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

UBDescription

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
17.04i

int-division-by-zero

int-modulo-by-zero

Fully checked
CodeSonar
4.5p1
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

Klocwork
2017
DBZ.CONST
DBZ.CONST.CALL
DBZ.GENERAL
DBZ.ITERATOR

LDRA tool suite
9.7.1

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

Partially implemented
Parasoft C/C++test9.5BD-PB-ZEROFully implemented
Parasoft Insure++

Runtime detection
Polyspace Bug FinderR2016a

Integer division by zero, Tainted division operand, Tainted modulo operand

Dividing integer number by zero

Division / operands from an unsecure source

Remainder % operands are from an unsecure source

PRQA QA-C
9.3

2830 (C)
2831 (D)
2832 (A)
2833 (S)
2834 (P)

Fully implemented
PRQA QA-C++
4.1
2831, 2832, 2833, 2834
SonarQube C/C++ Plugin
3.11
S3518

Related Vulnerabilities

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

Related Guidelines

Bibliography

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



6 Comments

  1. Add compliant solutions demonstrating the use of signals in Linux and structured exception handling in Windows?

  2. Another division and modulo nuance that might be worth including is their ability to return negative numbers. This is probably obvious for division, but it can be surprising sometimes when (-10 % 1024) evaluates to -10. One possible concern would be in code for hash tables that takes a user malleable signed index.

  3. INT32 already has the NCCE/CCE pairs mentioned here. (although INT32 is strictly about signed integers.)

  4. I don't think the "stupid" NCE adds anything, and in fact, it recreates the problem you were trying to fix in having a noncompliant example that violates multiple rules. 

    1. I added the 'stupid' NCCE b/c it is more likely to occur in the real world. Normally I am uncomfortable with NCCEs that violate multiple rules, but I feel less uncomfortable than usual here because we already have an NCCE (the 2nd one) that violates this rule but no others.
      I considered adding this 'stupid' NCCE to INT32-C but felt that that rule was long enough already.

      1. Yeah, no one does any checking in the real world, but based on our examples, they can figure out this is wrong.  I'm going to remove.