{"id":"CVE-2026-93830","state":"PUBLISHED","title":"net: stmmac: xgmac2: disable RBUE in default RX interrupt mask","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: stmmac: xgmac2: disable RBUE in default RX interrupt mask\n\nEnabling the RX Buffer Unavailable (RBUE) interrupt is counterproductive\nand can trigger a MAC interrupt storm under heavy RX pressure. When the\nDMA runs out of RX descriptors it fires RBUE continuously until software\nrefills the ring.\n\nHowever, RBUE is redundant: the normal RX completion interrupt (RIE)\nalready triggers NAPI, which processes completed descriptors and refills\nthe ring, causing the DMA to resume. The RBUE handler itself only sets\nhandle_rx - the same outcome as RIE.\n\nOn Agilex5 under heavy RX pressure, the MAC interrupt (which includes\nRBUE) was observed firing 1,821,811,555 times against only 2,618,627\nactual RX completions - a ~695x ratio - confirming the severity of the\nstorm.\n\nRBUE does not provide OOM recovery. If page_pool is exhausted,\nstmmac_rx_refill() cannot advance the DMA tail pointer, the DMA stays\nsuspended, and RBUE fires again on the next NAPI completion - a storm\nwith no forward progress. This patch trades that storm for a clean\nstall with the same RX outcome. Proper OOM recovery is a pre-existing\ngap outside the scope of this fix.\n\nNote: as a consequence of disabling RBUE, the rx_buf_unav_irq ethtool\ncounter will always read 0 on XGMAC2 devices. This behaviour is already\ninconsistent across DWMAC core versions.\n\nRemove RBUE from XGMAC_DMA_INT_DEFAULT_EN and XGMAC_DMA_INT_DEFAULT_RX\nto prevent the interrupt storm while keeping normal RX handling intact.","publishedAt":"2026-09-24T16:03:12.818Z","updatedAt":"2026-10-03T10:58:00.189Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"8c9d57b5dc098b84631d0b3559c84c499ea2170a","versionType":"git"},{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"7a10e54e42a8f73a8d731f5a281fc06bb41b9250","versionType":"git"},{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"6b3b91433d5f4eae6865cdaa96f40cd67849e1f6","versionType":"git"},{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"74dbb85a6a254b5fc1f265a6cd61b2ba9d9221d7","versionType":"git"},{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"0b1a5d3647ce07c27a9fffefc11a8cbf7d7b25ce","versionType":"git"},{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"87e2826ed2058747ddf014c082569a46bfadd96b","versionType":"git"},{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"d3265c19b35d036bba327b36b5366bee76b0157c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.19","versionType":"semver"},{"version":"5.10.271","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.222","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.53","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h"]}],"references":["https://git.kernel.org/stable/c/8c9d57b5dc098b84631d0b3559c84c499ea2170a","https://git.kernel.org/stable/c/7a10e54e42a8f73a8d731f5a281fc06bb41b9250","https://git.kernel.org/stable/c/6b3b91433d5f4eae6865cdaa96f40cd67849e1f6","https://git.kernel.org/stable/c/74dbb85a6a254b5fc1f265a6cd61b2ba9d9221d7","https://git.kernel.org/stable/c/0b1a5d3647ce07c27a9fffefc11a8cbf7d7b25ce","https://git.kernel.org/stable/c/87e2826ed2058747ddf014c082569a46bfadd96b","https://git.kernel.org/stable/c/d3265c19b35d036bba327b36b5366bee76b0157c"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:34.582Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/93xxx/CVE-2026-93830.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-93830","state":"PUBLISHED","datePublished":"2026-09-24T16:03:12.818Z","dateUpdated":"2026-10-03T10:58:00.189Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-18T17:59:28.793Z"},"containers":{"cna":{"title":"net: stmmac: xgmac2: disable RBUE in default RX interrupt mask","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: stmmac: xgmac2: disable RBUE in default RX interrupt mask\n\nEnabling the RX Buffer Unavailable (RBUE) interrupt is counterproductive\nand can trigger a MAC interrupt storm under heavy RX pressure. When the\nDMA runs out of RX descriptors it fires RBUE continuously until software\nrefills the ring.\n\nHowever, RBUE is redundant: the normal RX completion interrupt (RIE)\nalready triggers NAPI, which processes completed descriptors and refills\nthe ring, causing the DMA to resume. The RBUE handler itself only sets\nhandle_rx - the same outcome as RIE.\n\nOn Agilex5 under heavy RX pressure, the MAC interrupt (which includes\nRBUE) was observed firing 1,821,811,555 times against only 2,618,627\nactual RX completions - a ~695x ratio - confirming the severity of the\nstorm.\n\nRBUE does not provide OOM recovery. If page_pool is exhausted,\nstmmac_rx_refill() cannot advance the DMA tail pointer, the DMA stays\nsuspended, and RBUE fires again on the next NAPI completion - a storm\nwith no forward progress. This patch trades that storm for a clean\nstall with the same RX outcome. Proper OOM recovery is a pre-existing\ngap outside the scope of this fix.\n\nNote: as a consequence of disabling RBUE, the rx_buf_unav_irq ethtool\ncounter will always read 0 on XGMAC2 devices. This behaviour is already\ninconsistent across DWMAC core versions.\n\nRemove RBUE from XGMAC_DMA_INT_DEFAULT_EN and XGMAC_DMA_INT_DEFAULT_RX\nto prevent the interrupt storm while keeping normal RX handling intact."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"8c9d57b5dc098b84631d0b3559c84c499ea2170a","versionType":"git"},{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"7a10e54e42a8f73a8d731f5a281fc06bb41b9250","versionType":"git"},{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"6b3b91433d5f4eae6865cdaa96f40cd67849e1f6","versionType":"git"},{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"74dbb85a6a254b5fc1f265a6cd61b2ba9d9221d7","versionType":"git"},{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"0b1a5d3647ce07c27a9fffefc11a8cbf7d7b25ce","versionType":"git"},{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"87e2826ed2058747ddf014c082569a46bfadd96b","versionType":"git"},{"version":"d6ddfacd95c79d43465d4a85dffb1c9beca343a9","status":"affected","lessThan":"d3265c19b35d036bba327b36b5366bee76b0157c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.19","versionType":"semver"},{"version":"5.10.271","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.222","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.53","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h"]}],"references":[{"url":"https://git.kernel.org/stable/c/8c9d57b5dc098b84631d0b3559c84c499ea2170a"},{"url":"https://git.kernel.org/stable/c/7a10e54e42a8f73a8d731f5a281fc06bb41b9250"},{"url":"https://git.kernel.org/stable/c/6b3b91433d5f4eae6865cdaa96f40cd67849e1f6"},{"url":"https://git.kernel.org/stable/c/74dbb85a6a254b5fc1f265a6cd61b2ba9d9221d7"},{"url":"https://git.kernel.org/stable/c/0b1a5d3647ce07c27a9fffefc11a8cbf7d7b25ce"},{"url":"https://git.kernel.org/stable/c/87e2826ed2058747ddf014c082569a46bfadd96b"},{"url":"https://git.kernel.org/stable/c/d3265c19b35d036bba327b36b5366bee76b0157c"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - Inbound Ethernet frames (IPv4/IPv6 unicast to the host MAC) are DMA'd into the XGMAC2 RX ring; emptying it asserts XGMAC_RBU. With XGMAC_RBUE in XGMAC_DMA_INT_DEFAULT_RX, stmmac_interrupt/stmmac_msi_intr_rx → stmmac_napi_check → dwxgmac2_dma_interrupt runs. XGMAC2 is a 10G IP Ethernet MAC (Agilex5, Tegra MGBE, snps,dwxgmac).\nAC:L - A remote flood is enough: DMA_DEFAULT_RX_SIZE is 512, and Agilex5 under heavy RX already produced 1,821,811,555 MAC IRQs versus 2,618,627 completions. The attacker sets arrival rate; no race or layout is required. The worse stall (page_pool_alloc_pages failure in stmmac_rx_refill) is also GFP_ATOMIC exhaustion from that flood.\nPR:N - dwxgmac2_dma_interrupt runs from the XGMAC DMA hardirq (stmmac_interrupt or stmmac_msi_intr_rx) on received frames before any socket, netfilter verdict, or authentication check.\nUI:N - The attacker sends the frames themselves; stmmac_interrupt/stmmac_msi_intr_rx schedules NAPI via stmmac_napi_check with no local user action.\nS:U - The RBUE storm runs in the host kernel ISR/NAPI (stmmac_interrupt, dwxgmac2_dma_interrupt, stmmac_napi_poll_rx); it does not cross a VM, IOMMU, or sandbox boundary.\nC:N - On XGMAC_RBU, dwxgmac2_dma_interrupt only increments x->rx_buf_unav_irq and returns handle_rx so NAPI runs; it does not read or return kernel memory to the sender.\nI:N - The RBU handler does not write attacker-controlled data into kernel objects; it only sets handle_rx. There is no OOB write, UAF, or control-flow hijack.\nA:H - With XGMAC_RBUE armed, RBU reasserts until stmmac_rx_refill advances the RX tail; if page_pool_alloc_pages fails, stmmac_napi_poll_rx's napi_complete_done path calls dwxgmac2_enable_dma_irq and the IRQ storms with no forward progress (~695x on Agilex5), livelocking the CPU."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-03T10:58:00.189Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"5.10.271"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"5.15.222"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.1.189"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.6.158"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.12.111"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.18.53"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}