1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Seccomp BPF example using a macro-based generator.
4 *
5 * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
6 * Author: Will Drewry <wad@chromium.org>
7 *
8 * The code may be used by anyone for any purpose,
9 * and can serve as a starting point for developing
10 * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
11 */
12
13#include <linux/filter.h>
14#include <linux/seccomp.h>
15#include <linux/unistd.h>
16#include <stdio.h>
17#include <string.h>
18#include <sys/prctl.h>
19#include <unistd.h>
20
21#include "bpf-helper.h"
22
23#ifndef PR_SET_NO_NEW_PRIVS
24#define PR_SET_NO_NEW_PRIVS 38
25#endif
26
27int main(int argc, char **argv)
28{
29	struct bpf_labels l = {
30		.count = 0,
31	};
32	static const char msg1[] = "Please type something: ";
33	static const char msg2[] = "You typed: ";
34	char buf[256];
35	struct sock_filter filter[] = {
36		/* TODO: LOAD_SYSCALL_NR(arch) and enforce an arch */
37		LOAD_SYSCALL_NR,
38		SYSCALL(__NR_exit, ALLOW),
39		SYSCALL(__NR_exit_group, ALLOW),
40		SYSCALL(__NR_write, JUMP(&l, write_fd)),
41		SYSCALL(__NR_read, JUMP(&l, read)),
42		DENY,  /* Don't passthrough into a label */
43
44		LABEL(&l, read),
45		ARG(0),
46		JNE(STDIN_FILENO, DENY),
47		ARG(1),
48		JNE((unsigned long)buf, DENY),
49		ARG(2),
50		JGE(sizeof(buf), DENY),
51		ALLOW,
52
53		LABEL(&l, write_fd),
54		ARG(0),
55		JEQ(STDOUT_FILENO, JUMP(&l, write_buf)),
56		JEQ(STDERR_FILENO, JUMP(&l, write_buf)),
57		DENY,
58
59		LABEL(&l, write_buf),
60		ARG(1),
61		JEQ((unsigned long)msg1, JUMP(&l, msg1_len)),
62		JEQ((unsigned long)msg2, JUMP(&l, msg2_len)),
63		JEQ((unsigned long)buf, JUMP(&l, buf_len)),
64		DENY,
65
66		LABEL(&l, msg1_len),
67		ARG(2),
68		JLT(sizeof(msg1), ALLOW),
69		DENY,
70
71		LABEL(&l, msg2_len),
72		ARG(2),
73		JLT(sizeof(msg2), ALLOW),
74		DENY,
75
76		LABEL(&l, buf_len),
77		ARG(2),
78		JLT(sizeof(buf), ALLOW),
79		DENY,
80	};
81	struct sock_fprog prog = {
82		.filter = filter,
83		.len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
84	};
85	ssize_t bytes;
86	bpf_resolve_jumps(&l, filter, sizeof(filter)/sizeof(*filter));
87
88	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
89		perror("prctl(NO_NEW_PRIVS)");
90		return 1;
91	}
92
93	if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
94		perror("prctl(SECCOMP)");
95		return 1;
96	}
97	syscall(__NR_write, STDOUT_FILENO, msg1, strlen(msg1));
98	bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf)-1);
99	bytes = (bytes > 0 ? bytes : 0);
100	syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2));
101	syscall(__NR_write, STDERR_FILENO, buf, bytes);
102	/* Now get killed */
103	syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2)+2);
104	return 0;
105}
106