{"id":"CVE-2026-99081","title":"bnxt_en: fix DMA mapping length for padded small packets","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nbnxt_en: fix DMA mapping length for padded small packets\n\nStefan Fleischmann reported Intel IOMMU DMA Read faults on BCM57412\nNetXtreme-E NICs when transmitting packets…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= c0c050c58d840994ba842ad1c338a98e7c12b764 < cf8530a25ae92c4493e2f22981ecb46f0b66f4c8","Linux >= c0c050c58d840994ba842ad1c338a98e7c12b764 < 2956aca14dd2977cd08bd2ccafae3beb8b84b268","Linux >= c0c050c58d840994ba842ad1c338a98e7c12b764 < fbd977e513971ccb4f0762a7f59eac500e474f89","Linux >= c0c050c58d840994ba842ad1c338a98e7c12b764 < 5213f65a9667d3dd85db2e6df8f2e0516290db34","Linux >= c0c050c58d840994ba842ad1c338a98e7c12b764 < a51d233ccd4889aadb71dace863525cc2b00271e","Linux 4.4"],"published":"2026-10-23","updated":"2026-10-24","sourceUpdated":"2026-10-24T14:10:22.790Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-99081","references":[{"url":"https://git.kernel.org/stable/c/cf8530a25ae92c4493e2f22981ecb46f0b66f4c8"},{"url":"https://git.kernel.org/stable/c/2956aca14dd2977cd08bd2ccafae3beb8b84b268"},{"url":"https://git.kernel.org/stable/c/fbd977e513971ccb4f0762a7f59eac500e474f89"},{"url":"https://git.kernel.org/stable/c/5213f65a9667d3dd85db2e6df8f2e0516290db34"},{"url":"https://git.kernel.org/stable/c/a51d233ccd4889aadb71dace863525cc2b00271e"}],"tags":["cve.org"],"epss":0.00209,"epssPercentile":0.10462,"ingestedAt":"2026-10-23T13:24:55.513Z","slug":"CVE-2026-99081","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nbnxt_en: fix DMA mapping length for padded small packets\n\nStefan Fleischmann reported Intel IOMMU DMA Read faults on BCM57412\nNetXtreme-E NICs when transmitting packets on VLAN/macvlan interfaces:\n\n  DMAR: [DMA Read NO_PASID] Request device [18:00.0] fault addr 0xfc499000\n        [fault reason 0x06] PTE Read access is not set\n  bnxt_en 0000:18:00.0 eno1np0: Abandoning msg {0xb4 0x41a} len: 0 due to firmware status: 0x2000001\n  ...\n  NETDEV WATCHDOG: eno1np0 (bnxt_en): transmit queue 0 timed out\n\nThe fault address (0xfc499000) is on an exact 4KB page boundary,\npointing to a DMA read buffer overrun.\n\nIn bnxt_start_xmit(), packets smaller than BNXT_MIN_PKT_SIZE (52 bytes),\nsuch as 42-byte untagged ARP frames, are padded:\n\n    if (length < BNXT_MIN_PKT_SIZE) {\n        pad = BNXT_MIN_PKT_SIZE - length;\n        if (skb_pad(skb, pad))\n            goto tx_kick_pending;\n        length = BNXT_MIN_PKT_SIZE;\n    }\n\n    mapping = dma_map_single(&pdev->dev, skb->data, len, DMA_TO_DEVICE);\n    ...\n    dma_unmap_len_set(tx_buf, len, len);\n\nHowever, 'len' was initialized earlier to skb_headlen(skb) (e.g. 42 bytes)\nand is left unadjusted after padding. Consequently, dma_map_single() and\ndma_unmap_len_set() map and track only 42 bytes.\n\nLater, the hardware TX buffer descriptor is programmed with the padded length:\n\n    txbd->tx_bd_len_flags_type =\n        cpu_to_le32(((len + pad) << TX_BD_LEN_SHIFT) | flags |\n                    TX_BD_FLAGS_PACKET_END);\n\nThe NIC DMA engine is thus instructed to read 52 bytes from a region where\nonly 42 bytes were DMA-mapped. If skb->data ends near the boundary of a 4KB\npage (within 'pad' bytes of the next page), the hardware DMA read overruns\ninto the unmapped adjacent page, triggering an IOMMU fault.\n\nThis issue was exposed after commit 447cbe95ebb9 (\"vlan: fix skb_under_panic\nand races when toggling HW VLAN offload\") because reserving extra VLAN\nheadroom rounded LL_RESERVED_SPACE from 48 up to 64 bytes, shifting skb->data\noffsets and potentially causing small frames to land right against page\nboundaries.\n\nFix this by using skb_put_padto(skb, BNXT_MIN_PKT_SIZE) in\nbnxt_start_xmit(), before skb_shinfo(skb)->nr_frags is sampled,\nbecause padding might linearize the skb.\nThis ensures skb->len and skb_headlen(skb) reflect the padded size so\nthat dma_map_single() maps the full buffer and the descriptor length is\nconsistent. This also removes the temporary 'pad' variable and masking logic.\n\nThe padding is done after the SW USO branch, otherwise\nbnxt_sw_udp_gso_xmit() would account the padding as UDP payload\nand send it in extra segments.\n\nNote that SW USO segments are still not padded: with IPv4, a segment\ncarrying less than 10 bytes of UDP payload (small gso_size, or a short\nlast segment) is sent as a frame shorter than BNXT_MIN_PKT_SIZE.\nThis is a separate issue, left for a followup patch.\n\n## Affected\n\n- `Linux >= c0c050c58d840994ba842ad1c338a98e7c12b764 < cf8530a25ae92c4493e2f22981ecb46f0b66f4c8`\n- `Linux >= c0c050c58d840994ba842ad1c338a98e7c12b764 < 2956aca14dd2977cd08bd2ccafae3beb8b84b268`\n- `Linux >= c0c050c58d840994ba842ad1c338a98e7c12b764 < fbd977e513971ccb4f0762a7f59eac500e474f89`\n- `Linux >= c0c050c58d840994ba842ad1c338a98e7c12b764 < 5213f65a9667d3dd85db2e6df8f2e0516290db34`\n- `Linux >= c0c050c58d840994ba842ad1c338a98e7c12b764 < a51d233ccd4889aadb71dace863525cc2b00271e`\n- `Linux 4.4`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[{"seq":228822,"id":"CVE-2026-99081","ts":1792854083519,"field":"cvss","old":null,"new":"7.5"},{"seq":228821,"id":"CVE-2026-99081","ts":1792854083519,"field":"severity","old":"none","new":"high"}]}