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