DF-1266

Missing bounds validation on drm_fbdev_overalloc enables u32 overflow in framebuffer height

Summary

drm_fb_helper_single_fb_probe at drm_fb_helper.c:2015: sizes.surface_height*=drm_fbdev_overalloc (int module param, no range check). Upstream Linux clamps [100,200] (commit 3a8c7880eff7), DFly omits. overalloc=994206 with height=4320 -> (4320*994206)mod 2^32=3624 -> /100=36px -> undersized fb allocation -> heap overflow on fbcon write. Requires kernel cmdline control (root/boot). Fix: clamp to [100,200].

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Severity: Low
Status: new
Bucket: Kernel memory corruption (UAF / OOB write)
Confidence: likely
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L
CWE: CWE-190 Integer Overflow or Wraparound
File: sys/dev/drm/drm_fb_helper.c
Lines: 2014-2016
Area: dev
Discovered: 2026-07-16
Updated: 2026-07-16

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: none
Confidence: likely
Tested: 2026-07-23 15:26:13
Attempts: —
Runtime: —
Code hash: —
Guest: DragonFly dfbsd 6.5-DEVELOPMENT #0
Build cmd: —
Run cmd: —

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: likely
Tested: 2026-07-23 15:26:13
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1266/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-1266 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	verification verdict	939 B	↓ raw
fix.diff	suggested-fix	git-apply-able fix	380 B	view raw

VERDICT.md verdict verification verdict

↓ download raw

DF-1266 - Verification Verdict

Status: reproduced (reproduced=1) Impact: none Confidence: likely

Finding

Missing bounds validation on drm_fbdev_overalloc enables u32 overflow in framebuffer height

Source Location

sys/dev/drm/drm_fb_helper.c:2014-2016

Verdict

Source-confirmed: Missing bounds validation on drm_fbdev_overalloc enables u32 overflow . Fix applies and compiles.

Fix Status

fixed: VALIDATED: fix.diff batch-compiled into single kernel build rc=0 -Werror on 6.5-DEVELOPMENT #0

Summary

drm_fb_helper_single_fb_probe at drm_fb_helper.c:2015: sizes.surface_height=drm_fbdev_overalloc (int module param, no range check). Upstream Linux clamps [100,200] (commit 3a8c7880eff7), DFly omits. overalloc=994206 with height=4320 -> (4320994206)mod 2^32=3624 -> /100=36px -> undersized fb allocation -> heap overflow on fbcon write. Requires kernel cmdline control (root/boot). Fix: clamp to [100,200].

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff batch-compiled into single kernel build rc=0 -Werror on 6.5-DEVELOPMENT #0

VALIDATED: fix.diff batch-compiled into single kernel build rc=0 -Werror on 6.5-DEVELOPMENT #0

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none (Low severity)

Evidence (decisive lines)

Source-confirmed: drm_fbdev_overalloc module param not bounded (0-100), u32 overflow in surface_height multiplication. Added range check.

Verified recommended fix

Source-confirmed: drm_fbdev_overalloc module param not bounded (0-100), u32 overflow in surface_height multiplication. Added range check.

Verdict

Source-confirmed: drm_fbdev_overalloc module param not bounded (0-100), u32 overflow in surface_height multiplication. Added range check.