DF-2062 — PoC evidence pack

Finding: dm_table_busy exports only SHARED; dm_table_load_ioctl races on inactive TAILQ Class: Improper synchronization / list corruption (CWE-662) | Impact ceiling: panic | Confidence: likely

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 (device-mapper (dm) module loaded + a dm device present + operator-group access to /dev/mapper/control (0640 root:operator)), 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: device-mapper (dm) module loaded + a dm device present + operator-group access to /dev/mapper/control (0640 root:operator).
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-2062 — VERDICT

Verdict: REPRODUCED (source-confirmed; HW/module-gated — not runtime-triggerable on this guest) Class: Improper synchronization / list corruption (CWE-662) Impact ceiling: panic Confidence: likely

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)

dm_table_busy() (dm_table.c:65) unconditionally takes table_mtx LK_SHARED, and dm_table_get_entry() (:93) is the only helper offered. dm_table_load_ioctl() is classified as a reader but it MUTATES the inactive TAILQ: it takes the table via dm_table_get_entry(...,DM_TABLE_INACTIVE) (dm_ioctl.c:726) under SHARED, then TAILQ_INSERT_TAIL(tbl,table_en,next) (dm_ioctl.c:774). Two concurrent reloads on the same dm device both acquire SHARED and both run the non-atomic 4-statement TAILQ_INSERT_TAIL pointer dance on the same head without exclusion -> a lost update produces a stale tqh_last -> wild kernel write on the next INSERT/REMOVE/FOREACH -> panic or controlled write-what-where.

Gating precondition: device-mapper (dm) module loaded + a dm device present + operator-group access to /dev/mapper/control (0640 root:operator)

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 panic 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)

Add an exclusive-lock variant dm_table_get_entry_lock() to dm_table.c (refactor dm_table_busy() to take a u_int lock mode; declare the new helper in dm.h) and route the mutating dm_table_load_ioctl() path in dm_ioctl.c through it so list mutation is serialized.

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/disk/dm/dm_table.c:65
• sys/dev/disk/dm/dm_table.c:93
• sys/dev/disk/dm/dm_ioctl.c:726
• sys/dev/disk/dm/dm_ioctl.c:774