# DF-2911 - verification verdict

Status: **reproduced** | reproduced: 1 | impact: denial_of_service | confidence: certain

Both directions reproduced live on a vn-backed scratch disk with DIOCSDINFO64. Control: with the stock label (d_bbase=4096) a pwrite at slice offset 0 returns EROFS (the ds_reserved label-area guard, subr_diskslice.c:227). (a) A label with d_bbase=0 (CRC recomputed) is ACCEPTED by l64_setdisklabel - no check bounds d_bbase - and the same pwrite then returns 512: the EROFS label-area protection is fully disabled and we overwrote the on-disk label area. (b) A label with d_bbase=d_pstop=1072676864 (whole slice reserved, unvalidated) is ACCEPTED and every write to the slice returns EROFS - whole-slice lockout via one label ioctl. FWRITE root/operator-gated; consistency/self-inflicted class, not a privilege boundary.

## Evidence pointers
df2911_run.log: control EROFS; bbase=0 accepted then pwrite=512 WRITE ACCEPTED BELOW LABEL; bbase=pstop accepted then EROFS everywhere

## Kernel references
- sys/kern/subr_disklabel64.c:278
- sys/kern/subr_disklabel64.c:296
- sys/kern/subr_disklabel64.c:526
- sys/kern/subr_diskslice.c:227

## PoC changes vs the filing sketch
had to recompute the label d_crc (crc32 over d_magic..d_partitions[n]) after editing - the kernel validates it before the sanity block

## Fix
recommendation: validate d_bbase <= d_total_size, d_pbase >= d_bbase, d_pbase <= d_pstop <= d_total_size, partition lower bound d_bbase

fix status: not_testable

fix compiled in fix-all kernel; label-rig A/B rerun not performed (kernel build time-boxed); the fixed validation rejects both crafted labels by construction

Guest: DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul  2 06:02:04 UTC 2026     root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC  x86_64

## 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.