# DF-2456 VERDICT

**Status:** reproduced
**Impact:** none
**Confidence:** certain

Production fdcpio moved 1020 bytes for FD_FORMAT with nsecs=255 (b_bcount = 4*255 computed at fdformat:2272 with no clamp to FD_MAX_NSEC=36): the first 144 bytes are the legal idfields region; the remaining 876 bytes were read from past the fd_formb heap object (kmalloc canary 0x66 delivered to the FDC data port starting exactly at stream index 144). Control nsecs=36 moved exactly 144 bytes with 0 past the object. The bytes are captured byte-by-byte at the emulated FDC data port - on the FDC_NODMA (YE PCMCIA) path they are physically transmitted; the read-back channel makes this a heap info-disclosure.

## Kernel references
- `sys/dev/disk/fd/fd.c:2272`
- `sys/dev/disk/fd/fd.c:1905`
- `sys/platform/pc64/include/ioctl_fd.h:58`

## Guest
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

## Notes
requires a floppy controller (FDC_NODMA path fully emulated; DMA path equivalent via isa_dmastart)

## 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.