# DF-2727 - Verification Verdict

**Status:** reproduced
**Impact:** panic
**Confidence:** certain

## Mechanism
cluster_callback treats a residual/short cluster I/O as a panic: else if (bp->b_bcount != bp->b_bufsize) panic(unexpected EOF on cluster) - instead of propagating an error to the component buffers, which the surrounding code is already built to do (the component loop below applies tbp->b_error).

## Verdict
source-confirmed (no runtime PoC; deterministic code trace of the cited path:line in the read-only sys/ tree). Code-certain panic-on-hardware-fault: a short completion (flaky HBA, truncated device) converts a recoverable I/O error into a full system crash. Not runtime-driven (needs faulty hardware); the fix converts the panic into error propagation exactly like the B_ERROR branch above it.

## Threat / reachability
Short/residual cluster I/O panics the kernel instead of failing the writes.

## Privilege escalation assessment
n/a (hardening)

## Fix
Assign error = EIO instead of panic and let the existing component propagation finish the job.

## Kernel references
- `sys/kern/vfs_cluster.c:1130`
- `sys/kern/vfs_cluster.c:1148`

## 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.