# VERDICT — DF-1516: intel_overlay.c u32 integer overflow in offset bounds check

## Verdict

**INCONCLUSIVE (HW/module gated) — source-level confirmed, fix validated.**

The bug is real and present in master DEV source at `sys/dev/drm/i915/intel_overlay.c:1033-1051`, but
the affected driver attaches only to hardware not present in the audit QEMU
guest (only virtio+PIIX3 PCI devices, no AMD/Intel GPUs, no ath NICs, no
AdvanSys SCSI, no mfi/tws/mrsas RAID, etc.), so it cannot be live-triggered
here. The `fix.diff` applies cleanly and the patched kernel compiles with
`-Werror` (combined build rc=0; see `fix_apply.log`).

## Mechanism (cited path → primitive → effect)

check_overlay_src computes tmp = rec->stride_Y * rec->src_height (both u32) then rec->offset_Y + tmp > new_bo->base.size. Both additions are u32 and silently wrap mod 2^32; the wrapped value compared as u64 against size_t passes the check. The packed (line 1033), planar Y (1044-1045) and planar UV (1049-1050) sites all have the same flaw.

## Reachability on this guest

No — `sys/dev/drm/i915/intel_overlay.c:1033-1051` is in a driver/module that only attaches
to hardware absent from the audit guest. The trigger requires the relevant
PCI device (or, for VBIOS-driven GPU paths, the actual GPU + a crafted VBIOS
loaded by root or via VFIO passthrough).

## Phase 6 — escalation potential

This is a Integer overflow -> bounds check bypass -> OOB GPU read primitive. On real hardware
it could be triggered by an unprivileged user (via crafted packets for the
NIC findings, via DRM ioctls for the GPU findings, via CAM/pass for the SCSI
findings). On **this guest** there is no live primitive to convert. Per
Phase 6 rules this is the "dead/unreachable at runtime on this guest" hard
blocker; the primitive is proven at the source/harness level (the cited
path:line is real and unfixed in master).

Realistic impact ceiling on suitable HW: **GPU memory OOB read / cross-buffer leak via crafted DRM overlay params**.

## Phase 8 — fix validation

`fix.diff` is a minimal, targeted fix at the root cause confirmed above.

- **Applied cleanly** with `patch -p1 --forward` (verified in `fix_apply.log`).
- **Compiled with `-Werror`** as part of the combined
  `make -j6 nativekernel KERNCONF=X86_64_GENERIC` build (kernel build rc=0;
  see `manifest.json`).
- For HW-gated findings the patched code path is not exercisable on this
  guest, so the fix is validated at the apply + compile level only.

Fix approach: Compute stride*height and offset+tmp as uint64_t in all three sites.

## PoC changes

Source-level confirmation only; no userspace harness written because the bug
cannot be exercised on this guest without the relevant HW. The placeholder
`build.sh`/`run.sh` echo pointers to `VERDICT.md` and the module/kernel
rebuild path.