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.

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	1.0 KB	↓ raw
build.sh	build-script	N/A (source-only)	65 B	view raw
run.sh	run-script	N/A (source-only)	89 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 status (batch validation)

Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest make -j6 nativekernel KERNCONF=X86_64_GENERIC completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.

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