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DF-2483

mpt_pci_attach returns success on every failure path causing NULL-deref / linked-list corruption on detach

Summary

The bad: error label of mpt_pci_attach unconditionally returns 0 (success) instead of error code. Newbus believes device DS_ALIVE and invokes mpt_pci_detach on kldunload/hot-unplug even when attach never completed. mpt_pci_detach calls mpt_detach which performs unconditional TAILQ_REMOVE. For disabled-device path (mpt_disable tunable) softc links.tqe_prev stays NULL so TAILQ_REMOVE writes to NULL panic. For inner-mpt_attach-failure path double TAILQ_REMOVE writes stale tqe_prev pointer into global mpt_tailq head silently corrupting list. Root/loader controlled trigger. kldunload mpt or PCIe hot-unplug after failed attach.

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PoC verification

Evidence pack

findings/poc/DF-2483 · 6 files
FileTypeDescriptionSize
VERDICT.md verdict Source trace confirming DF-2483 bug is real but HW-gated 1.2 KB ↓ raw
fix.diff suggested-fix Return ENXIO instead of 0 on the bad: error path 255 B view raw
env.txt environment Guest gate proof: kldstat, pciconf, camcontrol (no target HBA) 1.1 KB view raw
build.sh build-script No buildable PoC (HW-gated) 384 B view raw
run.sh run-script Gate verification commands 411 B view raw
README.md readme Overview of HW-gated finding 791 B ↓ raw
README.md readme Overview of HW-gated finding
↓ download raw

HW-gated SCSI/FC HBA driver finding

This finding targets a SCSI/FC/SATA HBA driver that is not present in this QEMU/KVM guest (only PIIX3 IDE + virtio). The driver cannot attach and the cited code path is unreachable at runtime.

Reproduction status: NOT REPRODUCED (HW-gated)

  • The source bug is confirmed real by line-by-line source trace (see VERDICT.md).
  • It cannot be triggered because the HBA hardware/driver does not exist on this guest.
  • A defense-in-depth fix.diff has been authored and validated with git apply --check.

Evidence

  • VERDICT.md — full source trace and analysis
  • env.txt — guest environment (kldstat, pciconf, camcontrol gate proof)
  • fix.diff — git-apply-able defense-in-depth fix
  • manifest.json — machine-readable catalog
VERDICT.md verdict Source trace confirming DF-2483 bug is real but HW-gated
↓ download raw

DF-2483 — mpt_pci_attach returns success on every failure path

Verdict: NOT REPRODUCED (HW-gated) — source bug CONFIRMED

Hardware gate

No LSI Logic MPT HBA in guest: kldstat shows only kernel/ehci/xhci; pciconf -l shows no LSI device. mpt PCI attach is never called.

Source trace (confirmed real bug)

File: sys/dev/disk/mpt/mpt_pci.c:597-609

The bad: error label unconditionally return (0) (success) at line 609:

bad:
    mpt_dma_mem_free(mpt);
    mpt_free_bus_resources(mpt);
    ...
    return (0);   // ← BUG: returns success despite failure

Newbus believes the device is DS_ALIVE and invokes mpt_pci_detach on kldunload/hot-unplug even when attach never completed. mpt_pci_detach calls mpt_detach which performs unconditional TAILQ_REMOVE. For the disabled-device path, softc->links.tqe_prev stays NULL, so TAILQ_REMOVE writes to NULL → panic. For the inner-attach-failure path, double TAILQ_REMOVE corrupts the global mpt_tailq head.

Fix

Changed return (0) to return (ENXIO) on the error path. See fix.diff.

Impact (on HW that has the HBA)

Low — panic or list corruption on kldunload/hot-unplug after failed attach.

Fix verification

not_testable
baseline no→ patch + rebuild →patched clean

not_testable: target driver cannot attach (no target HBA). fix.diff validated with git apply --check (EXIT=0); fix is correct by source trace.

git apply --check findings/poc/DF-2483/fix.diff => EXIT=0. No runtime test possible (no target HBA).
↓ fix.diffDragonFly 6.5-DEVELOPMENT #0 (unpatched with-src baseline — target driver not loadable on this guest)

Confirmed kernel references

Detail

Exploit chain

none — valid hard blocker (driver code path dead at runtime on this guest: no target HBA). No unprivileged->root path.

Evidence (decisive lines)

kldstat -> kernel/ehci/xhci only (no target driver); pciconf -l -> PIIX3 IDE + virtio only (no target HBA); camcontrol devlist -> only <QEMU QEMU DVD-ROM>. Source confirmed at cited lines.

PoC changes

Created findings/poc/DF-2483/{VERDICT.md,fix.diff,manifest.json,env.txt,build.sh,run.sh,README.md}. No PoC source (HW-gated).

Verified recommended fix

Defense-in-depth fix.diff closes the cited path (see findings/poc/DF-2483/fix.diff; git apply --check OK).

Verdict

NOT REPRODUCED (HW-gated). The bug is REAL in source (traced line-by-line): mpt_pci_attach returns 0 on every failure path (DS_ALIVE kept; TAILQ_REMOVE NULL-deref/double-remove on detach; needs LSI MPT). Gate confirmed: kldstat (only kernel+ehci+xhci; no isp/mpt/sili/trm/sbp module loaded), pciconf -l (no QLogic ISP/LSI MPT/SiliconImage/Tekram/FireWire HBA — only PIIX3 IDE atapci0 + virtio), camcontrol devlist (only QEMU DVD-ROM). The target driver cannot attach so the cited code path is dead at runtime on this guest.