# DF-1849 Verification

## Verdict
**SOURCE-CONFIRMED, INCONCLUSIVE-RUNTIME (HW/module gated).**

The cited defect exists in the audited source at `sys/dev/netif/fwe/if_fwe.c:560-569`. Reproduction
on the running guest is **not possible** because the affected code path is
gated behind hardware that is not present in the audit QEMU/KVM guest
(no AMD/i915 GPU, no LSI MegaRAID, no MMC/SDHCI controller, no FireWire, no
ATAPI floppy, etc.) and/or lives in a kernel module that is not loaded on the
GENERIC-running guest.

## Mechanism (source-only confirmation)
fwe (Ethernet over FireWire) IS in GENERIC but no FireWire HW in guest. Source: fwe_as_input at L546 extracts fp=mtod(...). stream.len is a u16 bitfield populated directly by the OHCI controller from the on-wire isochronous packet header (attacker-controlled). The check at L560 only rejects <ETHER_ALIGN+sizeof(ether_header); large stream.len drives m->m_len past m_ext.ext_size.

## Recommended fix
Cap fp->mode.stream.len against m->m_ext.ext_size before computing m->m_len.

The full `git apply`-able diff lives in `fix.diff` in this folder; it was
applied as part of a single combined 41-finding kernel build that compiled
cleanly (rc=0, -Werror clean) — see `../fix_build_summary.txt`.

## Build validation
* `git apply --check` on this fix.diff: **OK**
* Combined kernel build (`X86_64_GENERIC`, INVARIANTS ON) with all 41
  findings' fix.diffs applied: **rc=0**, no warnings, no errors.
* The patched kernel was not booted/run because the affected code path
  requires hardware that the audit guest does not have.