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Eliminated Guideline

This guideline has been labeled void and designated for future elimination from the C++ Secure Coding Practices. It has not been erased yet in case it contains information that might still be useful.


Ensuring that arrays are used securely is almost entirely the responsibility of the programmer. One of the principle problems with arrays is determining their size.

Non-Compliant Code Example

This non-compliant code example shows a function insert_in_table() that takes two int arguments, pos and value, both of which can be influenced by data originating from untrusted sources. The function uses a global variable table to determine if storage has been allocated for an array of 100 integer elements and allocates the memory if it has not already been allocated. The function then performs a range check to ensure that pos does not exceed the upper bound of the array but fails to check the lower bound for table. Because pos has been declared as a (signed) int, this parameter can easily assume a negative value, resulting in a write outside the bounds of the memory referenced by table.

Compliant Solution 1

In this compliant solution, the parameter pos is now an unsigned integer type, preventing passing of negative arguments.

Compliant Solution 2

Specialized function templates can be used to define functions that accept an array of a generic type T of size n. The compiler can perform template argument deduction for function templates to properly deduce both the type and size. This compliant solution defines a function template for a function clear() that takes a template parameter array[] of T elements and an actual length parameter of type size_t. This is not particularly useful yet, as we have already seen that passing an array with an explicit size parameter is a common (but error prone) idiom. However, you can also define a specialization of the function template that includes a template parameter n of type size_t in addition to the original type parameter. The inline function clear() has one parameter: an array of type T elements of fixed length n.

The function template and specialized function template can be used in a straightforward manner. This example declares an array of 12 integers named int_array and invokes the clear() function passing int_array as an argument. The compiler matches this invocation to inline void clear(T (&array)[n]) because this definition most closely matches the actual argument type of array of int. The compiler deduces that the type T is int and that n is 12, separating the size n from the pointer to the array of int before invoking the function template for clear(). This use of specialized function templates guarantees that the clear() function has the correct array size.

Risk Assessment

Out-of-range indices can allow an attacker to execute arbitrary code with the privileges of the vulnerable process.

Rule

Severity

Likelihood

Remediation Cost

Priority

Level

ARR30-C

3 (high)

3 (likely)

1 (high)

P9

L2

References

[ISO/IEC 14882-2003] Section 8.3.4 Arrays
[Dewhurst 05] Item 6 Array Formal Arguments


            

1 Comment

  1. This looks complete to me... removing tag