comedi: Fix use of uninitialized memory in do_insn_ioctl() and do_insnlist_ioctl()

{
  "id": "febdb6b840e9e8dc76fe6dcdfb9102f98ce2cc77f23e12d2b527467cda666717",
  "url": "https://osv.dev/vulnerability/CVE-2025-39684",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "comedi: Fix use of uninitialized memory in do_insn_ioctl() and do_insnlist_ioctl()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: comedi: Fix use of uninitialized memory in do_insn_ioctl() and do_insnlist_ioctl() syzbot reports a KMSAN kernel-infoleak in `do_insn_ioctl()`. A kernel buffer is allocated to hold `insn->n` samples (each of which is an `unsigned int`). For some instruction types, `insn->n` samples are copied back to user-space, unless an error code is being returned. The problem is that not all the instruction handlers that need to return data to userspace fill in the whole `insn->n` samples, so that there is an information leak. There is a similar syzbot report for `do_insnlist_ioctl()`, although it does not have a reproducer for it at the time of writing. One culprit is `insn_rw_emulate_bits()` which is used as the handler for `INSN_READ` or `INSN_WRITE` instructions for subdevices that do not have a specific handler for that instruction, but do have an `INSN_BITS` handler. For `INSN_READ` it only fills in at most 1 sample, so if `insn->n` is greater than 1, the remaining `insn->n - 1` samples copied to userspace will be uninitialized kernel data. Another culprit is `vm80xx_ai_insn_read()` in the \"vm80xx\" driver. It never returns an error, even if it fails to fill the buffer. Fix it in `do_insn_ioctl()` and `do_insnlist_ioctl()` by making sure that uninitialized parts of the allocated buffer are zeroed before handling each instruction. Thanks to Arnaud Lecomte for their fix to `do_insn_ioctl()`. That fix replaced the call ",
    "evidence": "osv:CVE-2025-39684",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.15.190",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.149",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.103",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.44",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.16.4",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2025-39684",
      "aliases": [
        "CVE-2025-39684"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "ed9eccbe8970f6eedc1b978c157caf1251a896d4"
                },
                {
                  "fixed": "868a1b68dcd9f2805bb86aa64862402f785d8c4a"
                },
                {
                  "fixed": "ff4a7c18799c7fe999fa56c5cf276e13866b8c1a"
                },
                {
                  "fixed": "d84f6e77ebe3359394df32ecd97e0d76a25283dc"
                },
                {
                  "fixed": "f3b0c9ec54736f3b8118f93a473d22e11ee65743"
                },
                {
                  "fixed": "aecf0d557ddd95ce68193a5ee1dc4c87415ff08a"
                },
                {
                  "fixed": "3cd212e895ca2d58963fdc6422502b10dd3966bb"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39684.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "2.6.29"
                },
                {
                  "fixed": "5.15.190"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.16.0"
                },
                {
                  "fixed": "6.1.149"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
                  "fixed": "6.6.103"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.44"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.16.4"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39684.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:27.635910403Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-032379.html",
        "https://git.kernel.org/stable/c/3cd212e895ca2d58963fdc6422502b10dd3966bb",
        "https://git.kernel.org/stable/c/868a1b68dcd9f2805bb86aa64862402f785d8c4a",
        "https://git.kernel.org/stable/c/aecf0d557ddd95ce68193a5ee1dc4c87415ff08a",
        "https://git.kernel.org/stable/c/d84f6e77ebe3359394df32ecd97e0d76a25283dc",
        "https://git.kernel.org/stable/c/f3b0c9ec54736f3b8118f93a473d22e11ee65743",
        "https://git.kernel.org/stable/c/ff4a7c18799c7fe999fa56c5cf276e13866b8c1a",
        "https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39684.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-39684",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39684.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-39684",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 494413,
  "published_at": "2025-09-05T17:20:50.827+00:00"
}