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DF-0198

tag_types[tag_type] indexed without bounds check

Summary

devstat_end_transaction(:211-213) excludes DEVSTAT_TAG_NONE(==3) but no check >3 or <0. tag_types[3] array. Buggy driver passing 4/-1 -> adjacent field corruption (busy_time/start_time/flags). No current caller passes bad value.

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PoC verification

Evidence pack

findings/poc/DF-0198 · 5 files
FileTypeDescriptionSize
VERDICT.md verdict source-trace confirmation + fix rationale 1.5 KB ↓ raw
fix.diff suggested-fix git-apply-able fix for DF-0198 421 B view raw
build.sh build-script no-op (source-only finding) 78 B view raw
run.sh run-script no-op (source-only finding) 140 B view raw
env.txt environment guest uname, cc version 294 B view raw
VERDICT.md verdict source-trace confirmation + fix rationale
↓ download raw

DF-0198 — tag_types[tag_type] indexed without bounds check

Verdict: REPRODUCED (source-only confirmation, Low severity) Impact: none / defense-in-depth / latent (see below) Confidence: certain 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

Mechanism (source-traced)

CONFIRMED by source trace. devstat_end_transaction(:211-213) excludes DEVSTAT_TAG_NONE(==3) but no check >3 or <0. tag_types[3] array(:172). Buggy driver passing 4/-1 → adjacent field corruption. No current caller passes a bad value.

Kernel references (confirmed)

Fix

Bounds-check tag_type against nitems(tag_types). Supersedes finding proposal.

The standalone git-apply-able diff is in fix.diff.

Build validation

fix.diff was one of 50 diffs applied to a single combined make -j6 nativekernel KERNCONF=X86_64_GENERIC build on the audit guest (6.5-DEVELOPMENT #0, INVARIANTS ON). The combined build completed rc=0, 0 errors, 0 warnings under -Werror, confirming this fix (and all 49 others) compile cleanly together.

  • Combined build log (35649 lines): findings/poc/DF-0198/../../_combined_build.log (reference; full log at audit time).
  • Combined kernel.stripped sha256: 9337c4e114e3a91edc02fee6d9eff48799b3c0926c1151d642b4573cb7911000
  • Build completed: 2026-07-22T22:33:21Z

Fix verification

fixed
baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined build (rc=0).

NK_DONE rc=0; errors:0
↓ fix.diffDragonFly 6.5-DEVELOPMENT (50-diff combined; nativekernel rc=0)

Confirmed kernel references

Detail

Exploit chain

none — Low-severity source-only confirmation.

Evidence (decisive lines)

Source-trace confirmed at sys/kern/subr_devstat.c:211, sys/kern/subr_devstat.c:213, sys/sys/devicestat.h:172. Combined build rc=0.

PoC changes

Authored fix.diff in findings/poc/DF-0198/.

Verified recommended fix

Bounds-check tag_type against nitems(tag_types); supersedes finding proposal.

Verdict

CONFIRMED. devstat_end_transaction indexes tag_typestag_type no bounds check; array is [3]. Buggy driver passing 4/-1 -> adjacent field corruption.