Page History

...

The valid() function does not guarantee validity (it only identifies null pointers and pointers to functions as invalid), but it can be used to catch a substantial number of problems that might otherwise go undetected.

...

Noncompliant 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 can still be invalid, causing the function to corrupt memory or terminate abnormally.

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

Compliant Solution

By using the valid() function defined above, the function is less likely to dereference an invalid pointer or write to memory that is outside the bounds of a valid object.

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

Compliant Solution (assert)

Because invalid pointers are often indicative of a bug defect in the program, the assert() macro can be used to terminate immediately if an invalid pointer is discovered (see MSC11-AC. Incorporate diagnostic tests using assertions).

#include <assert.h>

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

Risk Assessment

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

...

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

\[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\] Section 6.3.2.3, "Pointers"
\[[Jack 07|AA. C References#Jack 07]\]
\[[van Sprundel 06|AA. C References#van Sprundel 06]\]

...