bcm.user Integrated Switch Fabric Driver Memory Buffer Ring Leak
The internal Broadcom switch fabric management daemon bcm.user on FG-100E/100F/200E appliances leaks DMA buffer descriptors under sustained L2 broadcast, multicast, or ARP traffic, consuming system memory until conserve mode locks management.
Technical Root Cause Analysis
On FortiGate appliances equipped with integrated Broadcom switch silicon (e.g. FG-100E, FG-100F, FG-200E), the user-space driver daemon bcm.user programs internal port VLAN memberships and polls hardware MAC address tables.
When networks encounter high broadcast frames (such as Windows NetBIOS, mDNS, or network scanning tools), the driver allocates packet descriptor rings in host system RAM to buffer packets destined for the control plane. In affected builds, a pointer reference leak prevents completed DMA buffers from being returned to the free pool, causing bcm.user to swell beyond 800MB–1.2GB.
Affected Firmware & Blast Radius Matrix
| FortiOS Branch | Vulnerable Builds | Confirmed Clean Build | Status & Workaround |
|---|---|---|---|
| FortiOS 7.0 | 7.0.0 – 7.0.13 | 7.0.14+ | Enable storm-control rate limiting |
| FortiOS 7.2 | 7.2.0 – 7.2.4 | 7.2.5+ | Upgrade recommended / prune broadcast |
| FortiOS 7.4 | Not Affected | 7.4.x Branch Clean | Updated Broadcom SDK v6.5 natively included |
Platform Impact: FG-100E, FG-101E, FG-100F, FG-101F, FG-200E, and FG-201E desktop and 1RU branch appliances.
Step 01: Free Verification CLI (Safe Read-Only)
Execute these commands to check bcm.user memory footprint and switch fabric DMA buffer counts:
Diagnostic Commands
# 1. Check bcm.user memory consumption
diagnose sys top-mem | grep bcm.user
# 2. Dump switch driver DMA ring buffer status
diagnose hardware switch bcm-user stat
# 3. Check switch MAC address table cache depth
diagnose switch-controller dump mac-cache
# 4. Inspect kernel socket buffer allocations
fnsysctl cat /proc/slabinfo | grep -E "kmalloc|skbuff"Remediation & Workaround Steps (Teaser Preview)
Access the complete storm control and driver stabilization guide in the Ferrite interactive platform:
Frequently Asked Questions
DMA buffer rings inside bcm.user fail to release packet descriptors when processing bursts of layer-2 broadcast and multicast traffic.
Only appliances with integrated Broadcom switch silicon, specifically FG-100E/F and FG-200E/F series.
Upgrade to FortiOS 7.0.14 or 7.2.5 which updates the Broadcom switch SDK driver with corrected ring deallocation.