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Sometimes null is returned intentionally Functions may intentionally return null to account for zero available instances. This practice can lead to vulnerabilities when the client code does not correctly handle the null return case.

Noncompliant Code Example

The erroneous behavior is caused due to getStock results form getStock() returning null while main() forgets to add in a check for such a value. This In this noncompliant code example shows how , the check for item != null condition is missing from the if condition in function main().

#include <stdio.h>

typedef struct 
{
  int item[20];
  int length;
} Inventory;

int * getStock(Inventory iv);

int main (int argc, char* argv[])
void) {
  Inventory iv;
  intsize_t i;
  int * item;

  iv.length = 0;
  item = getStock(iv);

  for (i = 0; i < 20; i++) {
    if (item[i] == 1) {
      printf("Almost out of stock of item: %d", i);
    }
  }
  return 0;
}

int * getStock(Inventory iv) 
{
  if (iv.length == 0) {
    return NULL;
  }
  else {
    return iv.item;
  }
}

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#include <stdio.h>

typedef struct 
{
  int item[20];
  int length;
} Inventory;

int * getStock(Inventory iv);

int main (int argc, char* argv[])
(void) {
  Inventory iv;
  intsize_t i;
  int * item;

  iv.length = 0;
  item = getStock(iv);

  for (i = 0; i < 20; i++) {
    if (item[i] == 1) {
      printf("Almost out of stock of item: %d", i);
    }
  }
  return 0;
}

int * getStock(Inventory iv) 
{
  return iv.item;
}

Risk Assessment

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Other Languages

This rule guideline appears in the Java Secure Coding Standard as MET03-J. For methods that return an array or collection prefer returning an empty array or collection over a null value.

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

References

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