Summary

cttyvp(p) macro(:74-75) derefs p_session->s_ttyvp. Writers use proc_token(tty.c:334). Readers hold at most p_token(ioctl only) or nothing(open,read,write,kqfilter). p_token!=proc_token so no serialization. Pointer reads atomic, vnode pooled not freed -> stale-but-valid vnode not wild pointer. Root cause of DF-0176/0177.

PoC verification

Evidence pack

findings/poc/DF-0178 · 5 files

File	Type	Description	Size
VERDICT.md	verdict	source-trace confirmation + fix rationale	1.5 KB	↓ raw
fix.diff	suggested-fix	git-apply-able fix for DF-0178	579 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-0178 — cttyvp() snapshot read of s_ttyvp unsynchronized

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. cttyvp(p) macro derefs p_session->s_ttyvp. Writers use proc_token(tty.c:334). Readers hold at most p_token or nothing. p_token!=proc_token so no serialization. Pointer reads are atomic; vnode pooled not freed → stale-but-valid, not wild pointer. Root cause of DF-0176/0177.

Kernel references (confirmed)

Fix

Document the unsynchronized snapshot contract in the cttyvp macro comment. Matches 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-0178/../../_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 (rc=0).

NK_DONE rc=0; errors:0

↓ fix.diffDragonFly 6.5-DEVELOPMENT (50-diff combined; nativekernel rc=0)

Confirmed kernel references

Detail

Exploit chain

none — Low-severity source-only confirmation.

Evidence (decisive lines)

Source-trace confirmed at sys/kern/tty_tty.c:74, sys/kern/tty_tty.c:75. Combined build rc=0.

PoC changes

Authored fix.diff in findings/poc/DF-0178/.

Verified recommended fix

Document the unsynchronized snapshot contract; matches finding proposal.

Verdict

CONFIRMED. cttyvp macro derefs s_ttyvp unsynchronized vs proc_token writers. Stale-but-valid vnode (pooled). Root cause of DF-0176/0177.

cttyvp() snapshot read of s_ttyvp unsynchronized vs proc_token-held writers