# HoneyMesh eBPF Security Audit Report

**Scope**: `bpf/main.c` and related map usage (XDP program)

**Method**: Static review only (no verifier logs, fuzzing, or runtime tracing).

**Date**: 2026-02-23

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## 1. Summary
The eBPF/XDP program is now significantly hardened. The highest‑risk issues (IPv4 option evasion, scan‑map races, whitelist gaps, and ringbuf pressure) were remediated. IPv6 telemetry includes source/destination addresses and transport ports with bounded extension‑header traversal (bound = 8). Sampling is configurable via `security.event_sample_n` to tune overhead under load.

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## 2. Findings (Current)

### Low — IPv6 extension header traversal is bounded
**File**: `bpf/main.c`

**Issue**: IPv6 extension headers are parsed with a bounded loop (max 8 headers). Extremely long or unusual chains may still not resolve transport ports.

**Impact**: Reduced visibility in rare cases; no kernel memory safety risk.

**Recommendation**: Increase the bound only if needed; keep bounded for verifier safety.

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### Low — Resource exhaustion potential at very high PPS
**File**: `bpf/main.c`

**Issue**: Even with sampling, ringbuf traffic under extreme PPS can still add CPU overhead.

**Impact**: Telemetry drops and CPU load (DoS risk), not memory corruption.

**Recommendation**: Tune `security.event_sample_n` upward under stress.

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## 3. Remediated Issues

### ✅ IPv4 options evasion (ihl ignored)
**Fixed**: IPv4 header length now uses `ip->ihl * 4` with bounds validation before parsing TCP/UDP.

### ✅ Map update races in scan tracking
**Fixed**: `scan_counter` is now `BPF_MAP_TYPE_LRU_PERCPU_HASH`.

### ✅ IPv6 whitelist parity
**Fixed**: Added `whitelist_cidr_v6` LPM trie and Go‑side sync of IPv6 CIDRs.

### ✅ Ringbuf DoS pressure
**Fixed**: Allow‑event emission is sampled; sampling is configurable with `security.event_sample_n`.

### ✅ IPv6 telemetry
**Fixed**: IPv6 event emission includes `src_ip6`, `dst_ip6`, and transport port with bounded extension‑header traversal.

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## 4. Kernel Safety Assessment
**Verifier bypass risk**: No obvious bypass patterns found.

**Memory safety**: Packet data access is bounds‑checked. IPv4 header length is validated prior to L4 access.

**Map safety**: No use‑after‑free or invalid map pointer usage observed.

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## 5. Compliance / Licensing
The eBPF program declares `GPL` license as required by the kernel for helper usage. Project code is MIT‑licensed.

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## 6. Recommendations (Optional Hardening)
1. Capture verifier logs and include in audit appendix.
2. Fuzz malformed packets (IPv4 options, IPv6 EH chains).
3. Load test at 1M+ PPS to observe ringbuf pressure.

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## 7. Files Reviewed
- `bpf/main.c`
- `bpf_x86_bpfel.go` (generated)
- `bpf_x86_bpfel.o` (generated)

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## 8. Limitations
This audit is a static analysis. Enterprise certification should include:
- Verifier log inspection
- Fuzzing of packet parsing
- Runtime stress testing

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## 9. Conclusion
HoneyMesh’s eBPF/XDP code is robust against common kernel‑level risks. Remaining issues are visibility/performance tradeoffs rather than kernel‑safety defects.