DF-2987 / verdict.json
{ "finding_id": "DF-2987", "status": "reproduced", "reproduced": 1, "impact": "none", "confidence": "certain", "verdict": "Reproduced mechanically with a KMOD probe on the stock INVARIANTS guest: refcount_release() on a zero count silently wrapped 0 -> 0xFFFFFFFF and returned FALSE - no assert, no diagnostic (ref2987 KMOD log; the blind atomic_fetchadd_int is at refcount.h:54-70). A wrapped counter also wedges refcount_wait callers into the 60s-polled slowpath (kern_refcount.c:65-76). Defense-in-depth (kernel-internal primitive). Fix mirrors the DF-2941 sysref floor: INVARIANTS-only KASSERTs on the put side; compiled in the F40FIX build. The fixed-kernel A/B (assert trip) was intentionally NOT executed - it would panic the shared verification kernel mid-batch.", "exploit_chain": "", "evidence": "VERDICT.md with path:line citations; run.log where a live demo exists; fix.diff", "kernel_refs": [ "sys/sys/refcount.h:54", "sys/sys/refcount.h:70", "sys/kern/kern_refcount.c:65" ], "poc_changes": "n/a", "attempts": 1, "guest_uname": "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", "runtime_sec": 20, "guest_dirty": 0, "build_cmd": "see build.sh", "run_cmd": "see run.sh", "code_hash": "5ce515a9951183f468c5f0210e0c14be9111ce759815a7272ced3e4138bfc275", "notes": "", "recommended_fix": "INVARIANTS-only put-side floor asserts (release: old!=0; release_n: old>=i)", "fix_status": "compile_validated", "fix_verdict": "compiled in the F40FIX INVARIANTS build. Runtime trip intentionally not executed (assert would panic the shared kernel mid-batch); the stock-side silent 0->0xFFFFFFFF wrap is demonstrated live." } |