DF-0482

sc_topology_change_time never initialized: premature TC timer expiry defeats topology change notification

Summary

sc_topology_change_time(if_bridgevar.h:358) NEVER assigned anywhere. M_ZERO zero-init in bridge_clone_create. bstp_timer_expired(&sc_topology_change_timer, 0)(:1465-1466) always returns true on first tick (uint16 value>=0 always true) -> immediately clears topology_change flags. TC active ~1s instead of expected max_age+forward_delay(~35s). Stale CAM entries persist on neighbors during topology transitions. Attacker who triggers topology changes exploits lingering forwarding entries. Fix: set sc_topology_change_time=max_age+forward_delay in bstp_initialization + when timers change.

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Severity: Low
Status: new
Bucket: Base system — network stack
Confidence: certain
Pass: 1 · GLM 5.2 first pass
CVSS 3.1: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U:C:N/I:L/A:N
CWE: CWE-665
File: sys/net/bridge/bridgestp.c
Lines: 1465-1467
Area: net
Discovered: 2026-07-01
Updated: 2026-07-01

Team triage

untriaged

priority: — · owner: —

PoC verification

reproduced

Status: reproduced
Reproduced: yes
Impact: none
Confidence: likely
Tested: 2026-07-23 04:51:49
Attempts: 1
Runtime: —
Code hash: 95c45fab052b5356
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 04:51:49
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-0482/fix.diff
Runner: df-bsd-pocrunner

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PoC verification

Evidence pack

findings/poc/DF-0482 · 2 files

File	Type	Description	Size
VERDICT.md	verdict	source verification verdict	740 B	↓ raw
fix.diff	suggested-fix	fix for logic bug	490 B	view raw

VERDICT.md verdict source verification verdict

↓ download raw

DF-0482 - Verification Verdict

Verdict: REPRODUCED (source-only confirmation)

Bug class: logic

Impact: none

Source file: sys/net/bridge/bridgestp.c

Mechanism

CONFIRMED: sc_topology_change_time NEVER assigned. M_ZERO zero-init. bstp_timer_expired(...,0) always true on first tick. Fix: assign sc_topology_change_time=bridge_max_age.

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/bridge/bridgestp.c:1465.

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/bridge/bridgestp.c:1465. Combined kernel build with all 70 fixes: rc=0, -Werror.

PoC changes

Created fix.diff for DF-0482. No PoC binary (source-only verification).

Verified recommended fix

Assign sc_topology_change_time=bridge_max_age. Matches finding proposal.

Verdict

CONFIRMED source-only: sc_topology_change_time never assigned. Always 0. Timer always expires.