{
 "finding_id": "DF-3217",
 "status": "reproduced",
 "reproduced": 1,
 "impact": "none",
 "confidence": "certain",
 "verdict": "Reproduced on the stock INVARIANTS guest with a real Linux mke2fs ext4 image (extents flag set, one file hello injected via debugfs): mount -t ext2fs succeeds (EXTENTS is in EXT2F_INCOMPAT_SUPP, ext2fs.h:332-337), then cat/dd/rm of /mnt/hello all fail with EINVAL - ext2_bmap dispatches IN_E4EXTENTS inodes to the ext4_bmapext stub (ext2_bmap.c:84-86 -> :107-111 return (EINVAL);); unlink likewise fails through ext2_ext_truncate. A successful mount of a stock ext4 filesystem is a trap: every regular file is unusable. Post-fix A/B on the F40FIX kernel: the same image is rejected at mount with extents listed as an unsupported optional feature. No memory-safety impact (consistent refusal on all paths).",
 "exploit_chain": "",
 "evidence": "VERDICT.md with path:line citations; run.log where a live demo exists; fix.diff",
 "kernel_refs": [
  "sys/vfs/ext2fs/ext2_bmap.c:84",
  "sys/vfs/ext2fs/ext2_bmap.c:111",
  "sys/vfs/ext2fs/ext2fs.h:332"
 ],
 "poc_changes": "image built on the host (mke2fs -t ext4 + debugfs write), 32MB",
 "attempts": 1,
 "guest_uname": "DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul  2 06:02:54 UTC 2026     root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC  x86_64",
 "runtime_sec": 20,
 "guest_dirty": 0,
 "build_cmd": "host: mke2fs -t ext4 + debugfs write (image ext4_3217.img); guest: sh trigger.sh",
 "run_cmd": "sh trigger.sh (stock kernel: mount succeeds + I/O EINVAL; F40FIX: mount rejected rc=71)",
 "code_hash": "e662fd002ac82036eb50d399ffb851b2121adf67939a7bef9b68ebffc97b9ee6",
 "notes": "",
 "recommended_fix": "remove EXT2F_INCOMPAT_EXTENTS from EXT2F_INCOMPAT_SUPP (mount-time refusal)",
 "fix_status": "fixed",
 "fix_verdict": "A/B complete: the ext4 image is now rejected at mount (rc=71, console lists extents as unsupported) instead of mounting and failing every I/O; plain ext2 and read-only ext3 still mount (regression clean)."
}