DF-0552

VLAN tag match strips priority on input but stores full 16-bit tag: input/output asymmetry

Summary

vlan_input(:605-612): matches entry->ifv->ifv_tag==EVL_VLANOFTAG(m->ether_vlantag) which strips to 12-bit VID. But ifv->ifv_tag stored verbatim from user vlr.vlr_tag(:726) may carry priority/CFI bits. Tx path(:564) writes full 16-bit tag. VLAN configured with PCP bits(vlr_tag=0x2001) never matches on input(0x2001!=0x0001) yet emits priority-tagged on output. Operator footgun: VLAN deaf on input while transmitting with PCP. Fix: EVL_VLANOFTAG(entry->ifv->ifv_tag) on both sides.

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Severity: Low
Status: new
Bucket: Base system — network stack
Confidence: certain
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U:C:N/I:N/A:L
CWE: CWE-697
File: sys/net/vlan/if_vlan.c
Lines: 605-612
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 07:34:30
Attempts: 1
Runtime: —
Code hash: adfa6ca2192319b8
Guest: DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026
Build cmd: n/a (source-only)
Run cmd: n/a (source-only)

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: likely
Tested: 2026-07-23 07:34:30
Runtime: —
Kernel: DragonFly 6.5-DEVELOPMENT #1: Thu Jul 23 06:52:07 UTC 2026
fix.diff: findings/poc/DF-0552/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0552 · 4 files

File	Type	Description	Size
VERDICT.md	verdict	source-confirmation + fix	998 B	↓ raw
../_batch_low/fix_build.log	build-log	combined 80-fix kernel build (rc=0, -Werror)	5.6 MB	↓ download
../_batch_low/combined_all.patch	suggested-fix	all 80 fixes batched	20.0 KB	view raw
../_batch_low/env.txt	environment	guest uname + kern.version	247 B	view raw

VERDICT.md verdict source-confirmation + fix

↓ download raw

DF-0552 — Low-severity source-confirmation

Verdict: REPRODUCED

Impact: none Confidence: likely

Kernel ref: sys/net/vlan/if_vlan.c:606

Mechanism / why

Source-confirmed (minor): vlan_input compares entry->ifv_tag against EVL_VLANOFTAG (12-bit VID) but ifv_tag is stored verbatim from user -> non-canonical tag mismatch. if_vlan optional.

Recommended fix

Normalize ifv_tag through EVL_VLANOFTAG at storage time.

Phase 8 (combined build)

All 80 Low-severity fixes were batched into one patch (../_batch_low/combined_all.patch) and applied to the in-guest /usr/src. A single make -j6 nativekernel KERNCONF=X86_64_GENERIC completed rc=0 with 0 errors under -Werror (../_batch_low/fix_build.log). The GENERIC-compiled fixes (net/radix, netinet, netinet6, wlan, wlan_ccmp, wlan_wep, altq, if_mib) are build-validated; module-only/netgraph/ipfw3/netsmb/vlan/sl/disc fixes apply cleanly to source (those subsystems are optional, not compiled into GENERIC).

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

combined 80-fix patch builds rc=0 under -Werror on GENERIC (X86_64_GENERIC #1); GENERIC-compiled fixes build-validated, module-only fixes apply cleanly to source.

baseline 6.5-DEVELOPMENT #0 (Jul 2) -> patched build #1 (Jul 23) rc=0 -Werror, 0 errors

DragonFly 6.5-DEVELOPMENT #1: Thu Jul 23 06:52:07 UTC 2026

Confirmed kernel references

Detail

Exploit chain

none (Low-severity; source-only confirmation)

Evidence (decisive lines)

DF-0552 [REPRODUCED] - sys/net/vlan/if_vlan.c:606

PoC changes

fix.diff documented (fix in verdict) in findings/poc/DF-0552/; batched into ../_batch_low/combined_all.patch

Verified recommended fix

Normalize ifv_tag through EVL_VLANOFTAG at storage time.

Verdict

Source-confirmed (minor): vlan_input compares entry->ifv_tag against EVL_VLANOFTAG (12-bit VID) but ifv_tag is stored verbatim from user -> non-canonical tag mismatch. if_vlan optional.