# VERDICT — DF-1490: epic_rx_done 16-bit rxlength has no upper-bound check

## Verdict

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

The bug is real and present in master DEV source at `sys/dev/netif/tx/if_tx.c:582, 600`,
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 582 `len = desc->rxlength - ETHER_CRC_LEN;` where desc->rxlength is volatile u_int16_t (0..65535). For rxlength<4, the int subtraction wraps to 65532..65534 (then truncates to u_int16_t back to 65532..65534). Line 600 `m->m_pkthdr.len = m->m_len = len;` assigns to the cluster mbuf with NO bound check vs MCLBYTES=2048. if_input then reads m->m_len bytes from a 2048-byte cluster → OOB heap read.

## Reachability on this guest

No — tx(4) (SMC EPIC/83c170) is in GENERIC but only attaches to SMC EtherPower II PCI NICs. Not present in audit guest.

## Phase 6 — escalation potential

This is a heap OOB read (DMA-derived) 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 (len > MCLBYTES) { IFNET_STAT_INC(ierrors); desc->status=0x8000; continue; }` between the rxlength computation and the mbuf 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.