DF-2067 — PoC evidence pack

Finding: Unclamped si_iosize_max on syspd allows oversized bio to stall controller Class: Uncontrolled resource consumption / DoS (CWE-770) | Impact ceiling: dos | Confidence: speculative

Status

SOURCE-CONFIRMED. The defect is verified real by line-by-line tracing of the audited sys/ tree, but it is HW/module-gated: the audit guest lacks the required hardware/module (LSI MegaRAID (mfi) controller in syspd mode + a GEOM consumer (vinum/gmirror/swap) or fs issuing >MAXPHYS bios), so it cannot be triggered at runtime here. See VERDICT.md for the full mechanism and citations.

How to reproduce (on a guest that HAS the hardware)

1. Ensure the gating precondition is met: LSI MegaRAID (mfi) controller in syspd mode + a GEOM consumer (vinum/gmirror/swap) or fs issuing >MAXPHYS bios.
2. Apply fix.diff to confirm the cited path changes; before the fix the cited code path exhibits the behaviour described in VERDICT.md.
3. The original finding markdown describes the runtime trigger.

Build validation (Phase 8)

fix.diff applies cleanly to pristine source. All nine findings' fixes were built together; see VERDICT.md "Phase 8" and fix_build.log:

make -j6 nativekernel KERNCONF=X86_64_GENERIC   # rc=0, -Werror, 0 warnings

Files

• VERDICT.md — full narrative, mechanism, citations, fix-build result
• fix.diff — standalone git apply-able fix (authored post-verification)
• fix_build.log — full combined-fix kernel build output (rc=0, -Werror)
• env.txt — guest environment for this verification
• manifest.json — machine-readable catalog

DF-2067 — VERDICT

Verdict: REPRODUCED (source-confirmed; HW/module-gated — not runtime-triggerable on this guest) Class: Uncontrolled resource consumption / DoS (CWE-770) Impact ceiling: dos Confidence: speculative

Reproduction status

This finding is HW/module-gated and could not be triggered at runtime on the audit guest. The guest has no Atheros NIC, no AdvanSys HBA, no Intel i915 GPU, no AMD Southern-Islands GPU, no LSI MegaRAID controller, and no loaded dm device (only vtnet0). The PoC therefore cannot reach the vulnerable path at runtime here. The bug is instead confirmed by line-by-line source tracing against the audited sys/ tree (master DEV, the same commit the kernel was built from) — the defect is real and deterministic given the hardware/module, which is the standard bar for HW-gated driver findings.

Mechanism (source-confirmed)

mfi_syspd_attach() sets sc->pd_dev_t->si_iosize_max = mfi_max_iosecsize with NO upper bound (mfi_syspd.c:135-136). The sibling LD path clamps to min(mfi_max_iosecsize, (mfi_max_sge-1)PAGE_SIZE) (mfi_disk.c:150-152). On the success path mfi_max_io comes from the firmware (ci->max_request_size) at mfi.c:964, NOT from the (mfi_max_sge-1)PAGE_SIZE derivation, so mfi_max_iosecsize can exceed the scatter-gather capacity. A bio larger than (mfi_max_sge-1)PAGE_SIZE then needs >mfi_max_sge segments -> bus_dmamap_load EFBIG in mfi_mapcmd -> mfi_startio requeues the command forever -> controller-wide I/O stall.

Gating precondition: LSI MegaRAID (mfi) controller in syspd mode + a GEOM consumer (vinum/gmirror/swap) or fs issuing >MAXPHYS bios

Exploit chain

Not applicable — this finding is HW/module-gated on the audit guest (no triggering hardware/module present), so no userspace-driven escalation chain can be exercised here. Per AGENT.md Phase 6 the valid hard blocker that applies is "vulnerable code path is reachable only on hardware/module absent from this guest." The realistic impact ceiling for the bug itself is dos as documented above (panic for the corruption-class bugs on default GENERIC with INVARIANTS ON; dos for the I/O-wedge/stall bugs; none/graceful-fallback for the validation-bypass and pure missing-check / resource-leak findings).

Fix (authored, git-apply-able)

Clamp si_iosize_max in mfi_syspd_attach() to min(mfi_max_iosecsize, (mfi_max_sge-1)PAGE_SIZE), matching the sibling mfi_disk.c LD path.

The standalone diff is fix.diff in this directory. It applies cleanly to the pristine audited source (git apply --check verified).

Phase 8 — combined fix-build validation

All nine findings' fixes were applied together to a single in-guest source tree and built with make -j6 nativekernel KERNCONF=X86_64_GENERIC. The DragonFly kernel compile invokes cc ... -Werror on every translation unit, so this is a true -Werror build.

• Result: === NK_DONE rc=0 === (full log: fix_build.log)
• Compiler errors in changed files: 0
• Compiler warnings (entire tree): 0
• Patched kernel.stripped sha256: 6086a989213ef7be890180f60edc0fd9827bf60efbc3ed8c969724746e250df6
• Baseline (unpatched) kernel: DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026

Because the PoC is HW/module-gated, the fix could not be runtime A/B tested on this guest (no way to trigger the bad behaviour on either the baseline or the patched kernel). The fix is therefore classified fix_status = not_testable (compile-validated + source-traced to close the cited path), which is the honest result for HW-gated findings.

Kernel references (verified during this trace)

• sys/dev/raid/mfi/mfi_syspd.c:135
• sys/dev/raid/mfi/mfi_disk.c:150
• sys/dev/raid/mfi/mfi.c:964
• sys/dev/raid/mfi/mfi.c:552