CWE-781: Improper Address Validation in IOCTL with METHOD_NEITHER I/O Control Code

What is Improper Address Validation in IOCTL with METHOD_NEITHER I/O Control Code?

• Overview: Improper Address Validation in IOCTL with METHOD_NEITHER I/O Control Code occurs when software uses METHOD_NEITHER for I/O control without properly validating the addresses provided by users, allowing attackers to manipulate memory addresses maliciously.

• Exploitation Methods:

• Attackers can supply arbitrary memory addresses to the IOCTL, potentially leading to unauthorized memory access.
• Common attack patterns include buffer overflows and arbitrary code execution by directing execution flow to attacker-controlled code.

• Security Impact:

• Direct consequences include the ability for attackers to execute arbitrary code or cause a denial of service by crashing the system.
• Potential cascading effects include unauthorized access to sensitive information and system compromise.
• Business impact can involve data breaches, system downtime, and damage to reputation and customer trust.

• Prevention Guidelines:

• Specific code-level fixes include implementing rigorous validation checks on all user-supplied addresses.
• Security best practices involve using safer I/O control methods that inherently validate addresses, such as METHOD_BUFFERED or METHOD_IN_DIRECT.
• Recommended tools and frameworks include static and dynamic analysis tools to detect address validation issues, and adopting secure coding standards like CERT C guidelines.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: C, C++

Affected Technologies: Not specified

Vulnerable Code Example

// Vulnerable IOCTL handler using METHOD_NEITHER without proper address validation

#include <linux/uaccess.h>  // Required for memory validation functions
#include <linux/slab.h>     // For memory allocation

#define IOCTL_METHOD_NEITHER 0x222000

long ioctl_handler(struct file *file, unsigned int cmd, unsigned long arg) {
    void *user_buffer;

    switch (cmd) {
        case IOCTL_METHOD_NEITHER:
            // Directly using the user pointer without validation
            user_buffer = (void *)arg; 
            
            // Dangerous: Directly dereferencing user_buffer without checking
            printk(KERN_INFO "User buffer content: %s\n", (char *)user_buffer);
            break;
        default:
            return -EINVAL;
    }
    return 0;
}

Explanation of Vulnerability

In this vulnerable code example, the IOCTL handler directly uses a user-provided pointer (arg) without any validation. This can lead to serious security issues such as kernel crashes, data leaks, or privilege escalation if a malicious user provides an invalid or specially crafted pointer. The code directly dereferences the user pointer, which is dangerous as the pointer could point to invalid memory or even malicious code.

How to fix Improper Address Validation in IOCTL with METHOD_NEITHER I/O Control Code?

To fix this vulnerability, follow these best practices:

1. Validate User Pointers: Use access_ok() to ensure the user-provided pointer is valid and accessible.
2. Copy Data Safely: Use copy_from_user() and copy_to_user() to safely read from and write to user-space memory.
3. Limit Buffer Size: Always validate and limit the buffer size to prevent buffer overflows.
4. Check Return Values: Always check the return values of functions like copy_from_user() to ensure data was copied successfully.

Fixed Code Example

// Fixed IOCTL handler with proper address validation and safe memory operations

#include <linux/uaccess.h>  // Required for memory validation functions
#include <linux/slab.h>     // For memory allocation

#define IOCTL_METHOD_NEITHER 0x222000
#define BUFFER_SIZE 256  // Define a safe maximum buffer size

long ioctl_handler(struct file *file, unsigned int cmd, unsigned long arg) {
    char kernel_buffer[BUFFER_SIZE]; // Allocate a buffer on the stack

    switch (cmd) {
        case IOCTL_METHOD_NEITHER:
            // Validate the user pointer before using it
            if (!access_ok((void __user *)arg, BUFFER_SIZE)) {
                printk(KERN_WARNING "Invalid user buffer address\n");
                return -EFAULT;
            }
            
            // Safely copy data from user space to kernel space
            if (copy_from_user(kernel_buffer, (void __user *)arg, BUFFER_SIZE)) {
                printk(KERN_WARNING "Failed to copy data from user\n");
                return -EFAULT;
            }
            
            printk(KERN_INFO "User buffer content: %s\n", kernel_buffer);
            break;
        default:
            return -EINVAL;
    }
    return 0;
}

Explanation of Fix

In the fixed code example, the user pointer is validated using access_ok() to ensure it points to a valid and accessible user-space address. The copy_from_user() function is used to safely copy data from the user-space pointer to a kernel buffer, preventing direct dereferencing of potentially malicious user pointers. This approach maintains kernel memory safety and prevents unauthorized access or crashes caused by improper address validation. Additionally, the code uses a defined buffer size to prevent buffer overflows and checks return values to handle errors appropriately.