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As you can see, the invalid() function is not perfect; it only identifies NULL pointers and pointers to functions as invalid.

Non-Compliant Code Example

This function increments the value pointed to by its argument. It also ensures that its argument is not a null pointer. But the pointer could still be invalid, thus causing the function to corrupt memory, or possibly terminate abnormally.

void incr(int *intptr) {
  if (intptr == NULL) {
    /* handle error */
  }
  *intptr++;
}

Compliant Solution

By using the invalid() function defined above, the function is less likely to modify memory outside its bounds.

void incr(int *intptr) {
  if (invalid( intptr)) {
    /* handle error */
  }
  *intptr++;
}

Compliant Solution (assert)

Since invalid pointers are often indicative of a bug in the program, one can use the assert() macro to terminate immediately if an invalid pointer is discovered.

#include <assert.h>

void incr(int *intptr) {
  assert(!invalid( intptr));
  *intptr++;
}

Risk Assessment

A pointer validation library can be used to identify, and thus, prevent the execution of vulnerable code

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