Summary

SYSCTL_INT L114 _kern_dcons poll_hz CTLFLAG_RW NULL handler so generic sysctl_handle_int accepts any value including 0 (only SYSCAP_NOSYSCTL_WR enforced kern_sysctl.c:1446). dcons_timeout L353 and dcons_attach L512 both compute polltime=hz/poll_hz BEFORE the intended clamp if(polltime<1)polltime=1. Division evaluated before guard so poll_hz==0 -> integer divide-by-zero #DE on x86 -> kernel panic on next callout tick (within 10ms at default DCONS_POLL_HZ=100). Root trigger sysctlbyname(kern.dcons.poll_hz,&zero,...). Deterministic full-system DoS. No info leak no privilege gain. dcons need only be loaded kldload dcons or compiled in; dcons_crom FireWire attach not required dcons_attach unconditionally arms callout at MOD_LOAD. Fix: guard divisor before dividing if(poll_hz<1)poll_hz=1; or SYSCTL_PROC handler clamp writes to [1,hz].

PoC verification

Evidence pack

findings/poc/DF-1872 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	308 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-1872 VERDICT

Verdict: REPRODUCED (source-confirmed)

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

Mechanism: SYSCTL_INT L114 _kern_dcons poll_hz CTLFLAG_RW NULL handler so generic sysctl_handle_int accepts any value including 0 (only SYSCAP_NOSYSCTL_WR enforced kern_sysctl.c:1446). dcons_timeout L353 and dco

Citation: sys/dev/misc/dcons/dcons_os.c:353-512

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: hz/poll_hz div-by-zero when sysctl poll_hz=0 (dcons_os.c:353,512)

Verified recommended fix

Source-confirmed: hz/poll_hz div-by-zero when sysctl poll_hz=0 (dcons_os.c:353,512)

Verdict