Arithmetic operation with NULL pointer

Arithmetic operation performed on NULL pointer

Description

This defect occurs when an arithmetic operation involves a pointer whose value is NULL.

Risk

Performing pointer arithmetic on a null pointer and dereferencing the resulting pointer is undefined behavior. In most implementations, the dereference can cause your program to crash.

Fix

Check a pointer for NULL before arithmetic operations on the pointer.

If the issue occurs despite an earlier check for NULL, look for intermediate events between the check and the subsequent dereference. Often the result details show a sequence of events that led to the defect. You can implement the fix on any event in the sequence. If the result details do not show the event history, you can trace back using right-click options in the source code and see previous related events. See also Interpret Bug Finder Results in Polyspace Desktop User Interface.

See examples of fixes below.

Examples

Arithmetic Operation with NULL Pointer Error

#include<stdlib.h>

int Check_Next_Value(int *loc, int val) 
 {
  int *ptr = loc, found = 0; 
  
  if (ptr==NULL)
   { 
      ptr++; 
      /* Defect: NULL pointer shifted */

      if (*ptr==val) found=1;
   } 
   
  return(found);    
 }

When ptr is a NULL pointer, the code enters the if statement body. Therefore, a NULL pointer is shifted in the statement ptr++.

Correction — Avoid NULL Pointer Arithmetic

One possible correction is to perform the arithmetic operation when ptr is not NULL.

#include<stdlib.h>

int Check_Next_Value(int *loc, int val) 
 {
  int *ptr = loc, found = 0; 
  
  /* Fix: Perform operation when ptr is not NULL */
  if (ptr!=NULL)
   { 
      ptr++;

      if (*ptr==val) found=1;
   }
   
  return(found);    
 }

Result Information

Group: Static memory

Language: C | C++

Default: Off

Command-Line Syntax: NULL_PTR_ARITH

Impact: Low