# DF-2510 — Unbounded ctlr->channels (up to 32 from AHCI CAP/PI MMIO) overflows interrupt[8]

## Verdict
NOT REPRODUCED (hardware / trigger gated). The cited vulnerable code path exists
in `sys/dev/disk/nata/chipsets/ata-ahci.c` and is compiled into the X86_64_GENERIC kernel, but it is **not
exercisable at runtime on this QEMU guest** because the required HBA / device /
trigger is absent. Confidence in the source bug itself: **certain**.

## Why it cannot be reproduced here (the gate)
Hard-gated: needs an AHCI controller. The guest has NO AHCI (PIIX3 IDE only); ata_ahci_chipinit never runs.

See `env.txt` for the full guest PCI/kldstat/dev-node inventory that proves the
gate.

## The bug is real in source (traced line-by-line)
Cited path:
- sys/dev/disk/nata/chipsets/ata-ahci.c:100-103
- sys/dev/disk/nata/ata-pci.h:67
- The vulnerable construct is present verbatim in the current master source
  (confirmed by direct read of the cited lines during verification).
- A defense-in-depth `fix.diff` that closes the path is included and was
  validated to apply (`git apply --check`) **and** to compile cleanly in a full
  X86_64_GENERIC kernel build with `-Werror` (build rc=0).

## Fix
Cap ctlr->channels to NELEM(ctlr->interrupt) (8) after deriving it from CAP/PI, complementing the DF-2492 bounds checks in the interrupt dispatch.

The standalone git-apply-able diff is `fix.diff`.

## Reproduce
`./build.sh && ./run.sh` — both are no-ops on this guest by design (the gate
holds). Exercising the path requires the corresponding HBA/device/trigger
(ATA disk / ATAPI floppy or tape / NVMe controller / AdvanSys HBA / AHCI
controller / a malicious ATAPI device / a CD burner / hot-unplug).

## Status
status: not_reproduced  | reproduced: 0 | impact: none (HW-gated)
fix_status: not_testable (path cannot run on this guest; diff applies + compiles)