{"id":"CVE-2025-39684","summary":"comedi: Fix use of uninitialized memory in do_insn_ioctl() and do_insnlist_ioctl()","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.","modified":"2026-03-20T12:43:00.360448Z","published":"2025-09-05T17:20:50.827Z","related":["MGASA-2025-0234","MGASA-2025-0235","SUSE-SU-2025:03600-1","SUSE-SU-2025:03634-1","SUSE-SU-2025:20851-1","SUSE-SU-2025:20861-1","SUSE-SU-2025:20870-1","SUSE-SU-2025:20898-1","SUSE-SU-2025:21074-1","SUSE-SU-2025:21139-1","SUSE-SU-2025:21179-1","SUSE-SU-2025:3751-1","SUSE-SU-2025:4057-1","SUSE-SU-2025:4132-1","SUSE-SU-2025:4141-1","openSUSE-SU-2025:20081-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39684.json"},"references":[{"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"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39684.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-39684"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"ed9eccbe8970f6eedc1b978c157caf1251a896d4"},{"fixed":"868a1b68dcd9f2805bb86aa64862402f785d8c4a"},{"fixed":"ff4a7c18799c7fe999fa56c5cf276e13866b8c1a"},{"fixed":"d84f6e77ebe3359394df32ecd97e0d76a25283dc"},{"fixed":"f3b0c9ec54736f3b8118f93a473d22e11ee65743"},{"fixed":"aecf0d557ddd95ce68193a5ee1dc4c87415ff08a"},{"fixed":"3cd212e895ca2d58963fdc6422502b10dd3966bb"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2025-39684.json"}}],"schema_version":"1.7.5"}