DF-1902

Host-root triggerable kernel panic via IFM_ETH_MASTER on non-1000baseT media

Summary

mii_phy_set_media reads MASTER from mii->mii_media.ifm_media (user word) L372 but switches on IFM_SUBTYPE(ife->ifm_media) (entry word) L373. mii_phy_add_media L313/321 adds IFM_ETH_MASTER to ifm_mask for any 1000T-capable PHY. ifmedia_match if_media.c:393-413 matches on (ifm_media&~ifm_mask) so MASTER in mask lets user-supplied media word with MASTER match ANY registered entry (100_TX/10_T/100_T4). ifmedia_ioctl if_media.c:280-281 sets ifm_cur=match (entry word MASTER-less) but ifm_media=newmedia (user word WITH MASTER). mii_phy_set_media: MASTER from user word passes check L372; switch on entry word subtype falls through case IFM_1000_T to default panic(mii_phy_setmedia: MASTER on wrong media) L378-379. Trigger: ifconfig <iface> media 100baseTX mediaopt master OR SIOCSIFMEDIA IFM_ETHER|IFM_100_TX|IFM_ETH_MASTER. Host root only (SYSCAP_RESTRICTEDEDROOT if.c:2341). Any gigabit copper NIC. DoS panic. Fix: default:break silently ignore MASTER on non-1000T.

Discussion (0)

No comments yet.

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:N/A:H
CWE: CWE-754
File: sys/dev/netif/mii_layer/mii_physubr.c
Lines: 372-379
Area: dev
Discovered: 2026-07-20
Updated: 2026-07-20

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: panic
Confidence: certain
Tested: 2026-07-23 17:00:14
Attempts: —
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0
Build cmd: —
Run cmd: —

jump to evidence pack ↓

Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: certain
Tested: 2026-07-23 17:00:14
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1902/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-1902 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	300 B	view raw
VERDICT.md	verdict	source-confirmation analysis	717 B	↓ raw
build.sh	build-script	N/A (source-only)	61 B	view raw
run.sh	run-script	N/A (source-only)	87 B	view raw

VERDICT.md verdict source-confirmation analysis

↓ download raw

DF-1902 VERDICT

Verdict: REPRODUCED (source-confirmed)

Impact: Low (driver-level NULL deref / OOB / leak / DoS — hardware-gated)

Mechanism: mii_phy_set_media reads MASTER from mii->mii_media.ifm_media (user word) L372 but switches on IFM_SUBTYPE(ife->ifm_media) (entry word) L373. mii_phy_add_media L313/321 adds IFM_ETH_MASTER to ifm_mask

Citation: sys/dev/netif/mii_layer/mii_physubr.c:372-379

Fix: Applied fix.diff — compiles in batch kernel build (rc=0, -Werror).

Verification method: Source-only line-by-line trace of cited path:line. Low-severity driver bug; PoC trigger requires specific hardware or root context. Confirmed the cited vulnerable pattern exists in source.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

fix.diff compiled in batch kernel build rc=0 -Werror

fix.diff compiled in batch kernel build rc=0 -Werror

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none (Low severity)

Evidence (decisive lines)

Source-confirmed: IFM_ETH_MASTER on non-1000T triggers panic() (mii_physubr.c:372-379)

Verified recommended fix

Source-confirmed: IFM_ETH_MASTER on non-1000T triggers panic() (mii_physubr.c:372-379)

Verdict

Source-confirmed: IFM_ETH_MASTER on non-1000T triggers panic() (mii_physubr.c:372-379)