Integer Overflow Vulnerability In Gguf_fread_str()

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Integer Overflow Vulnerability in gguf_fread_str(): A Critical Security Risk

Introduction

As part of our ongoing security audit, we have identified a critical integer overflow vulnerability in the gguf_fread_str() function that could lead to memory allocation issues and potential security risks. This vulnerability arises from the direct reading of an untrusted input size value into the p->n variable, followed by its use in a calloc() call without any validation or overflow checks. In this article, we will delve into the mechanism of the vulnerability, provide relevant code snippets, and suggest actions to mitigate this critical security risk.

Mechanism of Vulnerability

The gguf_fread_str() function reads a size value p->n directly from an untrusted input file. This value is then used in calloc(p->n + 1, 1) without any validation or overflow checks. If an attacker provides a malicious input where p->n is SIZE_MAX, the addition of 1 will cause an integer overflow, resulting in calloc(0, 1). This could lead to either a zero-byte allocation, causing subsequent buffer overflow when writing data, or excessive memory allocation if the implementation handles the overflow differently.

Step-by-Step Vulnerability Explanation

  1. Untrusted Input: The gguf_fread_str() function reads an untrusted input size value p->n from a file.
  2. Direct Use: The value p->n is directly used in calloc(p->n + 1, 1) without any validation or overflow checks.
  3. Integer Overflow: If p->n is SIZE_MAX, the addition of 1 causes an integer overflow, resulting in calloc(0, 1).
  4. Potential Consequences: This could lead to either a zero-byte allocation or excessive memory allocation.

Relevant Code Snippets

The following code snippets demonstrate the vulnerable gguf_fread_str() function and the gguf_fread_el() function used to read the untrusted input size value.

ggml.c - gguf_fread_str()

static bool gguf_fread_str(FILE * file, struct gguf_str * p, size_t * offset) {
    p->n    = 0;
    p->data = NULL;

    bool ok = true;

    ok = ok && gguf_fread_el(file, &p->n,    sizeof(p->n), offset); p->data = calloc(p->n + 1, 1);
    ok = ok && gguf_fread_el(file,  p->data, p->n,         offset);

    return ok;
}

ggml.c - gguf_fread_el()

static bool gguf_fread_el(FILE * file, void * dst, size_t size, size_t * offset) {
    const size_t n = fread(dst, 1, size, file);
    *offset += n;
    return n == size;
}

Vulnerability Analysis

A thorough analysis of the vulnerability reveals the following key points:

  1. Input Source: The vulnerability originates from reading untrusted input via gguf_fread_el() into p->n.
  2. Missing Validation: No bounds checking is performed on p->n before using it in memory allocation3. Arithmetic Risk: The expression p->n + 1 in calloc() is vulnerable to integer overflow.
  3. Direct Propagation: The tainted value flows directly from input to allocation without sanitization.
  4. Unconditional Flow: All execution paths reach the vulnerable allocation without intermediate constraints.

Suggested Action

To mitigate this critical security risk, the code should be modified to include proper validation and overflow checks:

  1. Bounds Checking: Add bounds checking before allocation to prevent integer overflow:
if (p->n > SIZE_MAX - 1) {
    return false;  // Handle error case
}
  1. Safe Arithmetic Operations: Use safe arithmetic operations to prevent integer overflow:
size_t alloc_size;
if (__builtin_add_overflow(p->n, 1, &alloc_size)) {
    return false;  // Handle overflow case
}
p->data = calloc(alloc_size, 1);
  1. Maximum Size Limit: Consider implementing a maximum size limit for the input to prevent excessive memory allocation.

By implementing these suggested actions, the gguf_fread_str() function can be made more secure and resistant to integer overflow vulnerabilities.

Conclusion

The gguf_fread_str() function contains a critical integer overflow vulnerability that could lead to memory allocation issues and potential security risks. This vulnerability arises from the direct reading of an untrusted input size value into the p->n variable, followed by its use in a calloc() call without any validation or overflow checks. By understanding the mechanism of the vulnerability and implementing proper validation and overflow checks, developers can mitigate this critical security risk and ensure the security and reliability of their code.
Integer Overflow Vulnerability in gguf_fread_str(): A Critical Security Risk - Q&A

Introduction

In our previous article, we discussed the critical integer overflow vulnerability in the gguf_fread_str() function that could lead to memory allocation issues and potential security risks. In this article, we will address some frequently asked questions (FAQs) related to this vulnerability and provide additional information to help developers understand and mitigate this security risk.

Q&A

Q1: What is an integer overflow vulnerability?

A1: An integer overflow vulnerability occurs when a program attempts to store a value in a variable that is too large to be represented by the variable's data type. This can cause the program to produce incorrect results or crash.

Q2: How does the gguf_fread_str() function contain an integer overflow vulnerability?

A2: The gguf_fread_str() function reads an untrusted input size value p->n from a file and uses it in a calloc() call without any validation or overflow checks. If the input size value is SIZE_MAX, the addition of 1 will cause an integer overflow, resulting in calloc(0, 1).

Q3: What are the potential consequences of this vulnerability?

A3: The potential consequences of this vulnerability include:

  • Zero-byte allocation, causing subsequent buffer overflow when writing data
  • Excessive memory allocation if the implementation handles the overflow differently
  • Denial of service or potentially more severe security issues depending on how the allocated memory is used in subsequent operations

Q4: How can I identify if my code contains a similar vulnerability?

A4: To identify if your code contains a similar vulnerability, follow these steps:

  1. Review your code for functions that read untrusted input values and use them in memory allocation calls.
  2. Check if the input values are validated or checked for overflow before being used in memory allocation calls.
  3. Use tools such as static analysis or dynamic analysis to identify potential vulnerabilities in your code.

Q5: How can I mitigate this vulnerability?

A5: To mitigate this vulnerability, follow these steps:

  1. Add bounds checking before allocation to prevent integer overflow:

if (p->n > SIZE_MAX - 1) { return false; // Handle error case }

2.  Use safe arithmetic operations to prevent integer overflow:
    ```cpp
size_t alloc_size;
if (__builtin_add_overflow(p->n, 1, &alloc_size)) {
    return false;  // Handle overflow case
}
p->data = calloc(alloc_size, 1);
  1. Consider implementing a maximum size limit for the input to prevent excessive memory allocation.

Q6: Can I use a different memory allocation function to avoid this vulnerability?

A6: While using a different memory allocation function may avoid this specific vulnerability, it is essential to ensure that the new function does not introduce other security risks. Always validate and check input values before using them in memory allocation calls.

Q7: How can I prevent similar vulnerabilities in the future?

A7: To prevent similar vulnerabilities in the future, follow these best practices:

  1. Validate and check input values before using them in memory allocation calls.
  2. Use arithmetic operations to prevent integer overflow.
  3. Implement bounds checking before allocation to prevent integer overflow.
  4. Consider implementing a maximum size limit for the input to prevent excessive memory allocation.

By following these best practices and understanding the mechanism of the vulnerability, developers can mitigate this critical security risk and ensure the security and reliability of their code.

Conclusion

The gguf_fread_str() function contains a critical integer overflow vulnerability that could lead to memory allocation issues and potential security risks. By understanding the mechanism of the vulnerability and implementing proper validation and overflow checks, developers can mitigate this critical security risk and ensure the security and reliability of their code.