GHSA-J349-5P3C-R8V4

Vulnerability from github – Published: 2025-09-05 18:31 – Updated: 2025-11-03 18:31
VLAI?
Details

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 to kmalloc_array() with kcalloc(), but it is not always necessary to clear the whole buffer.

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{
  "affected": [],
  "aliases": [
    "CVE-2025-39684"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-09-05T18:15:45Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ncomedi: Fix use of uninitialized memory in do_insn_ioctl() and do_insnlist_ioctl()\n\nsyzbot reports a KMSAN kernel-infoleak in `do_insn_ioctl()`.  A kernel\nbuffer is allocated to hold `insn-\u003en` samples (each of which is an\n`unsigned int`).  For some instruction types, `insn-\u003en` samples are\ncopied back to user-space, unless an error code is being returned.  The\nproblem is that not all the instruction handlers that need to return\ndata to userspace fill in the whole `insn-\u003en` samples, so that there is\nan information leak.  There is a similar syzbot report for\n`do_insnlist_ioctl()`, although it does not have a reproducer for it at\nthe time of writing.\n\nOne culprit is `insn_rw_emulate_bits()` which is used as the handler for\n`INSN_READ` or `INSN_WRITE` instructions for subdevices that do not have\na specific handler for that instruction, but do have an `INSN_BITS`\nhandler.  For `INSN_READ` it only fills in at most 1 sample, so if\n`insn-\u003en` is greater than 1, the remaining `insn-\u003en - 1` samples copied\nto userspace will be uninitialized kernel data.\n\nAnother culprit is `vm80xx_ai_insn_read()` in the \"vm80xx\" driver.  It\nnever returns an error, even if it fails to fill the buffer.\n\nFix it in `do_insn_ioctl()` and `do_insnlist_ioctl()` by making sure\nthat uninitialized parts of the allocated buffer are zeroed before\nhandling each instruction.\n\nThanks to Arnaud Lecomte for their fix to `do_insn_ioctl()`.  That fix\nreplaced the call to `kmalloc_array()` with `kcalloc()`, but it is not\nalways necessary to clear the whole buffer.",
  "id": "GHSA-j349-5p3c-r8v4",
  "modified": "2025-11-03T18:31:39Z",
  "published": "2025-09-05T18:31:26Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-39684"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3cd212e895ca2d58963fdc6422502b10dd3966bb"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/868a1b68dcd9f2805bb86aa64862402f785d8c4a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/aecf0d557ddd95ce68193a5ee1dc4c87415ff08a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d84f6e77ebe3359394df32ecd97e0d76a25283dc"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f3b0c9ec54736f3b8118f93a473d22e11ee65743"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ff4a7c18799c7fe999fa56c5cf276e13866b8c1a"
    },
    {
      "type": "WEB",
      "url": "https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}


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