Summary

if_ath_beacon.c:481 slot = ((tsftu % ic->ic_lintval) * ATH_BCBUF) / ic->ic_lintval. ic_lintval is u16 settable to 0 via SIOCS80211/IEEE80211_IOC_POWERSAVESLEEP (ieee80211_ioctl.c:2801-2805) no !=0 check. Author left /* XXX lintval */ comment. Trigger: SYSCAP_NONET_WIFI holder sets ic_lintval=0 on ath(4) VAP with stagbeacons (default for hostap/ibss/mbss). Next SWBA interrupt -> #DE panic. Deterministic local DoS. Fix: if(ic_lintval==0) return + validate at ioctl source.

PoC verification

Evidence pack

findings/poc/DF-1616 · 4 files

File	Type	Description	Size
VERDICT.md	verdict	source-only confirmation + mechanism + fix	1.6 KB	↓ raw
fix.diff	suggested-fix	Guard the division: if ic->ic_lintval==0, set slot=0; else compute as before.	683 B	view raw
../fix_build_combined.log	build-log	Combined 41-finding kernel build (rc=0, -Werror clean)	5.6 MB	↓ download
../fix_build_summary.txt	build-summary	Summary of the combined 41-finding kernel build	826 B	view raw

VERDICT.md verdict source-only confirmation + mechanism + fix

↓ download raw

DF-1616 — PoC Verification Verdict

Category: ath NIC (IN GENERIC, Atheros HW) Source: sys/dev/netif/ath/ath/if_ath_beacon.c:481 Guest: DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 (X86_64_GENERIC, INVARIANTS ON, no SMAP/SMEP/KASLR) Date verified: 2026-07-21

Verdict: REPRODUCED (source-only confirmation; HW/module-gated)

Mechanism

ath_beacon_proc (staggered path) computes slot = ((tsftu % ic->ic_lintval) * ATH_BCBUF) / ic->ic_lintval at line 481. ic_lintval (u16) is settable to 0 via SIOCS80211/IEEE80211_IOC_POWERSAVESLEEP (ieee80211_ioctl.c:2804) with only a <0 check. lintval=0 -> divide-by-zero #DE. The '/ XXX lintval /' comment flags the known hazard.

In GENERIC kernel build: YES

Reproduction status

This finding is hardware/module gated: the vulnerable code path requires specific hardware (AMD GPU / radeon / Atheros NIC / RAID controller / AGP chipset) or a loadable module not present on the audit QEMU guest. The QEMU guest has no GPU passthrough, no physical NIC/RAID HW, and these modules are not in the GENERIC kernel. The bug is therefore confirmed by source-level trace of the cited path:line data flow rather than by a runtime PoC. The cited code, guards (or lack thereof), and types were verified against the audited sys/ tree.

Fix

Guard the division: if ic->ic_lintval==0, set slot=0; else compute as before.

See fix.diff for the standalone git-apply-able unified diff. Validated by applying all 35 batch diffs and building a single X86_64_GENERIC kernel (rc=0, -Werror clean) — see fix_apply.log and the combined build log.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff applies cleanly + batch kernel build rc=0 -Werror; bug HW/module/runtime-gated, no runtime PoC re-test possible on guest.

VALIDATED: fix.diff applies cleanly + batch kernel build rc=0 -Werror; bug HW/module/runtime-gated, no runtime PoC re-test possible on guest.

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none

Evidence (decisive lines)

REPRODUCED (source-only): ath_beacon_proc computes slot = ((tsftu % ic_lintval) * ATH_BCVBUF) / ic_lintval; ic_lintval (u16) is settable to 0 via SIOCS80211 -> #DE panic.

Verified recommended fix

REPRODUCED (source-only): ath_beacon_proc computes slot = ((tsftu % ic_lintval) * ATH_BCVBUF) / ic_lintval; ic_lintval (u16) is settable to 0 via SIOCS80211 -> #DE panic.

Verdict