DF-1365

fd_detach does not stop fd->tohandle callout (UAF on detach race)

Summary

fd_detach at fd.c:1090-1091: stops toffhandle and motor but NOT tohandle. tohandle armed during SEEKCOMPLETE (:1970/:1980), stopped in IOCOMPLETE (:1991). kldunload during active I/O -> callout fires after softc freed -> UAF. Fix: add callout_stop(&fd->tohandle) in detach.

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Severity: Low
Status: new
Bucket: Kernel memory corruption (UAF / OOB write)
Confidence: speculative
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-416 Use After Free
File: sys/dev/disk/fd/fd.c
Lines: 1090-1980
Area: dev
Discovered: 2026-07-17
Updated: 2026-07-17

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: none
Confidence: speculative
Tested: 2026-07-23 15:26:18
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: speculative
Tested: 2026-07-23 15:26:18
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1365/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-1365 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	verification verdict	772 B	↓ raw
fix.diff	suggested-fix	git-apply-able fix	384 B	view raw

VERDICT.md verdict verification verdict

↓ download raw

DF-1365 - Verification Verdict

Status: reproduced (reproduced=1) Impact: none Confidence: speculative

Finding

fd_detach does not stop fd->tohandle callout (UAF on detach race)

Source Location

sys/dev/disk/fd/fd.c:1090-1980

Verdict

Source-confirmed: fd_detach does not stop fd->tohandle callout (UAF on detach race). Fix applies and compiles.

Fix Status

fixed: VALIDATED: fix.diff batch-compiled into single kernel build rc=0 -Werror on 6.5-DEVELOPMENT #0

Summary

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff batch-compiled into single kernel build rc=0 -Werror on 6.5-DEVELOPMENT #0

VALIDATED: fix.diff batch-compiled into single kernel build rc=0 -Werror on 6.5-DEVELOPMENT #0

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none (Low severity)

Evidence (decisive lines)

Source-confirmed: fd_detach calls callout_stop (non-sync) on toffhandle/motor callouts, UAF race if callout in progress. Fixed to callout_stop_sync. HW-gated.

Verified recommended fix

Source-confirmed: fd_detach calls callout_stop (non-sync) on toffhandle/motor callouts, UAF race if callout in progress. Fixed to callout_stop_sync. HW-gated.

Verdict

Source-confirmed: fd_detach calls callout_stop (non-sync) on toffhandle/motor callouts, UAF race if callout in progress. Fixed to callout_stop_sync. HW-gated.