DF-1570

xa_close returns holding xdisk_lk and releases the wrong lock on race paths

Summary

xdisk.c:767 xa_close acquires xdisk_lk. 769-770 sc==NULL returns ENXIO WITHOUT releasing xdisk_lk -> permanent lock leak. 771-773 sc->terminating does lockmgr(&sc->lk, LK_RELEASE) releasing WRONG lock (never acquired sc->lk) AND returns without releasing xdisk_lk. Contrast xa_open (704-714) correctly releases xdisk_lk on all error paths. Once leaked every xa_open/xa_close/xdisk_attach/xaio_rcvdmsg blocks forever in lockmgr. Trigger: race where si_drv1 NULL or terminating at xa_close entry; currently unreachable but latent footgun. Fix: release xdisk_lk on both error paths.

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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:L
CWE: CWE-664 Improper Control of a Resource Through its Lifetime
File: sys/dev/disk/xdisk/xdisk.c
Lines: 767-793
Area: dev
Discovered: 2026-07-18
Updated: 2026-07-18

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: dos
Confidence: likely
Tested: 2026-07-23 17:00:05
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 17:00:05
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1570/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-1570 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	506 B	view raw
VERDICT.md	verdict	source-confirmation analysis	706 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-1570 VERDICT

Verdict: REPRODUCED (source-confirmed)

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

Mechanism: xdisk.c:767 xa_close acquires xdisk_lk. 769-770 sc==NULL returns ENXIO WITHOUT releasing xdisk_lk -> permanent lock leak. 771-773 sc->terminating does lockmgr(&sc->lk, LK_RELEASE) releasing WRONG lock

Citation: sys/dev/disk/xdisk/xdisk.c:767-793

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: xa_close returns holding xdisk_lk and releases wrong lock sc->lk (xdisk.c:767-773)

Verified recommended fix

Source-confirmed: xa_close returns holding xdisk_lk and releases wrong lock sc->lk (xdisk.c:767-773)

Verdict

Source-confirmed: xa_close returns holding xdisk_lk and releases wrong lock sc->lk (xdisk.c:767-773)