# DF-0177 — cttykqfilter forwards knote to ttyvp with no token and no reference

**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. cttykqfilter reads ttyvp via cttyvp(p) macro(:284) with no token, then immediately VOP_KQFILTER(ttyvp,kn)(:287) with no vget/vref. Same lifetime window as DF-0176 — can register a knote on a revoked tty or deref a reclaimed vnode.

## Kernel references (confirmed)
- `sys/kern/tty_tty.c:74`
- `sys/kern/tty_tty.c:284`
- `sys/kern/tty_tty.c:287`

## Fix

Hold a vnode reference (vhold/vdrop) across VOP_KQFILTER. 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-0177/../../_combined_build.log` (reference; full log at audit time).
- Combined kernel.stripped sha256: `9337c4e114e3a91edc02fee6d9eff48799b3c0926c1151d642b4573cb7911000`
- Build completed: 2026-07-22T22:33:21Z