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The\nproblem is that not all the instruction handlers that need to return\ndata to userspace fill in the whole `insn->n` 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->n` is greater than 1, the remaining `insn->n - 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.","state":"PUBLISHED","assigner":"Linux","published_at":"2025-09-05 18:15:45","updated_at":"2026-05-12 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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->n` samples (each of which is an\n`unsigned int`).  For some instruction types, `insn->n` 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->n` 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->n` is greater than 1, the remaining `insn->n - 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."}],"providerMetadata":{"dateUpdated":"2026-05-11T21:34:15.439Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/868a1b68dcd9f2805bb86aa64862402f785d8c4a"},{"url":"https://git.kernel.org/stable/c/ff4a7c18799c7fe999fa56c5cf276e13866b8c1a"},{"url":"https://git.kernel.org/stable/c/d84f6e77ebe3359394df32ecd97e0d76a25283dc"},{"url":"https://git.kernel.org/stable/c/f3b0c9ec54736f3b8118f93a473d22e11ee65743"},{"url":"https://git.kernel.org/stable/c/aecf0d557ddd95ce68193a5ee1dc4c87415ff08a"},{"url":"https://git.kernel.org/stable/c/3cd212e895ca2d58963fdc6422502b10dd3966bb"}],"title":"comedi: Fix use of uninitialized memory in do_insn_ioctl() and do_insnlist_ioctl()","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2025-39684","datePublished":"2025-09-05T17:20:50.827Z","dateReserved":"2025-04-16T07:20:57.113Z","dateUpdated":"2026-05-12T12:06:11.333Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2025-09-05 18:15:45","lastModifiedDate":"2026-05-12 13:17:04","problem_types":["CWE-908"],"metrics":{"cvssMetricV31":[{"source":"nvd@nist.gov","type":"Primary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","baseScore":5.5,"baseSeverity":"MEDIUM","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH"},"exploitabilityScore":1.8,"impactScore":3.6}]},"configurations":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.29","versionEndExcluding":"5.15.190","matchCriteriaId":"70E10630-7292-4897-AF36-D7AF74FE096A"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.16","versionEndExcluding":"6.1.149","matchCriteriaId":"FDBE8280-8983-4D2D-943D-2E6D0104E2D8"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.2","versionEndExcluding":"6.6.103","matchCriteriaId":"F2293654-7169-49B5-8D0D-EE51EF8B8E48"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"6.12.44","matchCriteriaId":"12351F24-1133-4775-960C-F2B47E81298B"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.13","versionEndExcluding":"6.16.4","matchCriteriaId":"AFC28995-B8C3-4B68-8CB6-78E792B6629D"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:6.17:rc1:*:*:*:*:*:*","matchCriteriaId":"327D22EF-390B-454C-BD31-2ED23C998A1C"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:6.17:rc2:*:*:*:*:*:*","matchCriteriaId":"C730CD9A-D969-4A8E-9522-162AAF7C0EE9"}]}]},{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*","matchCriteriaId":"FA6FEEC2-9F11-4643-8827-749718254FED"}]}]}]},"legacy_mitre":{"record":{"CveYear":"2025","CveId":"39684","Ordinal":"1","Title":"comedi: Fix use of uninitialized memory in do_insn_ioctl() and d","CVE":"CVE-2025-39684","Year":"2025"},"notes":[{"CveYear":"2025","CveId":"39684","Ordinal":"1","NoteData":"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->n` samples (each of which is an\n`unsigned int`).  For some instruction types, `insn->n` 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->n` 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->n` is greater than 1, the remaining `insn->n - 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.","Type":"Description","Title":"comedi: Fix use of uninitialized memory in do_insn_ioctl() and d"}]}}}