CVE-2026-90015 (GCVE-0-2026-90015)
Vulnerability from cvelistv5
Published
2026-09-16 10:33
Modified
2026-10-19 08:56
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: xhci: fix lost bounce buffers on TDs spanning several ring segments When a TD reaches a link TRB with data that is not aligned to the endpoint's wMaxPacketSize, xhci_align_td() stages the unalignable tail through the bounce buffer of the ring segment holding that link TRB. xhci_unmap_td_bounce_buffer() later unmaps it and, for IN transfers, copies the data back into the URB's buffer. The enqueue path records the segment that was bounced in td->bounce_seg, under the assumption that a TD never spans more than two ring segments. That assumption does not hold: a TD large enough to span three or more segments crosses several link TRBs and can be bounced at each of them. Only the last one survives in td->bounce_seg, so every earlier bounce buffer is neither copied back nor DMA unmapped. The URB still completes with actual_length equal to the requested length and no error, so the transfer looks successful while a wMaxPacketSize sized hole in the destination buffer silently keeps its previous contents. It also leaks a DMA mapping per dropped bounce. Any sufficiently large and fragmented bulk transfer can hit this. It was found with a USB mass storage device behind xHCI backing a dm-verity target with 512 byte hash blocks, where the stale data is detected rather than silently consumed. The device enumerates as SuperSpeed, so wMaxPacketSize is 1024, while dm-bufio issues one 512 byte bio per hash block. verity_prefetch_io() makes the block layer merge hundreds of them into a single request of up to 512 scatterlist entries of 512 bytes each. At 256 TRBs per ring segment such a TD spans three segments, and every segment boundary falls on an odd multiple of 512, i.e. unaligned to wMaxPacketSize. dm-bufio then caches a hash block holding stale data and dm-verity declares the metadata block corrupted: device-mapper: verity: 8:2: metadata block 10850 is corrupted A reproducer running this under qemu is available at https://github.com/baloo/xhci-verity The bounce state (bounce_buf, bounce_dma, bounce_len, bounce_offs) already lives on the ring segment, so there is nothing extra to track. Keep recording the last bounced segment in td->bounce_seg and, on completion, walk the segments from td->start_seg up to it, unmapping every segment that still has a pending bounce. Stopping at td->bounce_seg rather than td->end_seg matters: a bounce implies the TD continues past that segment's link TRB, so bounce_seg is always strictly before end_seg, and a later TD may already have started in end_seg and been bounced there. Walking that far would copy a foreign bounce buffer into this URB and unmap it twice. It also keeps the walk correct if a TD ever wraps the whole ring so that end_seg == start_seg. [mn: Add ring->num_segs check to prevent unlikely infinite for loop.]
References
Impacted products
Vendor Product Version
Linux Linux Version: f9c589e142d04b8a19eb382162f804d17102b5ed
Version: f9c589e142d04b8a19eb382162f804d17102b5ed
Version: f9c589e142d04b8a19eb382162f804d17102b5ed
Version: f9c589e142d04b8a19eb382162f804d17102b5ed
Version: f9c589e142d04b8a19eb382162f804d17102b5ed
Version: f9c589e142d04b8a19eb382162f804d17102b5ed
Version: f9c589e142d04b8a19eb382162f804d17102b5ed
Version: f9c589e142d04b8a19eb382162f804d17102b5ed
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{
  "containers": {
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/usb/host/xhci-ring.c"
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              "versionType": "original_commit_for_fix"
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      ],
      "cpeApplicability": [
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nxhci: fix lost bounce buffers on TDs spanning several ring segments\n\nWhen a TD reaches a link TRB with data that is not aligned to the\nendpoint\u0027s wMaxPacketSize, xhci_align_td() stages the unalignable tail\nthrough the bounce buffer of the ring segment holding that link TRB.\nxhci_unmap_td_bounce_buffer() later unmaps it and, for IN transfers,\ncopies the data back into the URB\u0027s buffer.\n\nThe enqueue path records the segment that was bounced in td-\u003ebounce_seg,\nunder the assumption that a TD never spans more than two ring segments.\nThat assumption does not hold: a TD large enough to span three or more\nsegments crosses several link TRBs and can be bounced at each of them.\nOnly the last one survives in td-\u003ebounce_seg, so every earlier bounce\nbuffer is neither copied back nor DMA unmapped.\n\nThe URB still completes with actual_length equal to the requested length\nand no error, so the transfer looks successful while a wMaxPacketSize\nsized hole in the destination buffer silently keeps its previous\ncontents. It also leaks a DMA mapping per dropped bounce.\n\nAny sufficiently large and fragmented bulk transfer can hit this. It was\nfound with a USB mass storage device behind xHCI backing a dm-verity\ntarget with 512 byte hash blocks, where the stale data is detected rather\nthan silently consumed. The device enumerates as SuperSpeed, so\nwMaxPacketSize is 1024, while dm-bufio issues one 512 byte bio per hash\nblock. verity_prefetch_io() makes the block layer merge hundreds of them\ninto a single request of up to 512 scatterlist entries of 512 bytes each.\nAt 256 TRBs per ring segment such a TD spans three segments, and every\nsegment boundary falls on an odd multiple of 512, i.e. unaligned to\nwMaxPacketSize. dm-bufio then caches a hash block holding stale data and\ndm-verity declares the metadata block corrupted:\n\n  device-mapper: verity: 8:2: metadata block 10850 is corrupted\n\nA reproducer running this under qemu is available at\nhttps://github.com/baloo/xhci-verity\n\nThe bounce state (bounce_buf, bounce_dma, bounce_len, bounce_offs)\nalready lives on the ring segment, so there is nothing extra to track.\nKeep recording the last bounced segment in td-\u003ebounce_seg and, on\ncompletion, walk the segments from td-\u003estart_seg up to it, unmapping\nevery segment that still has a pending bounce.\n\nStopping at td-\u003ebounce_seg rather than td-\u003eend_seg matters: a bounce\nimplies the TD continues past that segment\u0027s link TRB, so bounce_seg is\nalways strictly before end_seg, and a later TD may already have started\nin end_seg and been bounced there. Walking that far would copy a foreign\nbounce buffer into this URB and unmap it twice. It also keeps the walk\ncorrect if a TD ever wraps the whole ring so that end_seg == start_seg.\n\n[mn: Add ring-\u003enum_segs check to prevent unlikely infinite for loop.]"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:56:28.983Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/c8124b28f12dbdd126118e63d0ebf8093a01fb81"
        },
        {
          "url": "https://git.kernel.org/stable/c/e04d5304a248e5d2a7f4faa87541644bdd320cfb"
        },
        {
          "url": "https://git.kernel.org/stable/c/a1629dfb011446d02905778f6df19f14c5f4f3b3"
        },
        {
          "url": "https://git.kernel.org/stable/c/43239fc6dfb62c50ae1b9c0e82bac0f8cd2e285c"
        },
        {
          "url": "https://git.kernel.org/stable/c/3c9a2b5a4f1183696f02ac280ced1d34afb409b1"
        },
        {
          "url": "https://git.kernel.org/stable/c/efaab8938fb92979be6df359f7d1a43fb7e4717d"
        },
        {
          "url": "https://git.kernel.org/stable/c/7236bbd2cb7d9fc0eda896bbd34790341e2a4377"
        },
        {
          "url": "https://git.kernel.org/stable/c/ff44dfb03a293bf30e31f98772a1dd316a6071d1"
        }
      ],
      "title": "xhci: fix lost bounce buffers on TDs spanning several ring segments",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-90015",
    "datePublished": "2026-09-16T10:33:21.471Z",
    "dateReserved": "2026-09-11T19:38:34.781Z",
    "dateUpdated": "2026-10-19T08:56:28.983Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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