detecting-pointer-subtraction

Testing & Quality

Detects unsafe pointer subtraction operations that can lead to incorrect size calculations and integer underflow. Use when analyzing pointer arithmetic, size calculations, or investigating buffer sizing issues.

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I want to install this Agent Skill for this project in Codex.

Source SKILL.md: https://github.com/majiayu000/claude-skill-registry/blob/HEAD/skills/data/detecting-pointer-subtraction/SKILL.md

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Pointer Subtraction Detection

Detection Workflow

Identify pointer subtractions: Find all pointer subtraction operations, locate size calculations using pointers, identify pointer arithmetic for bounds, map memory operations using pointer math
Analyze pointer relationships: Verify pointers are from same array, check pointer alignment, assess pointer validity, verify pointer types
Check result usage: Trace subtraction result to usage, check for integer underflow, assess impact on memory operations, verify bounds checking logic
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