bpf-fancy.c

// 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;
}