// 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;
}