DF-0456

NULL deref in rfcomm_session_complete: credit NULL check under #ifdef DIAGNOSTIC only, no guard on production

Summary

rfcomm_session_complete(:446-454): loops count times dequeuing credit from rs_credits. NULL check on credit(:448-453) wrapped in #ifdef DIAGNOSTIC — no guard on production builds. If L2CAP over-reports count vs outstanding credits, STAILQ_FIRST returns NULL, line :454 derefs credit->rc_dlc -> panic. Not directly remote-triggerable (requires L2CAP completion accounting bug) but defense-in-depth gap.

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Severity: Low
Status: new
Bucket: Base system — network stack
Confidence: likely
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U:C:N/I:N/A:H
CWE: CWE-690
File: sys/netbt/rfcomm_session.c
Lines: 446-454
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 04:51:48
Attempts: 1
Runtime: —
Code hash: 3c6633076d95552c
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 04:51:48
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-0456/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0456 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	743 B	↓ raw
fix.diff	suggested-fix	fix for null-deref bug	428 B	view raw

VERDICT.md verdict source verification verdict

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DF-0456 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: null-deref

Impact: dos

Source file: sys/netbt/rfcomm_session.c

Mechanism

CONFIRMED: rfcomm_session_complete NULL check on credit wrapped in #ifdef DIAGNOSTIC. No guard on production builds. STAILQ_FIRST returns NULL -> crash. Fix: remove #ifdef.

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/netbt/rfcomm_session.c:448.

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/netbt/rfcomm_session.c:448. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0456. No PoC binary (source-only verification).

Verified recommended fix

Remove #ifdef DIAGNOSTIC around NULL check. Matches finding proposal.

Verdict

CONFIRMED source-only: NULL check on credit wrapped in #ifdef DIAGNOSTIC. No guard in production.