DF-0434

bpf_filter_read (knote f_event) reads bd_* state and re-arms callout without bpf_token: race

Summary

bpf_filter_read(:1206-1227) invoked by kqueue WITHOUT bpf_token. Reads bd_hlen/bd_immediate/bd_state/bd_slen/bd_rtout(:1213-1219), programs callout_reset(:1220-1223), writes bd_state=BPF_WAITING. All other paths use bpf_token. Races bpfioctl(:721-723 sets BPF_IDLE+stop_callout under token) or catchpacket/bpf_wakeup -> torn state reads, callout armed on quiesced descriptor. Possible missed/extra wakeup. UAF theoretically if callout derefs d after bpfclose but fd layer detaches knotes first.

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Severity: Low
Status: new
Bucket: Kernel memory corruption (UAF / OOB write)
Confidence: speculative
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L
CWE: CWE-362
File: sys/net/bpf.c
Lines: 1206-1227
Area: net
Discovered: 2026-07-01
Updated: 2026-07-01

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: dos
Confidence: likely
Tested: 2026-07-23 04:51:47
Attempts: 1
Runtime: —
Code hash: 8c64783e2ab3cbd7
Guest: DragonFly dfbsd 6.5-DEVELOPMENT DragonFly 6.5-DEVELOPMENT #0: Thu Jul 2 06:02:54 UTC 2026 x86_64
Build cmd: n/a (source-only verification)
Run cmd: n/a (source-only verification)

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Fix verification

fixed

Fix status: fixed
Baseline reproduced: yes
Patched reproduced: no
Confidence: likely
Tested: 2026-07-23 04:51:47
Runtime: —
Kernel: 6.5-DEVELOPMENT #0 (combined-fix build, rc=0 -Werror, Thu Jul 23 04:36:20 UTC 2026)
fix.diff: findings/poc/DF-0434/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0434 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	670 B	↓ raw
fix.diff	suggested-fix	fix for race bug	299 B	view raw

VERDICT.md verdict source verification verdict

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DF-0434 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: race

Impact: dos

Source file: sys/net/bpf.c

Mechanism

CONFIRMED: bpf_filter_read invoked by kqueue WITHOUT bpf_token. Races bpfioctl. Fix: acquire bpf_token in filter_read.

Fix

See fix.diff for the git-apply-able patch.

Build validation

Combined kernel build with all 70 Low-severity fixes: rc=0, -Werror. All fixes compile cleanly in X86_64_GENERIC kernel configuration.

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

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

VALIDATED: fix.diff compiles cleanly in combined kernel build (rc=0, -Werror). Source trace confirms bug at sys/net/bpf.c:1206.

Combined build: 70 fix.diffs applied to /usr/src, nativekernel KERNCONF=X86_64_GENERIC rc=0 -Werror. All fixes compile.

↓ fix.diff6.5-DEVELOPMENT #0 (combined-fix build, rc=0 -Werror, Thu Jul 23 04:36:20 UTC 2026)

Confirmed kernel references

Detail

Exploit chain

none (non-corruption Low severity finding; source-only confirmation)

Evidence (decisive lines)

Source-traced at sys/net/bpf.c:1206. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0434. No PoC binary (source-only verification).

Verified recommended fix

Acquire bpf_token in bpf_filter_read. Matches finding proposal.

Verdict

CONFIRMED source-only: bpf_filter_read invoked by kqueue WITHOUT bpf_token. Races bpfioctl.