Summary

kcs_polled_request L411 for(;;) loop only terminates when BMC transitions KCS to IDLE (state==2 break L418-419). No upper bound on iterations or elapsed time. kcs_read_byte L262-297 returns 1 (continue) as long as KCS_STATUS_STATE==KCS_STATUS_STATE_READ; BMC controls that state. Each sub-wait (kcs_wait_for_ibf/obf) individually bounded MAX_TIMEOUT(6s) but outer loop not. Hostile/compromised/buggy BMC keeps READ state forever -> kcs_loop kthread wedged indefinitely blocks all IPMI requests (watchdog keep-alive sensor reads user ioctls) and prevents module unload (ipmi_detach lksleep ipmi.c:895 waits forever). BMC trust boundary. Fix: cap outer loop with ticks-start>=MAX_TIMEOUT.

PoC verification

Evidence pack

findings/poc/DF-1865 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	556 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-1865 VERDICT

Verdict: REPRODUCED (source-confirmed)

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

Mechanism: kcs_polled_request L411 for(;;) loop only terminates when BMC transitions KCS to IDLE (state==2 break L418-419). No upper bound on iterations or elapsed time. kcs_read_byte L262-297 returns 1 (continu

Citation: sys/dev/misc/ipmi/ipmi_kcs.c:410-432

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: unbounded for(;;) in kcs_polled_request hangs on hostile BMC (ipmi_kcs.c:410-432)

Verified recommended fix

Source-confirmed: unbounded for(;;) in kcs_polled_request hangs on hostile BMC (ipmi_kcs.c:410-432)

Verdict