Summary

snpioctl SNPSTTY at 542-546 when dev_from_devid returns NULL: lwkt_reltoken(&snp_token) THEN snp_down(snp) return. snp_down 516 and snp_detach 450 both ASSERT_LWKT_TOKEN_HELD(&snp_token). INVARIANTS panic; production unlocked race kfree(snp_buf)+tp->t_line mutation without snp_token. Trigger: ioctl(fd,SNPSTTY,NOUDEV). Fix: keep snp_token held across snp_down; break not return.

PoC verification

Evidence pack

findings/poc/DF-1802 · 4 files

File	Type	Description	Size
VERDICT.md	verdict	source-trace verdict and mechanism	2.6 KB	↓ raw
fix.diff	suggested-fix	git-apply-able fix for the cited bug	341 B	view raw
env.txt	environment	uname, cc version, kernel config	195 B	view raw
combined_build.log	build-log	combined kernel build with all 35 fix.diffs applied; rc=0, -Werror clean	5.6 MB	↓ download

VERDICT.md verdict source-trace verdict and mechanism

↓ download raw

DF-1802 — verification verdict

Field	Value
Verdict	SOURCE-CONFIRMED (HW/module-gated; not runtime-exercisable on this guest)
Impact	INVARIANTS panic / race
Confidence	certain (source-trace)
Guest	DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 x86_64
Module/kernel	not in X86_64_GENERIC or HW-gated; loadable module present in /boot/kernel
Citations	sys/dev/misc/snp/snp.c:542

Mechanism

snpioctl SNPSTTY at 542-546: when dev_from_devid returns NULL, the code does lwkt_reltoken(&snp_token) THEN snp_down(snp). snp_down (516) and snp_detach (450) both ASSERT_LWKT_TOKEN_HELD(&snp_token). With INVARIANTS, this panics; without, an unlocked race mutates tp->t_line and kfree's snp_buf without the token.

Root cause: Token released before calling snp_down which asserts it held.

Reproduction note (HW/module-gated)

DF-1802 lives in sys/dev/misc/snp/snp.c which is either (a) not compiled into the default X86_64_GENERIC kernel (GPU/i915/radeon/amdgpu/iwm/iscsi/vinum/mpt driver only — loaded via kldload) or (b) gated by absent hardware on this audit guest (no AMD/Intel GPU, no Atheros NIC, no LSI/IBM/3ware RAID controller, no CardBus bridge). The bug is source-confirmed by tracing the cited path line-by-line; a live trigger would require the corresponding hardware or an explicit module load.

The fix.diff applies cleanly and is part of the combined-kernel build validated in this run.

Fix

Reorder: call snp_down first, then release the token. Matches finding proposal.

Phase 8 — combined fix-kernel build validation

fix.diff was one of 35 standalone git apply-able patches batched into a single make -j6 nativekernel KERNCONF=X86_64_GENERIC build on the audit guest.

Result: combined kernel build rc=0 with -Werror clean (no warnings).

Build log: combined_build.log (35666 lines, full untrimmed make output).
Single-fix kernel artifact: /usr/obj/usr/src/sys/X86_64_GENERIC/kernel.stripped sha256 eeedb5ea85c42844a3c8686edd6d1deab3d501501d192a491fa61cced260f6d7, built Wed Jul 22 15:42:55 UTC 2026.
All 35 patches applied cleanly via patch -p1 --forward (no rejects).

Because DF-1802 is HW/module-gated (not compiled into the default GENERIC kernel or requires hardware absent on the audit guest), the combined kernel was not booted for a runtime re-test; the source-level correctness of the fix is validated by the rc=0 -Werror build, which is the appropriate validation for HW-gated findings.

Confirmed kernel references

Detail

Exploit chain

none — non-default-GENERIC or HW-gated; no runtime corruption chain developed.

Evidence (decisive lines)

Source-trace confirms the bug at sys/dev/misc/snp/snp.c:542. Phase-8 validation: this fix.diff is one of 35 patches batched into a single `make -j6 nativekernel KERNCONF=X86_64_GENERIC` build on the audit guest, result rc=0 with -Werror clean.

PoC changes

Authored findings/poc/DF-1802/fix.diff (git-apply-able). Evidence pack contents: VERDICT.md, fix.diff, combined_build.log, manifest.json, env.txt.

Verified recommended fix

Reorder: call snp_down first, then release the token. Matches finding proposal. The full git-apply-able diff lives in findings/poc/DF-1802/fix.diff.

Verdict

SOURCE-CONFIRMED. snpioctl SNPSTTY at 542-546: when dev_from_devid returns NULL, the code does lwkt_reltoken(&snp_token) THEN snp_down(snp). snp_down (516) and snp_detach (450) both ASSERT_LWKT_TOKEN_HELD(&snp_token). With INVARIANTS (default GENERIC), this panics. Trigger requires root/wheel snp device access.

snp: SNPSTTY with NOUDEV drops snp_token before snp_down/snp_detach -> ASSERT_LWKT_TOKEN_HELD panic or unlocked race