DF-1929

NULL-pointer dereference in acpi_battery_find_dev when battery devclass is absent

Summary

acpi_battery_find_dev L349-350 batt_dc=devclass_find(battery); maxunit=devclass_get_maxunit(batt_dc). devclass_get_maxunit subr_bus.c:1047-1050 dereferences dc unconditionally. If batt_dc==NULL (kldunload acpi_cmbat after hooks registered) immediate kernel panic. Sibling acpi_battery_get_units L88 and acpi_battery_get_battinfo L132 correctly NULL-check; clear oversight. Reachable from acpi_battery_ioctl L379-380 unit!=ACPI_BATTERY_ALL_UNITS. Hooks stay registered permanently (acpi_battery_remove L76 no-op). Local unpriv /dev/acpi arg.unit=0 ioctl ACPIIO_BATT_GET_BIF. Requires post-kldunload state. Fix: if(batt_dc==NULL)return(NULL) mirror siblings.

Discussion (0)

No comments yet.

Severity: Low
Status: new
Bucket: Base system — drivers
Confidence: likely
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U:C:N/I:N/A:H
CWE: CWE-476
File: sys/dev/acpica/acpi_battery.c
Lines: 349-380
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: likely
Tested: 2026-07-23 17:00:16
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: likely
Tested: 2026-07-23 17:00:16
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1929/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-1929 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	413 B	view raw
VERDICT.md	verdict	source-confirmation analysis	709 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-1929 VERDICT

Verdict: REPRODUCED (source-confirmed)

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

Mechanism: acpi_battery_find_dev L349-350 batt_dc=devclass_find(battery); maxunit=devclass_get_maxunit(batt_dc). devclass_get_maxunit subr_bus.c:1047-1050 dereferences dc unconditionally. If batt_dc==NULL (kldun

Citation: sys/dev/acpica/acpi_battery.c:349-380

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: devclass_get_maxunit(NULL) panic when battery devclass gone (acpi_battery.c:349-380)

Verified recommended fix

Source-confirmed: devclass_get_maxunit(NULL) panic when battery devclass gone (acpi_battery.c:349-380)

Verdict

Source-confirmed: devclass_get_maxunit(NULL) panic when battery devclass gone (acpi_battery.c:349-380)