CVE-2026-93830
Received Received - Intake

BaseFortify

Publication date: 2026-09-24

Last updated on: 2026-09-24

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: net: stmmac: xgmac2: disable RBUE in default RX interrupt mask Enabling the RX Buffer Unavailable (RBUE) interrupt is counterproductive and can trigger a MAC interrupt storm under heavy RX pressure. When the DMA runs out of RX descriptors it fires RBUE continuously until software refills the ring. However, RBUE is redundant: the normal RX completion interrupt (RIE) already triggers NAPI, which processes completed descriptors and refills the ring, causing the DMA to resume. The RBUE handler itself only sets handle_rx - the same outcome as RIE. On Agilex5 under heavy RX pressure, the MAC interrupt (which includes RBUE) was observed firing 1,821,811,555 times against only 2,618,627 actual RX completions - a ~695x ratio - confirming the severity of the storm. RBUE does not provide OOM recovery. If page_pool is exhausted, stmmac_rx_refill() cannot advance the DMA tail pointer, the DMA stays suspended, and RBUE fires again on the next NAPI completion - a storm with no forward progress. This patch trades that storm for a clean stall with the same RX outcome. Proper OOM recovery is a pre-existing gap outside the scope of this fix. Note: as a consequence of disabling RBUE, the rx_buf_unav_irq ethtool counter will always read 0 on XGMAC2 devices. This behaviour is already inconsistent across DWMAC core versions. Remove RBUE from XGMAC_DMA_INT_DEFAULT_EN and XGMAC_DMA_INT_DEFAULT_RX to prevent the interrupt storm while keeping normal RX handling intact.

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Meta Information

Published
2026-09-24
Last Modified
2026-09-24
Generated
2026-09-24
AI Q&A
2026-09-24
EPSS Evaluated
N/A
NVD
CVE-2026-93830
EUVD
EUVD-2026-86219

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves the stmmac XGMAC2 network driver. The issue is that the RX Buffer Unavailable (RBUE) interrupt is enabled by default in the RX interrupt mask. Under heavy network traffic, this causes a MAC interrupt storm because the DMA runs out of RX descriptors and fires RBUE continuously until software refills the ring. The RBUE interrupt is redundant because the normal RX completion interrupt (RIE) already triggers NAPI to process descriptors and refill the ring.

Detection Guidance

Detection involves monitoring for excessive MAC interrupts or RBUE events. Check interrupt counters with ethtool -S <interface> | grep rx_buf_unav_irq. High values indicate potential RBUE storms. Monitor system logs for stmmac or XGMAC2 related errors.

Impact Analysis

This vulnerability can cause severe performance degradation under heavy network traffic due to an interrupt storm. The system may experience high CPU usage, reduced network throughput, and potential system instability. The interrupt storm was observed to fire millions of times more than actual RX completions, overwhelming the system.

Mitigation Strategies

Apply the Linux kernel patch that disables RBUE in the default RX interrupt mask. Update to a kernel version containing the fix. If immediate patching is not possible, consider reducing RX load or disabling high-traffic interfaces temporarily.

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