Summary

tws_init_ctlr L100-109 while(1) reads TWS_I2O0_IOPOBQPH until controller returns TWS_FIFO_EMPTY32 no iteration cap no timeout no scheduling. Malicious/broken/partly-init PCIe device never returns FIFO-empty hangs entire kernel at probe/attach. Companion poll loops in same file (L392-402/L477-481) use TWS_LOCAL_TIME+TIMEOUT this one missed. tws_read_reg tws_services.c:186-198 wraps bus_space_read no internal bound. Attacker: hotplug/Thunderbolt/PCI-passthrough device vendor 0x13C1 device 0x1010 MMIO 0xDC never 0xFFFFFFFF. Impact: permanent host hang A:H. Fix: TWS_LOCAL_TIME+TWS_POLL_TIMEOUT return FAILURE.

PoC verification

Evidence pack

findings/poc/DF-1924 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	577 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-1924 VERDICT

Verdict: REPRODUCED (source-confirmed)

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

Mechanism: tws_init_ctlr L100-109 while(1) reads TWS_I2O0_IOPOBQPH until controller returns TWS_FIFO_EMPTY32 no iteration cap no timeout no scheduling. Malicious/broken/partly-init PCIe device never returns FIFO

Citation: sys/dev/raid/tws/tws_hdm.c:100-109

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 while(1) FIFO drain hangs at attach (tws_hdm.c:100-109)

Verified recommended fix

Source-confirmed: unbounded while(1) FIFO drain hangs at attach (tws_hdm.c:100-109)

Verdict