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CVE-2026-93830

net: stmmac: xgmac2: disable RBUE in default RX interrupt mask PUBLISHED

Description (CNA)

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.

Affected (CNA)

Vendor / productVersions
Linux / Linuxaffected d6ddfacd95c79d43465d4a85dffb1c9beca343a9 before 8c9d57b5dc098b84631d0b3559c84c499ea2170a; affected d6ddfacd95c79d43465d4a85dffb1c9beca343a9 before 7a10e54e42a8f73a8d731f5a281fc06bb41b9250; affected d6ddfacd95c79d43465d4a85dffb1c9beca343a9 before 6b3b91433d5f4eae6865cdaa96f40cd67849e1f6; affected d6ddfacd95c79d43465d4a85dffb1c9beca343a9 before 74dbb85a6a254b5fc1f265a6cd61b2ba9d9221d7; affected d6ddfacd95c79d43465d4a85dffb1c9beca343a9 before 0b1a5d3647ce07c27a9fffefc11a8cbf7d7b25ce; affected d6ddfacd95c79d43465d4a85dffb1c9beca343a9 before 87e2826ed2058747ddf014c082569a46bfadd96b; affected d6ddfacd95c79d43465d4a85dffb1c9beca343a9 before d3265c19b35d036bba327b36b5366bee76b0157c
Linux / Linuxaffected 4.19; unaffected 0 before 4.19; unaffected 5.10.271 through 5.10.*; unaffected 5.15.222 through 5.15.*; unaffected 6.1.189 through 6.1.*; unaffected 6.6.158 through 6.6.*; unaffected 6.12.111 through 6.12.*; unaffected 6.18.53 through 6.18.*; unaffected 7.2 through *

CWE

No CWE identifiers supplied.

References