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void func(unsigned int ui_a, unsigned int ui_b) {
  unsigned int usum = ui_a + ui_b;
  if (usum < ui_a) {
    /* Handle error */
  }
  /* ... */
}

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Compliant Solution (C23, Checked Integers)

This compliant solution uses the new-to-C23 checked integer arithmetic to safely perform integer addition:

#include <stdckdint.h>

void func(unsigned int ui_a, unsigned int ui_b) {
  unsigned int usum;
  if (ckd_add(&usum, ui_a, ui_b)) {
    /* Handle error */
  }
  /* ... */
}

Subtraction

Subtraction is between two operands of arithmetic type, two pointers to qualified or unqualified versions of compatible object types, or a pointer to an object type and an integer type. This rule applies only to subtraction between two operands of arithmetic type. (See ARR36-

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Subtraction

Subtraction is between two operands of arithmetic type, two pointers to qualified or unqualified versions of compatible object types, or a pointer to an object type and an integer type. This rule applies only to subtraction between two operands of arithmetic type. (See ARR36-C. Do not subtract or compare two pointers that do not refer to the same array, ARR37-C. Do not add or subtract an integer to a pointer to a non-array object, and ARR30-C. Do not form or use out-of-bounds pointers or array subscripts for information about pointer subtraction.)

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void func(unsigned int ui_a, unsigned int ui_b) {
  unsigned int udiff = ui_a - ui_b;
  if (udiff > ui_a) {
    /* Handle error */
  }
  /* ... */
}

Compliant Solution (C23, Checked Integers)

This compliant solution uses the new-to-C23 checked integer arithmetic to safely perform integer subtraction:

#include <stdckdint.h>

void func(unsigned int ui_a, unsigned int ui_b) {
  unsigned int udiff;
  if (ckd_sub(&udiff, ui_a, ui_b)) {
    /* Handle error */
  }
  /* ... */
}

Multiplication

Multiplication is between two operands of arithmetic type.

Noncompliant Code Example

The Mozilla Foundation Security Advisory 2007-01 describes a heap buffer overflow vulnerability in the Mozilla Scalable Vector Graphics (SVG) viewer resulting from an unsigned integer wrap during the multiplication of the signed int value pen->num_vertices and the size_t value sizeof(cairo_pen_vertex_t) [VU#551436]. The signed int operand is converted to size_t prior to the multiplication operation so that the multiplication takes place between two size_t integers, which are unsigned. (See INT02-C.

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Understand integer conversion rules.)

pen->num_vertices = _cairo_pen_vertices_needed(
  gstate->tolerance, radius, &gstate->ctm
);
pen->vertices = malloc(
  pen->num_vertices * 

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Multiplication

Multiplication is between two operands of arithmetic type.

Noncompliant Code Example

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sizeof(cairo_pen_vertex_t)
);

The unsigned integer wrap can result in allocating memory of insufficient size.

Compliant Solution

This compliant solution tests the operands of the multiplication to guarantee that there is no unsigned integer wrap: [VU#551436]. The signed int operand is converted to size_t prior to the multiplication operation so that the multiplication takes place between two size_t integers, which are unsigned. (See INT02-C. Understand integer conversion rules.)

pen->num_vertices = _cairo_pen_vertices_needed(
  gstate->tolerance, radius, &gstate->ctm
);_needed(
  gstate->tolerance, radius, &gstate->ctm
);

if (pen->num_vertices > SIZE_MAX / sizeof(cairo_pen_vertex_t)) {
  /* Handle error */
}
pen->vertices = malloc(
  pen->num_vertices * sizeof(cairo_pen_vertex_t)
);

The unsigned integer wrap can result in allocating memory of insufficient size.

Compliant Solution (C23, Checked Integers)

This compliant solution tests the operands of the multiplication to guarantee that there is no unsigned integer wrapuses the new-to-C23 checked integer arithmetic to safely perform integer multiplication:

#include <stdckdint.h>

/* ... */

pen->num_vertices = _cairo_pen_vertices_needed(
  gstate->tolerance, radius, &gstate->ctm
);

size_t product;
if (ckd_mul(&product, pen->num_vertices > SIZE_MAX /, sizeof(cairo_pen_vertex_t))) {
  /* Handle error */
}

pen->vertices = malloc(
  pen->num_vertices * sizeof(cairo_pen_vertex_t)
);
 malloc(product);

Exceptions

INT30-C-EX1: Unsigned integers can exhibit modulo behavior (wrapping) when necessary for the proper execution of the program. It is recommended that the variable declaration be clearly commented as supporting modulo behavior and that each operation on that integer also be clearly commented as supporting modulo behavior.

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INT30-C-EX3. The left-shift operator takes two operands of integer type. Unsigned left shift << can exhibit modulo behavior (wrapping).  This exception is provided because of common usage, because this behavior is usually expected by the programmer, and because the behavior is well defined. For examples of usage of the left-shift operator, see INT34-C. Do not shift an expression by a negative number of bits or by greater than or equal to the number of bits that exist in the operand.

Risk Assessment

that exist in the operand.

Risk Assessment

Integer wrap can lead to buffer overflows and the execution of arbitrary code by an attacker. Note that this rule is not automatically repairable in contrast to INT32-C. Ensure that operations on signed integers do not result in overflow. This is because integer wrapping is occasionally intended (see INT30-C-EX1), and repairing such wrapping would turn correct code into code that spuriously signals wraparound errorsInteger wrap can lead to buffer overflows and the execution of arbitrary code by an attacker.

Automated Detection

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