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.

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	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-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 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: 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