# VERDICT — DF-1478: my_rxeof FLNG has no upper-bound check vs MCLBYTES

## Verdict

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

The bug is real and present in master DEV source at `sys/dev/netif/my/if_my.c:1105-1131`,
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)

Line 1105 `total_len = (rxstat & MY_FLNGMASK) >> MY_FLNGShift;` — FLNG is 12-bit (0..4095). Line 1106 subtracts ETHER_CRC_LEN. RX cluster is MCLBYTES=2048 (programmed as RBS=MCLBYTES-1 at 1076). For FLNG in [2053,4095], total_len 2049..4091 exceeds 2048. Line 1110 m_devget(..., total_len, ...) and line 1131 `m->m_len = total_len` both operate on a length > the cluster size → OOB heap read of up to ~2KB past the cluster.

## Reachability on this guest

No — my(4) is in LINT64 only (not in GENERIC). Myson MTd80x/MTD89x PCI NIC needed; not present in audit guest.

## Phase 6 — escalation potential

This is a heap OOB read (DMA-derived length) 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.

Add `if (total_len > MCLBYTES) { drop; continue; }` between the FLNG extraction and the m_devget/newbuf path.

## 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.