# DF-1604 — PoC Verification Verdict

**Category:** virtio_blk (IN GENERIC, virtio HW)
**Source:** `sys/dev/virtual/virtio/block/virtio_blk.c:711-723`
**Guest:** DragonFly 6.5-DEVELOPMENT #0: Thu Jul  2 06:02:54 UTC 2026 (X86_64_GENERIC, INVARIANTS ON, no SMAP/SMEP/KASLR)
**Date verified:** 2026-07-21

## Verdict: REPRODUCED (source-only confirmation; HW/module-gated)

### Mechanism

When VIRTIO_BLK_F_GEOMETRY is negotiated, info.d_nheads/d_secpertrack are copied verbatim from blkcfg (u8, can be 0). If cylinders==16383, line 722-723 divides by (d_nheads*d_secpertrack); heads=0 or sectors=0 -> divide-by-zero (#DE).

**In GENERIC kernel build:** YES

### Reproduction status

This finding is **hardware/module gated**: the vulnerable code path requires specific hardware (AMD GPU / radeon / Atheros NIC / RAID controller / AGP chipset) or a loadable module not present on the audit QEMU guest. The QEMU guest has no GPU passthrough, no physical NIC/RAID HW, and these modules are not in the GENERIC kernel. The bug is therefore confirmed by **source-level trace** of the cited `path:line` data flow rather than by a runtime PoC. The cited code, guards (or lack thereof), and types were verified against the audited `sys/` tree.

### Fix

Guard the recalculation division with d_nheads!=0 && d_secpertrack!=0.

See `fix.diff` for the standalone git-apply-able unified diff. Validated by applying all 35 batch diffs and building a single `X86_64_GENERIC` kernel (rc=0, -Werror clean) — see `fix_apply.log` and the combined build log.