# DF-3219 verification

Kernel: DragonFly dfbsd 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64

## Bottom line

Not reproducible by construction: dirfs is dead code in this tree (DF-3058 precedent re-verified on this snapshot: no Makefile, absent from sys/conf/files, not loadable, and mount_dirfs refuses non-vkernel platforms). The defect is real in source: dirfs_root performs the dm_root lazy init completely unlocked (VFS_ROOT is not serialized by the VFS layer), so two concurrent path resolutions through the mountpoint both run the init, the loser leaks a dnp + host fd forever and can publish a root vnode without VROOT. Fix authored (serialize with dm_lock); compile validation impossible for dead code.

## Kernel references
- sys/vfs/dirfs/dirfs_vfsops.c:234-268

## Exploit chain
(none: availability/correctness finding; no privilege chain)

## Fix

serialize the lazy init with dm_lock

See fix.diff in this directory (git-apply-able against the read-only sys/
tree; applied only inside the disposable verification guest).

## Reproduction

build: n/a (dead code)

run: n/a

expected: n/a

## Notes on the PoC (what changed vs the finding sketch)

(none)

## 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.