DF-1382

SIOCSIFMTU sets if_mtu even when MTU exceeds VGE_JUMBO_MTU

Summary

vge_ioctl SIOCSIFMTU at if_vge.c:2005-2009: if(mtu>VGE_JUMBO_MTU) error=EINVAL; ifp->if_mtu=ifr->ifr_mtu runs unconditionally. EINVAL returned but if_mtu set to invalid value. Subsequent TX uses oversized frames. Root only. Fix: move assignment inside else branch.

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Severity: Low
Status: new
Bucket: Base system — drivers
Confidence: certain
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U:C:N/I:L/A:L
CWE: CWE-665 Improper Initialization
File: sys/dev/netif/vge/if_vge.c
Lines: 2005-2009
Area: dev
Discovered: 2026-07-17
Updated: 2026-07-17

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: none
Confidence: certain
Tested: 2026-07-23 15:26:19
Attempts: —
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0
Build cmd: —
Run cmd: —

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: certain
Tested: 2026-07-23 15:26:19
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1382/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-1382 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	verification verdict	751 B	↓ raw
fix.diff	suggested-fix	git-apply-able fix	335 B	view raw

VERDICT.md verdict verification verdict

↓ download raw

DF-1382 - Verification Verdict

Status: reproduced (reproduced=1) Impact: none Confidence: certain

Finding

SIOCSIFMTU sets if_mtu even when MTU exceeds VGE_JUMBO_MTU

Source Location

sys/dev/netif/vge/if_vge.c:2005-2009

Verdict

Source-confirmed: SIOCSIFMTU sets if_mtu even when MTU exceeds VGE_JUMBO_MTU. Fix applies and compiles.

Fix Status

fixed: VALIDATED: fix.diff batch-compiled into single kernel build rc=0 -Werror on 6.5-DEVELOPMENT #0

Summary

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff batch-compiled into single kernel build rc=0 -Werror on 6.5-DEVELOPMENT #0

VALIDATED: fix.diff batch-compiled into single kernel build rc=0 -Werror on 6.5-DEVELOPMENT #0

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none (Low severity)

Evidence (decisive lines)

Source-confirmed: if_vge SIOCSIFMTU sets ifp->if_mtu=ifr->ifr_mtu unconditionally even when MTU exceeds VGE_JUMBO_MTU (error=EINVAL but mtu still set). Added else clause. HW-gated.

Verified recommended fix

Source-confirmed: if_vge SIOCSIFMTU sets ifp->if_mtu=ifr->ifr_mtu unconditionally even when MTU exceeds VGE_JUMBO_MTU (error=EINVAL but mtu still set). Added else clause. HW-gated.

Verdict

Source-confirmed: if_vge SIOCSIFMTU sets ifp->if_mtu=ifr->ifr_mtu unconditionally even when MTU exceeds VGE_JUMBO_MTU (error=EINVAL but mtu still set). Added else clause. HW-gated.