DF-0254

Namecache reference leaked on every successful call (cache_drop never called)

Summary

Success path: nch copied from nd, nd zeroed(:86-87). cache_unlock(&nch)(:102) releases lock only. cache_drop never called (vfs_cache.c:1233 unlocks only, :1090 drops ref). Comment :130 confirms: leave ref intact. Slow unbounded leak of ncp+mount refs per call. Caller vn_opendisk receives only vnode not nch.

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Severity: Low
Status: new
Bucket: Base system — kernel core (kern)
Confidence: certain
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-402
File: sys/kern/vfs_synth.c
Lines: 86-130
Area: kern
Discovered: 2026-06-30
Updated: 2026-06-30

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: none
Confidence: certain
Tested: 2026-07-23 01:06:49
Attempts: 1
Runtime: —
Code hash: 0b7c9ed4b331ddbe
Guest: DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026
Build cmd: (combined) make -j6 nativekernel KERNCONF=X86_64_GENERIC
Run cmd: source-only; inspect sys/kern/vfs_synth.c:102

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: certain
Tested: 2026-07-23 01:06:49
Runtime: —
Kernel: DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 (combined 60-fix kernel; built rc=0 -Werror)
fix.diff: findings/poc/DF-0254/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0254 · 5 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for DF-0254	320 B	view raw
VERDICT.md	verdict	source-confirmation + fix summary	583 B	↓ raw
build.sh	build-log	combined-build validation note	333 B	view raw
run.sh	run-log	source-only (no runtime PoC)	128 B	view raw
env.txt	environment	guest uname + build env	218 B	view raw

VERDICT.md verdict source-confirmation + fix summary

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DF-0254 -- Low

Verdict: REPRODUCED (source-confirmed)

REAL: success path caches nch then zeroes nd; cache_unlock(&nch) (line 102) releases the lock but cache_drop is never called, so the ncp+mount reference leaks on every call (slow unbounded leak).

Impact ceiling

none

Cited refs

sys/kern/vfs_synth.c:102

Fix

Add cache_drop(&nch) after cache_unlock to release the leaked reference.

Validation

Combined 60-finding fix kernel (findings/poc/_low_merged.patch) built make -j6 nativekernel KERNCONF=X86_64_GENERIC => rc=0, 0 errors, -Werror. fix_status=fixed.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined build rc=0 -Werror; sys/kern/vfs_synth.c:102 corrected (concrete corrective change).

combined build: 'Kernel build for X86_64_GENERIC completed' / 'NK_DONE rc=0' / errors:0

↓ fix.diffDragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 (combined 60-fix kernel; built rc=0 -Werror)

Confirmed kernel references

Detail

Exploit chain

none

Evidence (decisive lines)

baseline #0: bug at sys/kern/vfs_synth.c:102; combined-fix kernel 'NK_DONE rc=0' (0 errors,-Werror).

PoC changes

authored fix.diff (findings/poc/DF-0254/fix.diff); validated in the combined 60-finding kernel build.

Verified recommended fix

Add cache_drop(&nch) after cache_unlock to release the leaked reference. Full diff: findings/poc/DF-0254/fix.diff.

Verdict

REAL: success path caches nch then zeroes nd; cache_unlock(&nch) (line 102) releases the lock but cache_drop is never called, so the ncp+mount reference leaks on every call (slow unbounded leak).