# DF-3135 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. Per the DF-3058 precedent (verified again on this snapshot): sys/vfs/dirfs/ has no Makefile, is not referenced by sys/conf/files, appears in no kernel config, and the filesystem cannot be instantiated on this non-vkernel guest. The defect itself is line-certain from source: dirfs_open_helper tests dn_type & VDIR bitwise, so VBLK(3)/VSOCK(6)/VFIFO(7) nodes (3&2, 6&2, 7&2 all nonzero) get O_DIRECTORY and can never be opened, while VCHR/VLNK take the plain-file path; intended test is equality. Fix authored; compile validation not possible for dead code.

## Kernel references
- sys/vfs/dirfs/dirfs_subr.c:583

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

## Fix

operator: dn_type & VDIR -> dn_type == VDIR

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: no Makefile, not in sys/conf/files)

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.