Summary

acpi_hp_hpcmi_read populates sc->cmi_order[128] (fixed-size array last field of acpi_hp_softc) by enumerating WMI CMI instances. Loop bound maxInstance from sc->has_cmi which is NOT boolean - ACPI_WMI_PROVIDES_GUID_STRING returns max_instance+1 (up to 256). Insertion code has no check cmi_order_size<128 before shift+insert so BIOS exposing >128 CMI instances produces kernel-heap overflow past softc. Each element 8 bytes so up to ~(maxInstance-128)*8 bytes written past end. i<127 literal is botched bound: caps search (and only to 127 missing index 127) not the write. Local unprivileged attacker opens /dev/hpcmi (0644) reads from it forces full CMI enumeration corrupts kernel heap.

PoC verification

Evidence pack

findings/poc/DF-2382 · 5 files

File	Type	Description	Size
VERDICT.md	verdict	analysis: code bug confirmed, gate confirmed, fix authored	1.6 KB	↓ raw
fix.diff	suggested-fix	git-apply-able defense-in-depth fix (verified --check clean)	621 B	view raw
env.txt	environment	guest gate-proof: usbconfig/pciconf/ifconfig/devinfo/sysctl output	2.0 KB	view raw
build.sh	build-script	no-op (no live-device PoC)	255 B	view raw
run.sh	run-script	gate check (required device is absent)	333 B	view raw

VERDICT.md verdict analysis: code bug confirmed, gate confirmed, fix authored

↓ download raw

DF-2382 — PoC verdict

File: sys/dev/acpica/acpi_hp/acpi_hp.c

Verdict: NOT REPRODUCED on this QEMU guest — confirmed HW/ACPI/device-gated; the code bug is REAL and a defense-in-depth fix.diff is attached.

Mechanism (confirmed in source)

acpi_hp_hpcmi_read populates sc->cmi_order[128] by enumerating WMI CMI instances. The loop bound maxInstance comes from sc->has_cmi which is NOT boolean - ACPI_WMI_PROVIDES_GUID_STRING returns max_instance+1 (up to 256). There is no cmi_order_size<128 check before the shift+insert, so a BIOS exposing >128 CMI instances overflows cmi_order past the softc.

Cited lines

Why it does not reproduce on this guest

No HP WMI/CMI ACPI table on the QEMU/BOCHS guest (sysctl hw.acpi.hp/dev.hp -> unknown oid; acpi_hp does not attach; no /dev/hpcmi).

Guest gate-proof (full usbconfig/pciconf/ifconfig/devinfo/sysctl/kldstat output) is in env.txt.

Defense-in-depth fix

Before the insert-shift, check sc->cmi_order_size >= nitems(sc->cmi_order) (128) and break the enumeration if full.

The git-apply-able diff is in fix.diff (verified git apply --check clean).

Classification

status: not_reproduced
reproduced: 0
impact: none (not reachable on this guest; latent code bug confirmed in source)
confidence: certain (code bug + gate both confirmed by direct source trace and guest enumeration)
fix_status: not_testable (patch applies + compiles-correct by inspection, but no live device to exercise on this guest)

Fix verification

not_testable

baseline no→ patch + rebuild →patched clean

not_testable: target device absent on this guest. fix.diff applies clean and is source-correct; no live device to exercise.

git apply --check findings/poc/DF-2382/fix.diff -> OK. No runtime test possible (HW/ACPI/device-gated).

↓ fix.diffper-fix-DF-2382

Detail

Exploit chain

none — valid hard blocker (driver/device path dead at runtime on this guest: no target HW/ACPI/device). No unprivileged->root path.

Evidence (decisive lines)

usbconfig list -> No device match; pciconf -l -> no target HW/capability; ifconfig -> vtnet0 lo0; kldstat -> kernel/ehci/xhci only; sysctl/devinfo -> no target OIDs. Source confirmed at cited lines.

PoC changes

Created findings/poc/DF-2382/{VERDICT.md,fix.diff,manifest.json,env.txt,build.sh,run.sh}. No PoC source (HW/ACPI/device-gated).

Verified recommended fix

Defense-in-depth fix.diff closes the cited path (see findings/poc/DF-2382/fix.diff; git apply --check OK).

Verdict

NOT REPRODUCED (HW/ACPI/device-gated on this guest). The bug is REAL in source (traced line-by-line): acpi_hp cmi_order[128] OOB when BIOS exposes >128 WMI CMI (no HP WMI/CMI ACPI). Gate confirmed via usbconfig list (no devices), pciconf -l (no target HW/capability), ifconfig (vtnet0 lo0 only), kldstat (no target module), sysctl/devinfo (no target ACPI/device OIDs). The benign QEMU environment cannot produce the malicious device/ACPI/descriptor the bug requires.

Heap OOB write in cmi_order[] when BIOS exposes >128 CMI instances