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.

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	1.0 KB	↓ raw
build.sh	build-script	N/A (source-only)	65 B	view raw
run.sh	run-script	N/A (source-only)	89 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 status (batch validation)

Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest make -j6 nativekernel KERNCONF=X86_64_GENERIC completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.

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