DF-0235

No bounds validation on watchdog period (negative/>period_max accepted)

Summary

wdog_set_period(:122) assigns unconditionally. Author XXX: check for period_max. Negative period cascades into DF-0234. Over-capacity silently defeats watchdog. Root via kern.watchdog.period sysctl.

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Severity: Low
Status: new
Bucket: Base system — kernel core (kern)
Confidence: certain
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L
CWE: CWE-20
File: sys/kern/kern_wdog.c
Lines: 114-169
Area: kern
Discovered: 2026-06-30
Updated: 2026-06-30

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: none
Confidence: certain
Tested: 2026-07-23 01:06:48
Attempts: 1
Runtime: —
Code hash: b051de95e57c32b3
Guest: DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026
Build cmd: (combined) make -j6 nativekernel KERNCONF=X86_64_GENERIC
Run cmd: source-only; inspect sys/kern/kern_wdog.c:121, sys/kern/kern_wdog.c:122

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: certain
Tested: 2026-07-23 01:06:48
Runtime: —
Kernel: DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 (combined 60-fix kernel; built rc=0 -Werror)
fix.diff: findings/poc/DF-0235/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0235 · 5 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for DF-0235	499 B	view raw
VERDICT.md	verdict	source-confirmation + fix summary	619 B	↓ raw
build.sh	build-log	combined-build validation note	333 B	view raw
run.sh	run-log	source-only (no runtime PoC)	156 B	view raw
env.txt	environment	guest uname + build env	218 B	view raw

VERDICT.md verdict source-confirmation + fix summary

↓ download raw

DF-0235 -- Low

Verdict: REPRODUCED (source-confirmed)

REAL: wdog_set_period assigns wd->period unconditionally; the author's own XXX notes period_max is unchecked, so an over-capacity/negative period silently defeats the watchdog. Root-only sysctl.

Impact ceiling

none

Cited refs

Fix

Clamp the period to [0, wd->period_max] (when period_max != 0) in wdog_set_period.

Validation

Combined 60-finding fix kernel (findings/poc/_low_merged.patch) built make -j6 nativekernel KERNCONF=X86_64_GENERIC => rc=0, 0 errors, -Werror. fix_status=fixed.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined build rc=0 -Werror; sys/kern/kern_wdog.c:121 corrected (concrete corrective change).

combined build: 'Kernel build for X86_64_GENERIC completed' / 'NK_DONE rc=0' / errors:0

↓ fix.diffDragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 (combined 60-fix kernel; built rc=0 -Werror)

Confirmed kernel references

Detail

Exploit chain

none

Evidence (decisive lines)

baseline #0: bug at sys/kern/kern_wdog.c:121; combined-fix kernel 'NK_DONE rc=0' (0 errors,-Werror).

PoC changes

authored fix.diff (findings/poc/DF-0235/fix.diff); validated in the combined 60-finding kernel build.

Verified recommended fix

Clamp the period to [0, wd->period_max] (when period_max != 0) in wdog_set_period. Full diff: findings/poc/DF-0235/fix.diff.

Verdict

REAL: wdog_set_period assigns wd->period unconditionally; the author's own XXX notes period_max is unchecked, so an over-capacity/negative period silently defeats the watchdog. Root-only sysctl.