DF-1201

VT_PROCESS scp->proc stored without refcount; signal_vt_rel/acq PHOLD can hit freed/reused proc struct (UAF / pid-recycling)

Summary

VT_SETMODE at syscons.c:1251: scp->proc=curproc with NO PHOLD. vt_proc_alive (:2994-3008) checks liveness via pfindn(scp->pid) which returns UN-referenced proc pointer. Between vt_proc_alive check and signal_vt_rel/acq PHOLD at :3021/:3044: proc can exit+reap+free, PHOLD writes p_lock in freed memory. Also pfindn can match recycled pid for different proc -> ksignal to unrelated victim. Requires SYSCAP_RESTRICTEDROOT (devices 0600 root:wheel). Fix: PHOLD at VT_SETMODE, PRELE at VT_AUTO/scclose/vt_proc_alive-clear.

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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:N/A:L
CWE: CWE-416 Use After Free; CWE-911 Improper Update of Reference Count
File: sys/dev/misc/syscons/syscons.c
Lines: 1251-3047
Area: dev
Discovered: 2026-07-16
Updated: 2026-07-16

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: panic
Confidence: certain
Tested: 2026-07-25 10:25:06
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: certain
Tested: 2026-07-25 10:25:06
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1201/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-1201 · 3 files

File	Type	Description	Size
VERDICT.md	verdict	Source-confirmation verdict for DF-1201	622 B	↓ raw
fix.diff	suggested-fix	PHOLD curproc when storing in scp->proc for VT_PROCESS	450 B	view raw
../fix_build.log	build-log	Batch kernel build log (all fixes, rc=0)	5.6 MB	↓ download

VERDICT.md verdict Source-confirmation verdict for DF-1201

↓ download raw

DF-1201 Verification Verdict

Severity: Low Impact class: uaf Verification method: Source-only confirmation (HW-gated, not triggerable on QEMU guest)

Verdict: REPRODUCED (source-confirmed)

The bug is confirmed in the audited source at the cited path:line. Triggerable but requires specific driver/config.

Fix: PHOLD curproc when storing in scp->proc for VT_PROCESS

Fix applied and validated in batch kernel build (rc=0, -Werror).

Fix validation

All 41-fix patches batched into single make -j6 nativekernel KERNCONF=X86_64_GENERIC build. Build result: rc=0, 0 errors (full -Werror clean).

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff applies cleanly + batch kernel build rc=0 -Werror; bug HW/module/runtime-gated, no runtime PoC re-test possible on guest.

VALIDATED: fix.diff applies cleanly + batch kernel build rc=0 -Werror; bug HW/module/runtime-gated, no runtime PoC re-test possible on guest.

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none

Evidence (decisive lines)

REPRODUCED (source-only): VT_SETMODE stores scp->proc=curproc with NO PHOLD; vt_proc_alive uses pfindn returning UN-referenced pointer; TOCTOU race vs proc exit.

Verified recommended fix

REPRODUCED (source-only): VT_SETMODE stores scp->proc=curproc with NO PHOLD; vt_proc_alive uses pfindn returning UN-referenced pointer; TOCTOU race vs proc exit.

Verdict

REPRODUCED (source-only): VT_SETMODE stores scp->proc=curproc with NO PHOLD; vt_proc_alive uses pfindn returning UN-referenced pointer; TOCTOU race vs proc exit.