Understanding Integer Overflows: Causes, Consequences, and Preventions, Slides of Software Engineering

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Integer Overflows

What is an integer overflow?

“[T]he condition that occurs when a calculation produces a result that is greater in magnitude than that which a given register or storage location can store or represent.”

• Wikipedia - Arithmetic overflow

http://en.wikipedia.org/wiki/Arithmetic_overflow

C/C++ Data Types

Source: http://hubpages.com/hub/Data-Types-in-C-Language

Casting Operations

Unsigned int to Larger unsigned int

Best case (no worries)

Casting Operations

Unsigned int to Same-Size signed int

Bit pattern is preserved

New value depends on original sign bit

Casting Operations

Downcast

Truncates original value

Data loss may occur

Value may become negative

Implicit Casting

Operators may cause implicit casting

Operators (+,-,*,/,%,&,|,^,&&,||,!) follow these rules:

If either operand is an unsigned long, both are upcast to an

unsigned long.

Otherwise, both operands are upcast to an int and the result is

an int.

Source: 19 Deadly Sins. Howard, Leblanc, Viega [2005]

Security Concerns

Integer overflows may lead to buffer overruns

Memory allocation

Array indexing

Unexpected control flow

Crash