DF-1601

ks_kbds slave list torn down without kbd_token in kbdmux_term, racing KBDIO_UNLOADING callback (UAF / list corruption)

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.

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Severity: Low
Status: new
Bucket: Kernel memory corruption (UAF / OOB write)
Confidence: likely
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U:C:N/I:L/A:H
CWE: CWE-362 Race Condition
File: sys/dev/misc/kbdmux/kbdmux.c
Lines: 452-1232
Area: dev
Discovered: 2026-07-18
Updated: 2026-07-18

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: panic
Confidence: likely
Tested: 2026-07-23 17:00:07
Attempts: —
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0
Build cmd: —
Run cmd: —

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: likely
Tested: 2026-07-23 17:00:07
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1601/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

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	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-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 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

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