针对isdn_net_newslave函数strcpy缓冲区溢出的提权漏洞利用咨询

Hey there! Since you're a cybersecurity newbie diving into kernel buffer overflow exploitation on Linux 3.18.19, let's break down your questions with practical, actionable details tailored to that specific kernel version and vulnerability.

First, let's demystify ASLR (Address Space Layout Randomization) for kernel exploitation:

• Kernel ASLR randomizes the base addresses of critical kernel regions like the kernel stack, heap, loaded modules, and core kernel text every reboot. This breaks hardcoded addresses in your exploit—if you hardcode a shellcode address or return address, it'll be invalid after the next boot because ASLR shifted everything.
• To exploit this without turning off ASLR, focus on address leakage and relative offsets:
  • Hunt for information leaks in the ISDN subsystem or other kernel interfaces. For example, /proc/kallsyms might expose some symbol addresses (if the kernel config allows it), or you could trigger a separate leak via an uninitialized memory exposure bug in the same subsystem.
  • Once you leak one symbol's address (like printk or the base of the ISDN module), you can compute the offset to your target gadgets or shellcode location.
• Another approach is Return-Oriented Programming (ROP). Kernel ROP uses small code snippets (gadgets) from existing kernel code. Since gadgets are at fixed offsets relative to each other, even with ASLR, you can chain them to perform actions (like spawning a root shell) without needing absolute addresses—you just need one leaked address to anchor the chain.

The newname parameter is user-controlled, passed from user space to the isdn_net_newslave kernel function. Here's how to take control of it:

• First, map the user-kernel interaction: isdn_net_newslave is typically triggered via an ioctl system call from user-space tools like isdnctrl. Look up the specific IOCTL command in headers like <linux/isdn.h> and the data structure it expects.
• Write a custom C program that calls this ioctl directly. In your program, construct a malicious newname string that's longer than the kernel-side buffer it's being copied into (since strcpy doesn't check length).
• Ensure your payload lives in a user-space memory region the kernel can access (use copy_from_user-safe addresses—avoid non-page-aligned or restricted memory). When you send the ioctl, the kernel will pull your malicious newname into its buffer via strcpy, triggering the overflow.

To nail this exploit step-by-step:

1. Set up a debug environment:
   • Compile the Linux 3.18.19 kernel with debug symbols (enable CONFIG_DEBUG_INFO in make menuconfig) and disable strict protections temporarily (like KASLR) to test your exploit first, then re-enable KASLR for the final ASLR-aware version.
   • Use QEMU to run the kernel, and attach GDB to debug the kernel in real-time.
2. Analyze the vulnerable code:
   • Locate the strcpy call in isdn_net_newslave (line 2639). Check the size of the destination buffer (e.g., char slave_buf[64];). Calculate exactly how many bytes you need to write to overflow the buffer and overwrite the function's return address.
   • Use GDB to set a breakpoint at the strcpy call, then inspect the stack to find the offset from the buffer to the return address.
3. Construct your payload:
   • For kernel exploits, avoid user-space shellcode if SMAP/SMEP are enabled (3.18 may have these—they block kernel execution of user-space memory). Instead, build a ROP chain that calls commit_creds(prepare_kernel_cred(0)) to get root privileges, then jumps back to user space with a shell.
   • If you're working with ASLR, add a step to leak a kernel symbol address first, then adjust your ROP gadget addresses using the leaked offset.
4. Validate & iterate:
   • Test your exploit in the debug environment first to ensure the overflow correctly overwrites the return address and executes your payload. Then move to a non-debug environment with ASLR enabled, using your address-leaking logic to adapt to dynamic addresses.

内容的提问来源于stack exchange，提问作者user7241550