Detecting Pointer Subtraction

Pointer Subtraction Detection

Detection Workflow

1. Identify pointer subtractions: Find all pointer subtraction operations, locate size calculations using pointers, identify pointer arithmetic for bounds, map memory operations using pointer math
2. Analyze pointer relationships: Verify pointers are from same array, check pointer alignment, assess pointer validity, verify pointer types
3. Check result usage: Trace subtraction result to usage, check for integer underflow, assess impact on memory operations, verify bounds checking logic
4. Assess security impact: Can underflow cause overflow? Can it bypass security checks? What's the potential impact? Is it exploitable?

Key Patterns

• Size calculation errors: using pointer subtraction for size calculation, subtracting pointers from different arrays, incorrect pointer arithmetic for buffer sizes, size calculation without alignment consideration
• Integer underflow: pointer subtraction causing underflow, unsigned integer wraparound, negative results treated as large positive, size calculations going negative
• Bounds checking issues: using pointer subtraction for bounds checks, incorrect comparison results, off-by-one in pointer arithmetic, misaligned pointer operations
• Memory operations: memcpy with pointer-subtracted size, malloc with pointer-subtracted size, loop bounds from pointer subtraction, array indexing from pointer subtraction

Output Format

Report with: id, type, subtype, severity, confidence, location, vulnerability, subtraction_operation, start_pointer, end_pointer, result_type, risk, exploitable, attack_scenario, impact, mitigation.

Severity Guidelines

• HIGH: Pointer subtraction causing buffer overflow
• MEDIUM: Pointer subtraction causing logic errors
• LOW: Minor pointer arithmetic issues

See Also

• patterns.md - Detailed detection patterns and exploitation scenarios
• examples.md - Example analysis cases and code samples
• references.md - CWE references and mitigation strategies