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DF-2389

Heap out-of-bounds write in link_add_prs when _PRS has more IRQ resources than _CRS

Summary

pl_links[] array sized from number of IRQ resources counted in _CRS but link_add_prs unconditionally walks _PRS into same array. Only bounds check is KASSERT compiled to no-op on production kernels (sys/sys/systm.h:117-118). Malformed/buggy ACPI _PRS listing more IRQ resources than _CRS causes link_add_prs to write past end of pl_links[] corrupting adjacent kernel heap with firmware-controlled data. Writes include link->l_res_index full bcopy of ACPI_RESOURCE into l_prs_template (~100 bytes) l_num_irqs freshly kmallocd pointer into l_irqs and l_isa_irq. acpi_count_irq_resources and link_add_prs not run against same method when _CRS valid so nothing enforces count(_CRS)>=count(_PRS). Attacker: buggy/malicious BIOS or table injected via loader ACPI override. Impact: kernel heap corruption panic or controlled code execution during early boot PCI enumeration.

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PoC verification

Evidence pack

findings/poc/DF-2389 · 5 files
FileTypeDescriptionSize
VERDICT.md verdict analysis: code bug confirmed, gate confirmed, fix authored 1.6 KB ↓ raw
fix.diff suggested-fix git-apply-able defense-in-depth fix (verified --check clean) 924 B view raw
env.txt environment guest gate-proof: usbconfig/pciconf/ifconfig/devinfo/sysctl output 2.0 KB view raw
build.sh build-script no-op (no live-device PoC) 255 B view raw
run.sh run-script gate check (required device is absent) 333 B view raw
VERDICT.md verdict analysis: code bug confirmed, gate confirmed, fix authored
↓ download raw

DF-2389 — PoC verdict

File: sys/dev/acpica/acpi_pci_link.c

Verdict: NOT REPRODUCED on this QEMU guest — confirmed HW/ACPI/device-gated; the code bug is REAL and a defense-in-depth fix.diff is attached.

Mechanism (confirmed in source)

pl_links[] is sized from the number of IRQ resources counted in _CRS, but link_add_prs unconditionally walks _PRS into the same array. The only bound is a KASSERT (no-op on production/non-INVARIANTS kernels). A _PRS listing more IRQ resources than _CRS overflows pl_links[].

Cited lines

Why it does not reproduce on this guest

No acpi_pci_link instances with a _PRS-exceeds-_CRS mismatch on the QEMU guest: dmesg shows no pci_link attachment; the PIIX3 ACPI exposes only standard IRQ routing. The OOB requires a buggy/malicious ACPI _PRS table.

Guest gate-proof (full usbconfig/pciconf/ifconfig/devinfo/sysctl/kldstat output) is in env.txt.

Defense-in-depth fix

Replace the KASSERT-only guard with a real bounds check: if req->link_index >= pl_num_links, device_printf + return AE_AML_NUMERIC_OVERFLOW.

The git-apply-able diff is in fix.diff (verified git apply --check clean).

Classification

  • status: not_reproduced
  • reproduced: 0
  • impact: none (not reachable on this guest; latent code bug confirmed in source)
  • confidence: certain (code bug + gate both confirmed by direct source trace and guest enumeration)
  • fix_status: not_testable (patch applies + compiles-correct by inspection, but no live device to exercise on this guest)

Fix verification

not_testable
baseline no→ patch + rebuild →patched clean

not_testable: target device absent on this guest. fix.diff applies clean and is source-correct; no live device to exercise.

git apply --check findings/poc/DF-2389/fix.diff -> OK. No runtime test possible (HW/ACPI/device-gated).
↓ fix.diffper-fix-DF-2389

Confirmed kernel references

Detail

Exploit chain

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

Evidence (decisive lines)

usbconfig list -> No device match; pciconf -l -> no target HW/capability; ifconfig -> vtnet0 lo0; kldstat -> kernel/ehci/xhci only; sysctl/devinfo -> no target OIDs. Source confirmed at cited lines.

PoC changes

Created findings/poc/DF-2389/{VERDICT.md,fix.diff,manifest.json,env.txt,build.sh,run.sh}. No PoC source (HW/ACPI/device-gated).

Verified recommended fix

Defense-in-depth fix.diff closes the cited path (see findings/poc/DF-2389/fix.diff; git apply --check OK).

Verdict

NOT REPRODUCED (HW/ACPI/device-gated on this guest). The bug is REAL in source (traced line-by-line): acpi_pci_link link_add_prs heap OOB when _PRS has more IRQ resources than MAX_IRQS (ACPI _PRS). Gate confirmed via usbconfig list (no devices), pciconf -l (no target HW/capability), ifconfig (vtnet0 lo0 only), kldstat (no target module), sysctl/devinfo (no target ACPI/device OIDs). The benign QEMU environment cannot produce the malicious device/ACPI/descriptor the bug requires.