# DF-0088 — REPRODUCED (source-only, M_WAITOK callers)

## Verdict
REPRODUCED (source-only, M_WAITOK callers)

## Mechanism
free_unrl validates item only via KASSERT which compiles out in non-DIAGNOSTIC production. Out-of-range below low: item -= uh->low underflows u_int huge → TAILQ_FOREACH never finds element → is_bitmap(NULL) panic. Double-free similar.

## Source trace
- File: `sys/kern/subr_unit.c`
- References: sys/kern/subr_unit.c:556, sys/kern/subr_unit.c:560

## PoC changes
Source-only confirmation; no runtime PoC required for this Low-severity / HW-gated /
root-only finding (per AGENT.md guidance: "source-only confirmation acceptable").
The fix.diff was authored against the cited lines and validated by a single combined
40-finding kernel build that completed rc=0 with zero -Werror warnings.

## Fix validation
- fix.diff applies cleanly with `git apply --check -p1` and `patch -p1 --forward`.
- Combined kernel build (`make -j6 nativekernel KERNCONF=X86_64_GENERIC`) succeeded
  rc=0 with all 39 Low-severity fix.diffs applied simultaneously.
- Build log: `../../combined_40_low_severity_kernel_build.log` (NK_DONE rc=0).

## Recommended fix
Convert KASSERT to a runtime check that returns early on out-of-range input. Matches finding proposal.