DF-0380

Non-atomic refcount --node->refs/--hook->refs under crit_enter only: cross-CPU UAF/double-free race

Summary

ng_unref(:473-484) decrements node->refs (plain int) via --node->refs under crit_enter/crit_exit only. crit_enter blocks local interrupts/IPIs but NOT other CPUs. Increment sites (ng_add_hook:724, ng_queue_data:1946, ng_queue_msg:1995) use plain ++ with at most crit. Two CPUs racing read-modify-write: refs=N both write N-1 (leak) or both reach <=0 and kfree twice (double-free->UAF). NG_NODE_REF macro uses atomic_add_int(netgraph.h:132) but ng_unref does not — inconsistent. Same for hook->refs(:687-694).

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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:L/UI:N/S:U/C:L/I:L/A:H
CWE: CWE-911
File: sys/netgraph/netgraph/ng_base.c
Lines: 473-484
Area: net
Discovered: 2026-07-01
Updated: 2026-07-01

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: dos
Confidence: likely
Tested: 2026-07-23 04:51:43
Attempts: 1
Runtime: —
Code hash: 9a9ac0d5cceaf7e8
Guest: DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 x86_64
Build cmd: n/a (source-only verification)
Run cmd: n/a (source-only verification)

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: likely
Tested: 2026-07-23 04:51:43
Runtime: —
Kernel: 6.5-DEVELOPMENT #0 (combined-fix build, rc=0 -Werror, Thu Jul 23 04:36:20 UTC 2026)
fix.diff: findings/poc/DF-0380/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0380 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	689 B	↓ raw
fix.diff	suggested-fix	fix for race bug	385 B	view raw

VERDICT.md verdict source verification verdict

↓ download raw

DF-0380 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: race

Impact: dos

Source file: sys/netgraph/netgraph/ng_base.c

Mechanism

CONFIRMED: ng_unref decrements node->refs (plain int) under crit_enter only. Not MP-safe. Fix: use atomic_fetchadd_int.

Fix

See fix.diff for the git-apply-able patch.

Build validation

Combined kernel build with all 70 Low-severity fixes: rc=0, -Werror. All fixes compile cleanly in X86_64_GENERIC kernel configuration.

Guest: DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff compiles cleanly in combined kernel build (rc=0, -Werror). Source trace confirms bug at sys/netgraph/netgraph/ng_base.c:473.

Combined build: 70 fix.diffs applied to /usr/src, nativekernel KERNCONF=X86_64_GENERIC rc=0 -Werror. All fixes compile.

↓ fix.diff6.5-DEVELOPMENT #0 (combined-fix build, rc=0 -Werror, Thu Jul 23 04:36:20 UTC 2026)

Confirmed kernel references

Detail

Exploit chain

none (non-corruption Low severity finding; source-only confirmation)

Evidence (decisive lines)

Source-traced at sys/netgraph/netgraph/ng_base.c:473. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0380. No PoC binary (source-only verification).

Verified recommended fix

Use atomic_fetchadd_int for refcount decrement. Matches finding proposal.

Verdict

CONFIRMED source-only: ng_unref decrements refs under crit only. Not MP-safe.