FKIE_CVE-2025-39684

Vulnerability from fkie_nvd - Published: 2025-09-05 18:15 - Updated: 2025-11-03 18:16
Severity ?
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 to `kmalloc_array()` with `kcalloc()`, but it is not always necessary to clear the whole buffer.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/3cd212e895ca2d58963fdc6422502b10dd3966bb
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/868a1b68dcd9f2805bb86aa64862402f785d8c4a
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/aecf0d557ddd95ce68193a5ee1dc4c87415ff08a
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/d84f6e77ebe3359394df32ecd97e0d76a25283dc
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/f3b0c9ec54736f3b8118f93a473d22e11ee65743
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ff4a7c18799c7fe999fa56c5cf276e13866b8c1a
af854a3a-2127-422b-91ae-364da2661108https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
Impacted products
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{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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": "CVE-2025-39684",
  "lastModified": "2025-11-03T18:16:39.193",
  "metrics": {},
  "published": "2025-09-05T18:15:45.020",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/3cd212e895ca2d58963fdc6422502b10dd3966bb"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/868a1b68dcd9f2805bb86aa64862402f785d8c4a"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/aecf0d557ddd95ce68193a5ee1dc4c87415ff08a"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/d84f6e77ebe3359394df32ecd97e0d76a25283dc"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/f3b0c9ec54736f3b8118f93a473d22e11ee65743"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ff4a7c18799c7fe999fa56c5cf276e13866b8c1a"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "url": "https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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