# DF-3094 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

The claimed panic path is not reachable by geometry crafting on this guest, and the current code propagates FAT read errors correctly: (a) crafting BPB sectors-per-FAT=32767 on an 8MB image is rejected at mount (mount_msdos: Invalid argument - geometry validated); (b) with the mount-accepted original geometry, 300x64KB extending writes complete cleanly; (c) the cited chain in the current tree returns the bread error (fatentry, msdosfs_fat.c:495-498 returns after brelse on bread failure) and extendfile propagates fatentry errors. Demonstrating the claimed assert requires genuine device I/O failure (failing media) which the vn-backed rig cannot inject. Refuted as-written on this tree unless real I/O errors hit an assert elsewhere in the chain.

## Kernel references
- sys/vfs/msdosfs/msdosfs_fat.c:495
- sys/vfs/msdosfs/msdosfs_fat.c:400

## Fix
See fix.diff.

## 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.