DF-5081

mpu401_init/mpu401_uninit free the kobj without kobj_delete: parent mpu class reference never dropped, compiled kobj_ops pinned forever (unbounded refs++ on reattach)

Summary

kobj_init takes a class ref that only kobj_delete drops, but both free sites use bare kfree - refs never reaches 0, the ~2KB compiled ops table is pinned, and every attach/detach cycle grows refs. Bounded one-time leak + permanent refcount imbalance; hardware-gated (no emu10kx/cmi/emu10k1 on guest). kobj_delete fix.

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Severity: Info
Status: new
Bucket: Base system — drivers
Confidence: certain
Pass: 2 · GLM 5.3 second pass
CVSS 3.1: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L
CWE: CWE-401
File: sys/dev/sound/midi/mpu401.c
Lines: 177-205
Area: dev
Discovered: 2026-09-26
Updated: 2026-09-26

Team triage

untriaged

priority: — · owner: —

PoC verification

untested

Status: untested
Reproduced: no
Impact: bounded leak + refcount imbalance
Confidence: certain
Tested: 2026-09-26 21:53:27
Attempts: 0
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 root@dfbsd:/usr/src/sys/X86_64_GENERIC x86_64
Build cmd: n/a
Run cmd: n/a

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Fix verification

not_testable

Fix status: not_testable
Baseline reproduced: no
Patched reproduced: no
Confidence: certain
Tested: 2026-09-26 21:53:27
Runtime: —
Kernel: per-fix-DF-5081
fix.diff: findings/poc/DF-5081/fix.diff
Runner: df-bsd-reviewer

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PoC verification

Evidence pack

findings/poc/DF-5081 · 1 files

File	Type	Description	Size
verdict.json	file		916 B	view raw

Fix verification

not_testable

baseline no→ patch + rebuild →patched clean

per-fix-DF-5081

Confirmed kernel references

sys/dev/sound/midi/mpu401.c:177

Detail

Evidence (decisive lines)

static proof: mpu401.c:177 kobj_init vs bare kfree at :192/:205; subr_kobj.c:257-273

Verified recommended fix

kobj_delete instead of kfree at both sites

Verdict

untested (hardware-gated: no MPU-401 host on audit guest)