Summary

snpread 265 snpkqfilter 636 snpfilter_rd 678 all do tp=snp->snp_tty; lwkt_gettoken(&tp->t_token) BEFORE checking snp_tty==NULL. snpopen 434 inits snp_tty NULL. read() or kqueue on open-but-unattached fd panics. snpwrite 217 does correct NULL-check-first. /dev/snpN 0600 root:wheel. Fix: if(tp==NULL) return before gettoken.

PoC verification

Evidence pack

findings/poc/DF-1801 · 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	716 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-1801 — verification verdict

Field	Value
Verdict	SOURCE-CONFIRMED (HW/module-gated; not runtime-exercisable on this guest)
Impact	panic (NULL deref)
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:265, sys/dev/misc/snp/snp.c:636, sys/dev/misc/snp/snp.c:678

Mechanism

snpread (265), snpkqfilter (636), snpfilter_rd (678) all do tp=snp->snp_tty; lwkt_gettoken(&tp->t_token) BEFORE checking snp_tty==NULL. snpopen inits snp_tty to NULL; an open-but-unattached fd therefore dereferences NULL tp -> panic. snpwrite at 217 does the correct NULL-check-first.

Root cause: NULL check ordered after the dereference.

Reproduction note (HW/module-gated)

DF-1801 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

Move the NULL check before lwkt_gettoken in all three sites. 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-1801 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:265. 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-1801/fix.diff (git-apply-able). Evidence pack contents: VERDICT.md, fix.diff, combined_build.log, manifest.json, env.txt.

Verified recommended fix

Move the NULL check before lwkt_gettoken in all three sites. Matches finding proposal. The full git-apply-able diff lives in findings/poc/DF-1801/fix.diff.

Verdict

SOURCE-CONFIRMED. snpread (265), snpkqfilter (636), snpfilter_rd (678) all do tp=snp->snp_tty; lwkt_gettoken(&tp->t_token) BEFORE checking snp_tty==NULL. snpopen inits snp_tty=NULL; an open-but-unattached fd dereferences NULL tp -> panic. snpwrite at 217 does the correct NULL-check-first. snp is a loadable pseudo-device (mode 0600 root:wheel) — trigger requires opening /dev/snpN which needs root/wheel.

snp: NULL-deref panic when read/kqfilter issued on unattached /dev/snpN device