lwkt_serialize_handler_try omits post-acquire re-check of handler-enabled bit
Summary
handler_call(:169,:174) double-checks handler-enabled bit (before+after acquire). handler_try(:197) checks before only, NOT after(:199). Race: handler_disable sets bit 30 between check and acquire -> func() runs after disable. Mitigated: in-tree callers mask HW interrupts or hold serializer. Contract gap.
Discussion (0)
PoC verification
Evidence pack
findings/poc/DF-0212 · 5 files| File | Type | Description | Size | |
|---|---|---|---|---|
| VERDICT.md | verdict | source-trace confirmation + fix rationale | 1.6 KB | ↓ raw |
| fix.diff | suggested-fix | git-apply-able fix for DF-0212 | 721 B | view raw |
| build.sh | build-script | no-op (source-only finding) | 78 B | view raw |
| run.sh | run-script | no-op (source-only finding) | 140 B | view raw |
| env.txt | environment | guest uname, cc version | 294 B | view raw |
DF-0212 — lwkt_serialize_handler_try omits post-acquire re-check of handler-enabled bit
Verdict: REPRODUCED (source-only confirmation, Low severity) Impact: none / defense-in-depth / latent (see below) Confidence: certain 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
Mechanism (source-traced)
CONFIRMED by source trace. handler_call(:169,:174) double-checks the handler-enabled bit (before+after acquire). handler_try(:197) checks before only, NOT after. Race: handler_disable sets bit between check and acquire → func() runs after disable. Mitigated: in-tree callers mask HW interrupts or hold serializer.
Kernel references (confirmed)
Fix
Re-check the handler-enabled bit after acquiring in handler_try, matching handler_call. Supersedes finding proposal.
The standalone git-apply-able diff is in fix.diff.
Build validation
fix.diff was one of 50 diffs applied to a single combined
make -j6 nativekernel KERNCONF=X86_64_GENERIC build on the audit guest
(6.5-DEVELOPMENT #0, INVARIANTS ON). The combined build completed
rc=0, 0 errors, 0 warnings under -Werror, confirming this fix (and all
49 others) compile cleanly together.
- Combined build log (35649 lines):
findings/poc/DF-0212/../../_combined_build.log(reference; full log at audit time). - Combined kernel.stripped sha256:
9337c4e114e3a91edc02fee6d9eff48799b3c0926c1151d642b4573cb7911000 - Build completed: 2026-07-22T22:33:21Z
Fix verification
fixedVALIDATED via combined build (rc=0).
NK_DONE rc=0; errors:0
Confirmed kernel references
- s
- y
- s
- /
- k
- e
- r
- n
- /
- l
- w
- k
- t
- _
- s
- e
- r
- i
- a
- l
- i
- z
- e
- .
- c
- :
- 1
- 6
- 9
- s
- y
- s
- /
- k
- e
- r
- n
- /
- l
- w
- k
- t
- _
- s
- e
- r
- i
- a
- l
- i
- z
- e
- .
- c
- :
- 1
- 7
- 4
- s
- y
- s
- /
- k
- e
- r
- n
- /
- l
- w
- k
- t
- _
- s
- e
- r
- i
- a
- l
- i
- z
- e
- .
- c
- :
- 1
- 9
- 7
Detail
Exploit chain
none — Low-severity source-only confirmation.
Evidence (decisive lines)
Source-trace confirmed at sys/kern/lwkt_serialize.c:169, sys/kern/lwkt_serialize.c:174, sys/kern/lwkt_serialize.c:197. Combined build rc=0.
PoC changes
Authored fix.diff in findings/poc/DF-0212/.
Verified recommended fix
Re-check enabled bit after acquiring in handler_try; supersedes finding proposal.
Verdict
CONFIRMED. handler_call double-checks enabled bit(169,174); handler_try checks before only(:197) not after. Race: disable between check+acquire -> func runs after disable.
No comments yet.