{
 "finding_id": "DF-2981",
 "status": "not_reproduced",
 "reproduced": 0,
 "impact": "none",
 "confidence": "certain",
 "verdict": "Line-accurate confirmation, fix compile-validated; runtime demonstration deliberately not attempted - the failing-load branch is provably unreachable with the current x86_64 MD allocator (tag is created with nsegments=1 and maxsegsz==maxsize so a legal buffer cannot split; subr_busdma.c:64-67). The defect is certain from source: the glue callback _bus_dmamem_coherent_cb returns early on error without recording it (subr_busdma.c:46-47), while the MD bus_dmamap_load always returns 0 for synchronous loads, delivering the error only through the callback (busdma_machdep.c: callback(...error); return 0). bus_dmamem_coherent therefore returns 0 (success) with dmem_busaddr==0 and a never-loaded map if a load ever fails - the caller programs its device to DMA at physical address 0. Fix (carg.error propagation) compiled in the combined F40FIX kernel build.",
 "exploit_chain": "",
 "evidence": "VERDICT.md with path:line citations; run.log where a live demo exists; fix.diff",
 "kernel_refs": [
  "sys/kern/subr_busdma.c:46",
  "sys/kern/subr_busdma.c:79",
  "sys/kern/subr_busdma.c:94",
  "sys/platform/pc64/x86_64/busdma_machdep.c:804"
 ],
 "poc_changes": "n/a - no PoC (unreachable branch); verification by source trace + compile validation",
 "attempts": 0,
 "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": 30,
 "guest_dirty": 0,
 "build_cmd": "see build.sh",
 "run_cmd": "see run.sh",
 "code_hash": null,
 "notes": "",
 "recommended_fix": "propagate the synchronous callback error through a carg struct; bus_dmamem_coherent fails and frees on carg.error",
 "fix_status": "compile_validated",
 "fix_verdict": "fix.diff applied in the F40FIX verification kernel build (RC=0, zero -Werror errors); no runtime A/B for this item (line-certain hardening)"
}