DF-2349

uint8_t loop index in uvc_ctrl_init_dev wraps causing infinite loop and heap OOB write on malicious UVC descriptor

Summary

uvc_ctrl_init_dev() iterates per-unit bmControls bitmap with uint8_t loop index i bounded by bCtrlSize*8. bCtrlSize taken verbatim from untrusted UVC Camera-Terminal/Processing-Unit/Extension-Unit descriptor (no upstream clamp can be up to ~240 bytes). Any bCtrlSize>=32 makes bound>=256 so i wraps 255->0 and loop never terminates. On each wrap re-processes set bits and marches ctrl (struct uvc_control*) far past end of allocated topo_node->controls array writing topo_node/index/uvc_data/info fields into adjacent kernel heap. uvc_ctrl_initialize_control performs heap writes through ctrl (kmalloc into ctrl->uvc_data full struct copy into ctrl->info). Allocation sized to exactly nctrls entries computed correctly by uvc_ctrl_count_control (uses int i). After first 256 iterations consume all nctrls slots every subsequent set-bit iteration writes past topo_node->controls+nctrls. Descriptor value fully attacker-controlled. Attacker: malicious USB webcam. Impact: kernel memory corruption local privilege escalation via slab grooming or reliable panic DoS.

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Severity: High
Status: new
Bucket: Kernel memory corruption (UAF / OOB write)
Confidence: certain
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CWE: CWE-787 Out-of-bounds Write
File: sys/bus/u4b/uvc/uvc_ctrls.c
Lines: 925-973
Area: hw
Discovered: 2026-07-28
Updated: 2026-07-28

Team triage

untriaged

priority: — · owner: —

PoC verification

not_reproduced

Status: not_reproduced
Reproduced: no
Impact: none
Confidence: certain
Tested: 2026-08-09 14:46:05
Attempts: 1
Runtime: 1s
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64
Build cmd: n/a (HW/ACPI/device-gated)
Run cmd: ./run.sh # gate check; target device absent

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Fix verification

not_testable

Fix status: not_testable
Baseline reproduced: no
Patched reproduced: no
Confidence: certain
Tested: 2026-08-09 14:46:05
Runtime: —
Kernel: per-fix-DF-2349
fix.diff: findings/poc/DF-2349/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-2349 · 5 files

File	Type	Description	Size
VERDICT.md	verdict	analysis: code bug confirmed, gate confirmed, fix authored	1.5 KB	↓ raw
fix.diff	suggested-fix	git-apply-able defense-in-depth fix (verified --check clean)	433 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

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DF-2349 — PoC verdict

File: sys/bus/u4b/uvc/uvc_ctrls.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)

uvc_ctrl_init_dev() iterates the per-unit bmControls bitmap with a uint8_t loop index i bounded by bCtrlSize*8. bCtrlSize is taken verbatim from the untrusted UVC descriptor; any bCtrlSize>=32 makes the bound>=256 so i wraps 255->0 and the loop never terminates, marching ctrl past the allocated topo_node->controls array (heap OOB write).

Cited lines

Why it does not reproduce on this guest

No USB webcam (UVC device) on the QEMU guest (usbconfig list shows no devices; no /dev/video*).

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

Defense-in-depth fix

Change the loop index from uint8_t to unsigned int so it cannot wrap at 256.

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-2349/fix.diff -> OK. No runtime test possible (HW/ACPI/device-gated).

↓ fix.diffper-fix-DF-2349

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-2349/{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-2349/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): uvc_ctrls uint8_t loop index wraps at 256 -> infinite loop + heap OOB (no USB webcam). 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.