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}