# DF-1821 Verification

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

The cited defect exists in the audited source at `sys/dev/raid/vinum/vinumraid5.c:142-201`. 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)
vinum (loaded as module, not in GENERIC; also root-only). Source: bre5 uses (plex->subdisks-1) as divisor at L153/184/201; for a degenerate <2-subdisk plex this divides by zero. Normally the diskaddr>=plex->length guard at L142 prevents reaching these because plex->length=0 for such plexes, but the divide-by-zero is still latent if the invariant is broken.

## Recommended fix
Guard at function entry: if (plex->subdisks < 2) return REQUEST_EOF before any division.

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.