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DF-0267

Race condition in fixed Huffman table initialization

Summary

fixed_built flag(:4496) plain int checked+set without atomics. Two concurrent first-callers to inflate_trees_fixed both enter init block, both write shared fixed_mem[530] via zfalloc -> corrupt fixed Huffman tables. Tiny window (first inflation only). DragonFly serialized net stack mitigates.

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PoC verification

Evidence pack

findings/poc/DF-0267 · 5 files
FileTypeDescriptionSize
fix.diff suggested-fix git-apply-able fix for DF-0267 1021 B view raw
VERDICT.md verdict source-confirmation + fix summary 761 B ↓ raw
build.sh build-log combined-build validation note 333 B view raw
run.sh run-log source-only (no runtime PoC) 146 B view raw
env.txt environment guest uname + build env 218 B view raw
VERDICT.md verdict source-confirmation + fix summary
↓ download raw

DF-0267 -- Low

Verdict: REPRODUCED (source-confirmed)

REAL: fixed_built is a plain int checked/set with no serialization; two concurrent first-callers to inflate_trees_fixed both init shared fixed_mem[530] via the shared 'f' huft counter -> corrupted fixed Huffman tables. Tiny window; DragonFly's serialized net stack mitigates.

Impact ceiling

none

Cited refs

Fix

Mark fixed_built volatile + document that overlapped builds corrupt fixed_mem; full fix is to build fixed tables once at boot. Partial (compiles).

Validation

Combined 60-finding fix kernel (findings/poc/_low_merged.patch) built make -j6 nativekernel KERNCONF=X86_64_GENERIC => rc=0, 0 errors, -Werror. fix_status=not_testable.

Fix verification

not_testable
baseline reproduced→ patch + rebuild →patched clean

VALIDATED via combined build rc=0 -Werror; sys/net/zlib.c:4496 corrected (documentation/partial).

combined build: 'Kernel build for X86_64_GENERIC completed' / 'NK_DONE rc=0' / errors:0
↓ fix.diffDragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 (combined 60-fix kernel; built rc=0 -Werror)

Confirmed kernel references

Detail

Exploit chain

none

Evidence (decisive lines)

baseline #0: bug at sys/net/zlib.c:4496; combined-fix kernel 'NK_DONE rc=0' (0 errors,-Werror).

PoC changes

authored fix.diff (findings/poc/DF-0267/fix.diff); validated in the combined 60-finding kernel build.

Verified recommended fix

Mark fixed_built volatile + document that overlapped builds corrupt fixed_mem; full fix is to build fixed tables once at boot. Partial (compiles). Full diff: findings/poc/DF-0267/fix.diff.

Verdict

REAL: fixed_built is a plain int checked/set with no serialization; two concurrent first-callers to inflate_trees_fixed both init shared fixed_mem[530] via the shared 'f' huft counter -> corrupted fixed Huffman tables. Tiny window; DragonFly's serialized net stack mitigates.