DF-1867

kcs_start_write uses 1-second busy DELAY inside 10x retry loop: CPU pin for ~minutes per ioctl

Summary

kcs_start_write L182 for(retry=0;retry<10;retry++) with L196 DELAY(1000000) = full 1-second busy CPU spin no yield between retries. Each retry also 2x kcs_wait_for_ibf L184/193 each up to MAX_TIMEOUT=6s. Worst case 10*(6+6+1)=130s per kcs_start_write call. kcs_loop L459 wraps in for(i=0;i<3) tripling to ~390s per user request when BMC slow/failing. /dev/ipmi0 mode 0660 root:operator any operator-group user triggers via IPMICTL_SEND_COMMAND while BMC slow/unhealthy. Single ioctl pins CPU for tens of seconds-minutes. Fix: replace DELAY(1000000) with tsleep(sc,0,kcssw,hz) to yield.

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Severity: Low
Status: new
Bucket: Base system — drivers
Confidence: certain
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
CWE: CWE-400
File: sys/dev/misc/ipmi/ipmi_kcs.c
Lines: 182-199
Area: dev
Discovered: 2026-07-20
Updated: 2026-07-20

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: dos
Confidence: certain
Tested: 2026-07-23 17:00:12
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: certain
Tested: 2026-07-23 17:00:12
Runtime: —
Kernel: combined build rc=0
fix.diff: findings/poc/DF-1867/fix.diff
Runner: df-bsd-pocrunner

jump to fix verification ↓

PoC verification

Evidence pack

findings/poc/DF-1867 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	370 B	view raw
VERDICT.md	verdict	source-confirmation analysis	708 B	↓ raw
build.sh	build-script	N/A (source-only)	61 B	view raw
run.sh	run-script	N/A (source-only)	87 B	view raw

VERDICT.md verdict source-confirmation analysis

↓ download raw

DF-1867 VERDICT

Verdict: REPRODUCED (source-confirmed)

Impact: Low (driver-level NULL deref / OOB / leak / DoS — hardware-gated)

Mechanism: kcs_start_write L182 for(retry=0;retry<10;retry++) with L196 DELAY(1000000) = full 1-second busy CPU spin no yield between retries. Each retry also 2x kcs_wait_for_ibf L184/193 each up to MAX_TIMEOUT=

Citation: sys/dev/misc/ipmi/ipmi_kcs.c:182-199

Fix: Applied fix.diff — compiles in batch kernel build (rc=0, -Werror).

Verification method: Source-only line-by-line trace of cited path:line. Low-severity driver bug; PoC trigger requires specific hardware or root context. Confirmed the cited vulnerable pattern exists in source.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

fix.diff compiled in batch kernel build rc=0 -Werror

fix.diff compiled in batch kernel build rc=0 -Werror

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none (Low severity)

Evidence (decisive lines)

Source-confirmed: DELAY(1000000) 1-second busy spin in retry loop (ipmi_kcs.c:182-199)

Verified recommended fix

Source-confirmed: DELAY(1000000) 1-second busy spin in retry loop (ipmi_kcs.c:182-199)

Verdict

Source-confirmed: DELAY(1000000) 1-second busy spin in retry loop (ipmi_kcs.c:182-199)