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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2025-39684
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-09-05 18:15:45 UTC
Updated2026-05-12 13:17:04 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Problem Types: CWE-908

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected ed9eccbe8970f6eedc1b978c157caf1251a896d4 868a1b68dcd9f2805bb86aa64862402f785d8c4a git Not specified
CNA Linux Linux affected ed9eccbe8970f6eedc1b978c157caf1251a896d4 ff4a7c18799c7fe999fa56c5cf276e13866b8c1a git Not specified
CNA Linux Linux affected ed9eccbe8970f6eedc1b978c157caf1251a896d4 d84f6e77ebe3359394df32ecd97e0d76a25283dc git Not specified
CNA Linux Linux affected ed9eccbe8970f6eedc1b978c157caf1251a896d4 f3b0c9ec54736f3b8118f93a473d22e11ee65743 git Not specified
CNA Linux Linux affected ed9eccbe8970f6eedc1b978c157caf1251a896d4 aecf0d557ddd95ce68193a5ee1dc4c87415ff08a git Not specified
CNA Linux Linux affected ed9eccbe8970f6eedc1b978c157caf1251a896d4 3cd212e895ca2d58963fdc6422502b10dd3966bb git Not specified
CNA Linux Linux affected 2.6.29 Not specified
CNA Linux Linux unaffected 2.6.29 semver Not specified
CNA Linux Linux unaffected 5.15.190 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.149 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.103 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.44 6.12.* semver Not specified
CNA Linux Linux unaffected 6.16.4 6.16.* semver Not specified
CNA Linux Linux unaffected 6.17 * original_commit_for_fix Not specified
ADP Siemens SIMATIC CN 4100 affected V5.0 custom Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/868a1b68dcd9f2805bb86aa64862402f785d8c4a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
lists.debian.org/debian-lts-announce/2025/10/msg00008.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org Third Party Advisory
git.kernel.org/stable/c/d84f6e77ebe3359394df32ecd97e0d76a25283dc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/ff4a7c18799c7fe999fa56c5cf276e13866b8c1a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
cert-portal.siemens.com/productcert/html/ssa-032379.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/3cd212e895ca2d58963fdc6422502b10dd3966bb 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/f3b0c9ec54736f3b8118f93a473d22e11ee65743 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/aecf0d557ddd95ce68193a5ee1dc4c87415ff08a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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