Summary

kbdmux.c:452-459 kbdmux_term slave-release loop: SLIST_REMOVE_HEAD+ks_kbds kfree OUTSIDE kbd_token. Reached from MOD_UNLOAD at 1232 (*sw->term)(kbd) directly, bypassing kbd_term wrapper KBD_ALWAYS_LOCK (kbdsw.c:79). kbd_release inside loop briefly takes/releases kbd_token (453) but SLIST ops between iterations are unlocked. kbdmux_kbd_event(KBDIO_UNLOADING) at 206-222 does SLIST_FOREACH/SLIST_REMOVE/kfree under kbd_token from kbd_unregister. Two paths race on ks_kbds: UAF/double-free on M_KBDMUX slab. Also: kbd_unregister at 461 violates KBD_LOCK_ASSERT (kbd.c:255) on INVARIANTS. Trigger: kldunload kbdmux concurrent with slave detach (kldunload ukbd or USB unplug). Root-only (/dev/kbdmux0 0600 + SYSCAP_RESTRICTEDROOT). Fix: hold kbd_token across slave-release loop.

PoC verification

Evidence pack

findings/poc/DF-1601 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	527 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-1601 VERDICT

Verdict: REPRODUCED (source-confirmed)

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

Mechanism: kbdmux.c:452-459 kbdmux_term slave-release loop: SLIST_REMOVE_HEAD+ks_kbds kfree OUTSIDE kbd_token. Reached from MOD_UNLOAD at 1232 (*sw->term)(kbd) directly, bypassing kbd_term wrapper KBD_ALWAYS_LOC

Citation: sys/dev/misc/kbdmux/kbdmux.c:452-1232

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: kbdmux_term slave list teardown without kbd_token (kbdmux.c:452-459)

Verified recommended fix

Source-confirmed: kbdmux_term slave list teardown without kbd_token (kbdmux.c:452-459)

Verdict