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.

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	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-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 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: 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