PoC verification

Evidence pack

findings/poc/DF-0125 · 5 files

File	Type	Description	Size
VERDICT.md	verdict	source-trace confirmation + fix rationale	1.8 KB	↓ raw
fix.diff	suggested-fix	git-apply-able fix for DF-0125	791 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

VERDICT.md verdict source-trace confirmation + fix rationale

↓ download raw

DF-0125 — sysctl_kern_consmute races cnread/cnwrite/cnioctl forwarding

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. sysctl_kern_consmute (RW sysctl) calls cninit_finish/cnuninit which mutate cn_fwd_ops/cn_dev with no serialization. cnread(:449)/cnwrite(:461)/cnioctl(:479) check cn_fwd_ops!=NULL then dispatch via dev_doperate — classic check-then-use TOCTOU. Root-only trigger (sysctl write). Low severity: requires root to flip consmute during an active console read/write window.

Kernel references (confirmed)

Fix

Add a lwkt_token cn_conslock acquired in sysctl_kern_consmute around the mutation block (writer-side serialization). 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-0125/../../_combined_build.log (reference; full log at audit time).
Combined kernel.stripped sha256: 9337c4e114e3a91edc02fee6d9eff48799b3c0926c1151d642b4573cb7911000
Build completed: 2026-07-22T22:33:21Z

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined build: all 50 fix.diffs applied to /usr/src and built in a single make -j6 nativekernel KERNCONF=X86_64_GENERIC -> rc=0, 0 errors, 0 warnings under -Werror. This fix compiles clean.

combined build: NK_DONE rc=0; errors:0; warnings(excl missing-include-dirs):0; kernel.stripped sha256:9337c4e114e3a91edc02fee6d9eff48799b3c0926c1151d642b4573cb7911000

↓ fix.diffDragonFly 6.5-DEVELOPMENT (50-diff combined single-fix kernel; nativekernel rc=0, kernel.stripped sha256 9337c4e114e3a91edc02fee6d9eff48799b3c0926c1151d642b4573cb7911000)

Confirmed kernel references

Detail

Exploit chain

none — Low-severity source-only confirmation (no memory-corruption primitive; no escalation chain applicable).

Evidence (decisive lines)

Source-trace confirmed at sys/kern/tty_cons.c:257, sys/kern/tty_cons.c:449, sys/kern/tty_cons.c:479. fix.diff applied + compiled clean as part of 50-diff combined nativekernel build (rc=0, 0 errors, 0 warnings under -Werror). Combined kernel.stripped sha256=9337c4e114e3a91edc02fee6d9eff48799b3c0926c1151d642b4573cb7911000. Full build log (35649 lines) in findings/poc/_combined_build.log.

PoC changes

Authored fix.diff (git-apply-able) in findings/poc/DF-0125/. Wrote VERDICT.md, manifest.json, build.sh, run.sh, env.txt. No runtime PoC (source-only Low finding).

Verified recommended fix

Add lwkt_token cn_conslock in sysctl_kern_consmute around the mutation block; supersedes finding proposal. Full diff in findings/poc/DF-0125/fix.diff.

Verdict

CONFIRMED. sysctl_kern_consmute mutates cn_fwd_ops/cn_dev (cninit_finish/cnuninit) with no lock; cnread/cnwrite/cnioctl check-then-dispatch cn_fwd_ops TOCTOU. Root-only sysctl trigger.

sysctl_kern_consmute races cnread/cnwrite/cnioctl forwarding (no lock)

Summary

Discussion (0)