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DF-2331

Slave-controlled block-read byte count overflows sc->block_data[32] in interrupt handler

Summary

During SMBus block read interrupt handler trusts 8-bit count byte from ICH_D0 hardware register (ichsmb.c:575-576) to bound store loop into fixed-size sc->block_data[32] array (ichsmb_var.h:64). D0 holds slave-provided block length (0..255) not host pre-validated expected count. Slave returning count>32 drives loop at :580-597 to write up to 224 bytes past block_data corrupting adjacent struct lock mutex and following heap objects. ichsmb_bread validates caller-supplied count (1..32) and resets block_count=0 but interrupt handler reads block_count from D0 hardware with no bound check. Loop stores bytes at indices 32..254. Attacker: malicious SMBus slave (compromised EC/BMC hostile hotplug peripheral) or local /dev/smbusN block read to variable-length device. Impact: heap overflow up to 224 bytes kernel panic DoS or heap grooming to privilege escalation.

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PoC verification

Evidence pack

findings/poc/DF-2331 · 5 files
FileTypeDescriptionSize
VERDICT.md verdict analysis: code bug confirmed, gate confirmed, fix authored 1.4 KB ↓ raw
fix.diff suggested-fix git-apply-able defense-in-depth fix (verified --check clean) 577 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-2331 — PoC verdict

File: sys/bus/smbus/ichsmb/ichsmb.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)

The ichsmb block-read interrupt handler trusts the 8-bit count byte read from the ICH_D0 hardware register (slave-supplied, 0..255) to bound a store loop into the fixed-size sc->block_data[32] array. count>32 writes up to 224 bytes past block_data.

Cited lines

Why it does not reproduce on this guest

No Intel ICH SMBus controller / SMBus slave on the QEMU guest (PIIX3 0x7113 is reported as "none0", ichsmb does not attach; no /dev/smbus*).

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

Defense-in-depth fix

After reading block_count from ICH_D0, clamp it to nitems(sc->block_data) (32).

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-2331/fix.diff -> OK. No runtime test possible (HW/ACPI/device-gated).
↓ fix.diffper-fix-DF-2331

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-2331/{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-2331/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): ichsmb slave-controlled block-read byte count overflows block_data[32] (no ICH SMBus). 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.