DF-0392

Fragment overlap trim uses non-8-aligned shifts for last-fragment overlaps: inconsistent reassembly metadata

Summary

pf_reassemble overlap trim(:412-413,434-436): updates ip_off via (precut>>3) and (aftercut>>3). Non-final fragments guaranteed 8-byte aligned (checked :943). LAST fragment (MF=0) ip_len need not be 8-aligned -> precut/aftercut non-aligned -> >>3 truncation produces incorrect ip_off inconsistent with actual m_adj byte trim. Subtle payload corruption or normalization bypass. Not memory safety: all lengths bounded by IP_MAXPACKET checks.

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Severity: Low
Status: new
Bucket: Base system — network stack
Confidence: likely
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
CWE: CWE-197
File: sys/net/pf/pf_norm.c
Lines: 412-436
Area: net
Discovered: 2026-07-01
Updated: 2026-07-01

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: none
Confidence: likely
Tested: 2026-07-23 04:51:44
Attempts: 1
Runtime: —
Code hash: 25f9d1062003a9f4
Guest: DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 x86_64
Build cmd: n/a (source-only verification)
Run cmd: n/a (source-only verification)

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: likely
Tested: 2026-07-23 04:51:44
Runtime: —
Kernel: 6.5-DEVELOPMENT #0 (combined-fix build, rc=0 -Werror, Thu Jul 23 04:36:20 UTC 2026)
fix.diff: findings/poc/DF-0392/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0392 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	750 B	↓ raw
fix.diff	suggested-fix	fix for logic bug	377 B	view raw

VERDICT.md verdict source verification verdict

↓ download raw

DF-0392 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: logic

Impact: none

Source file: sys/net/pf/pf_norm.c

Mechanism

CONFIRMED: pf_reassemble overlap trim uses (precut>>3) for last fragment (MF=0) which need not be 8-aligned. Truncation produces incorrect ip_off. Fix: round precut down to 8-byte boundary.

Fix

See fix.diff for the git-apply-able patch.

Build validation

Combined kernel build with all 70 Low-severity fixes: rc=0, -Werror. All fixes compile cleanly in X86_64_GENERIC kernel configuration.

Guest: DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff compiles cleanly in combined kernel build (rc=0, -Werror). Source trace confirms bug at sys/net/pf/pf_norm.c:412.

Combined build: 70 fix.diffs applied to /usr/src, nativekernel KERNCONF=X86_64_GENERIC rc=0 -Werror. All fixes compile.

↓ fix.diff6.5-DEVELOPMENT #0 (combined-fix build, rc=0 -Werror, Thu Jul 23 04:36:20 UTC 2026)

Confirmed kernel references

Detail

Exploit chain

none (non-corruption Low severity finding; source-only confirmation)

Evidence (decisive lines)

Source-traced at sys/net/pf/pf_norm.c:412. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0392. No PoC binary (source-only verification).

Verified recommended fix

Round precut down to 8-byte boundary before >>3. Matches finding proposal.

Verdict

CONFIRMED source-only: overlap trim (precut>>3) incorrect for non-8-aligned last fragment.