# INT33-C. Ensure that division and remainder operations do not result in divide-by-zero errors

The C Standard identifies the following condition under which division and remainder operations result in undefined behavior (UB):

 UB Description 45 The value of the second operand of the `/` or `%` operator is zero (6.5.5).

Ensure that division and remainder operations do not result in divide-by-zero errors.

## Division

The result of the `/` operator is the quotient from the division of the first arithmetic operand by the second arithmetic operand. Division operations are susceptible to divide-by-zero errors. Overflow can also occur during two's complement signed integer division when the dividend is equal to the minimum (most negative) value for the signed integer type and the divisor is equal to `−1.` (See INT32-C. Ensure that operations on signed integers do not result in overflow.)

### Noncompliant Code Example

This noncompliant code example prevents signed integer overflow in compliance with INT32-C. Ensure that operations on signed integers do not result in overflow but fails to prevent a divide-by-zero error during the division of the signed operands `s_a` and `s_b`:` `

```#include <limits.h>

void func(signed long s_a, signed long s_b) {
signed long result;
if ((s_a == LONG_MIN) && (s_b == -1)) {
/* Handle error */
} else {
result = s_a / s_b;
}
/* ... */
}```

### Compliant Solution

This compliant solution tests the division operation to guarantee there is no possibility of divide-by-zero errors or signed overflow:

```#include <limits.h>

void func(signed long s_a, signed long s_b) {
signed long result;
if ((s_b == 0) || ((s_a == LONG_MIN) && (s_b == -1))) {
/* Handle error */
} else {
result = s_a / s_b;
}
/* ... */
}```

## Remainder

The remainder operator provides the remainder when two operands of integer type are divided.

### Noncompliant Code Example

This noncompliant code example prevents signed integer overflow in compliance with INT32-C. Ensure that operations on signed integers do not result in overflow but fails to prevent a divide-by-zero error during the remainder operation on the signed operands `s_a` and `s_b`:

```#include <limits.h>

void func(signed long s_a, signed long s_b) {
signed long result;
if ((s_a == LONG_MIN) && (s_b == -1)) {
/* Handle error */
} else {
result = s_a % s_b;
}
/* ... */
}```

### Compliant Solution

This compliant solution tests the remainder operand to guarantee there is no possibility of a divide-by-zero error or an overflow error:

```#include <limits.h>

void func(signed long s_a, signed long s_b) {
signed long result;
if ((s_b == 0 ) || ((s_a == LONG_MIN) && (s_b == -1))) {
/* Handle error */
} else {
result = s_a % s_b;
}
/* ... */
}```

## Risk Assessment

A divide-by-zero error can result in abnormal program termination and denial of service.

Rule

Severity

Likelihood

Remediation Cost

Priority

Level

INT33-C

Low

Likely

Medium

P6

L2

### Automated Detection

Tool

Version

Checker

Description

Astrée
24.04

int-division-by-zero

int-modulo-by-zero

Fully checked
Axivion Bauhaus Suite

7.2.0

CertC-INT33
CodeSonar
8.1p0
LANG.ARITH.DIVZERO
LANG.ARITH.FDIVZERO
Division by zero
Float Division By Zero
Compass/ROSE

Can detect some violations of this rule (In particular, it ensures that all operations involving division or modulo are preceded by a check ensuring that the second operand is nonzero.)

Coverity
2017.07

DIVIDE_BY_ZERO

Fully implemented
Cppcheck
1.66
zerodiv
zerodivcond

Context sensitive analysis of division by zero
Not detected for division by struct member / array element / pointer data that is 0
Detected when there is unsafe division by variable before/after test if variable is zero

Helix QAC

2024.1

C2830

C++2830

DF2831, DF2832, DF2833

Klocwork
2024.1

DBZ.CONST
DBZ.CONST.CALL
DBZ.GENERAL
DBZ.ITERATOR
DBZ.ITERATOR.CALL

LDRA tool suite
9.7.1

43 D, 127 D, 248 S, 629 S, 80 X

Partially implemented
Parasoft C/C++test2023.1

CERT_C-INT33-a

Avoid division by zero
Parasoft Insure++

Runtime analysis
Polyspace Bug Finder

R2024a

CERT C: Rule INT33-C

Checks for:

• Integer division by zero
• Tainted division operand
• Tainted modulo operand

Rule fully covered.

SonarQube C/C++ Plugin
3.11
S3518
PVS-Studio

7.31

V609
TrustInSoft Analyzer

1.38

division_by_zero

Exhaustively verified (see one compliant and one non-compliant example).

### Related Vulnerabilities

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

## Related Guidelines

Key here (explains table format and definitions)

Taxonomy

Taxonomy item

Relationship

CERT CINT32-C. Ensure that operations on signed integers do not result in overflowPrior to 2018-01-12: CERT: Unspecified Relationship
CERT Oracle Secure Coding Standard for JavaNUM02-J. Ensure that division and remainder operations do not result in divide-by-zero errorsPrior to 2018-01-12: CERT: Unspecified Relationship
ISO/IEC TS 17961Integer division errors [diverr]Prior to 2018-01-12: CERT: Unspecified Relationship
CWE 2.11CWE-369, Divide By Zero2017-07-07: CERT: Exact

## CERT-CWE Mapping Notes

Key here for mapping notes

### CWE-682 and INT33-C

CWE-682 = Union( INT33-C, list) where list =

• Incorrect calculations that do not involve division by zero

## Bibliography

 [Seacord 2013b] Chapter 5, "Integer Security" [Warren 2002] Chapter 2, "Basics"