLOW,
|
| LABEL(&l, write_fd),
| ARG(0),
| JEQ(STDOUT_FILENO, JUMP(&l, write_buf)),
| JEQ(STDERR_FILENO, JUMP(&l, write_buf)),
| DENY,
|
| LABEL(&l, write_buf),
| ARG(1),
| JEQ((unsigned long)msg1, JUMP(&l, msg1_len)),
| JEQ((unsigned long)msg2, JUMP(&l, msg2_len)),
| JEQ((unsigned long)buf, JUMP(&l, buf_len)),
| DENY,
|
| LABEL(&l, msg1_len),
| ARG(2),
| JLT(sizeof(msg1), ALLOW),
| DENY,
|
| LABEL(&l, msg2_len),
| ARG(2),
| JLT(sizeof(msg2), ALLOW),
| DENY,
|
| LABEL(&l, buf_len),
| ARG(2),
| JLT(sizeof(buf), ALLOW),
| DENY,
| };
| struct sock_fprog prog = {
| .filter = filter,
| .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
| };
| ssize_t bytes;
| bpf_resolve_jumps(&l, filter, sizeof(filter)/sizeof(*filter));
|
| if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
| perror("prctl(NO_NEW_PRIVS)");
| return 1;
| }
|
| if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
| perror("prctl(SECCOMP)");
| return 1;
| }
| syscall(__NR_write, STDOUT_FILENO, msg1, strlen(msg1));
| bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf)-1);
| bytes = (bytes > 0 ? bytes : 0);
| syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2));
| syscall(__NR_write, STDERR_FILENO, buf, bytes);
| /* Now get killed */
| syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2)+2);
| return 0;
| }
|
|
