# VERDICT — DF-1492: r300_packet3_check missing per-opcode minimum COUNT

## Verdict

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

The bug is real and present in master DEV source at `sys/dev/drm/radeon/r300.c:1166-1248`,
but the affected driver attaches only to hardware not present in the audit QEMU
guest, so it cannot be live-triggered here. The fix.diff applies cleanly and
compiles with `-Werror` (kernel build rc=0; see fix_build.log).

## Mechanism (cited path → primitive → effect)

r300.c:1176 `idx = pkt->idx + 1;`. Several opcodes (PACKET3_INDX_BUFFER :1191, _3D_DRAW_IMMD :1202, _3D_DRAW_VBUF :1229, _3D_DRAW_INDX :1243) read `ib[idx+1]` without checking pkt->count. The parser radeon_cs.c:768 accepts a packet when `(pkt->count+1+pkt->idx) < length_dw`, so a COUNT=0 packet at end of IB has idx+1 == length_dw → ib[idx+1] reads past the IB allocation.

## Reachability on this guest

No — radeon DRM HW-gated. Trigger is a CS IB ending with a packet3 (INDX_BUFFER/DRAW_*) of COUNT=0.

## Phase 6 — escalation potential

This is a IB OOB 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).

For findings in this batch that *are* corruption-class on hardware they would
be live-tested on (NIC cards, RAID HBAs, AMD/Intel GPUs), the realistic
escalation ceiling is documented per finding (info-leak vs DoS vs latent
privesc). No `uid=0` claim is made — none is reachable on this guest.

## 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 `make -j6 nativekernel
  KERNCONF=X86_64_GENERIC` (kernel build rc=0; affected module builds
  radeon.ko/amdgpu.ko/sound.ko/i915.ko/vga_switcheroo.ko all produced).
- For musycc.c (not in any default config) the file was compiled standalone
  with the kernel `-Werror` cflags — rc=0.

Reject packets with `pkt->count < 1` at the top of r300_packet3_check (after the idx assignment).

## 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.