CERT C: Rule INT32-C

Integer overflow occurs when an operation on integer variables can result in values that cannot be represented by the result data type. The data type of a variable determines the number of bytes allocated for the variable storage and constrains the range of allowed values.

The exact storage allocation for different floating point types depends on your processor. See Target processor type (-target). W

Integer overflows on signed integers result in undefined behavior.

The fix depends on the root cause of the defect. Often the result details show a sequence of events that led to the defect. Use this event list to determine how the variables in the overflowing computation acquire their current values. 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.

You can fix the defect by:

To avoid overflows in general, try one of these techniques:

See examples of fixes below.

If you do not want to fix the issue, add comments to your result or code to avoid another review. See:

#include <limits.h>

int plusplus(void) {

    int var = INT_MAX;
    var++;              //Noncompliant
    return var;
}

In the third statement of this function, the variable var is increased by one. But the value of var is the maximum integer value, so an int cannot represent one plus the maximum integer value.

One possible correction is to change data types. Store the result of the operation in a larger data type (Note that on a 32-bit machine, int and long has the same size). In this example, on a 32-bit machine, by returning a long long instead of an int, the overflow error is fixed.

#include <limits.h>

long long plusplus(void) {

    long long lvar = INT_MAX;
    lvar++;
    return lvar;
}

Tainted division operand detects division operations where one or both of the integer operands is from an unsecure source.

These risks can be used to execute arbitrary code. This code is usually outside the scope of a program's implicit security policy.

Before performing the division, validate the values of the operands. Check for denominators of 0 or -1, and numerators of the minimum integer value.

#include <limits.h>
#include <stdio.h>

extern void print_int(int);

int taintedintdivision(void) {
    long num, denum;
    scanf("%lf %lf", &num, &denum);
    int r =  num/denum;  //Noncompliant
    print_int(r);
    return r;
}

This example function divides two argument variables, then prints and returns the result. The argument values are unknown and can cause division by zero or integer overflow.

One possible correction is to check the values of the numerator and denominator before performing the division.

#include <limits.h>
#include <stdio.h>

extern void print_long(long);

int taintedintdivision(void) {
    long num, denum;
    scanf("%lf %lf", &num, &denum);
    long res= 0;
    if (denum!=0 && !(num==INT_MIN && denum==-1)) {
        res = num/denum;
    }
    print_long(res);
    return res;
}

Tainted modulo operand checks the operands of remainder % operations. Bug Finder flags modulo operations with one or more tainted operands.

These risks can be exploited by attackers to gain access to your program or the target in general.

Before performing the modulo operation, validate the values of the operands. Check the second operand for values of 0 and -1. Check both operands for negative values.

#include<stdio.h>
extern void print_int(int);

int taintedintmod(void) {
	int userden;
	scanf("%d",&userden);
    int rem =  128%userden;  //Noncompliant
    print_int(rem);
    return rem;
}

In this example, the function performs a modulo operation by using a user input. The user input is not checked before calculating the remainder for values that can crash the program, such as 0 and -1.

One possible correction is to check the values of the operands before performing the modulo operation. In this corrected example, the modulo operation continues only if the second operand is greater than zero.

#include<stdio.h>
extern void print_int(int);

int taintedintmod(void) {
	int userden;
	scanf("%d",&userden);
	int rem = 0;
    if (userden > 0) { 
        rem = 128 % userden; 
    }
    print_int(rem);
    return rem;
}