linux-cve-announce - CVE-2025-39686: comedi: Make insn_rw_emulate

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Message-ID: <2025090546-CVE-2025-39686-afb8@gregkh>
Date: Fri,  5 Sep 2025 19:21:00 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-39686: comedi: Make insn_rw_emulate_bits() do insn->n samples

From: Greg Kroah-Hartman <gregkh@...nel.org>

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.

The Linux kernel CVE team has assigned CVE-2025-39686 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 2.6.29 with commit ed9eccbe8970f6eedc1b978c157caf1251a896d4 and fixed in 5.15.190 with commit ab77e85bd3bc006ef40738f26f446a660813da44
	Issue introduced in 2.6.29 with commit ed9eccbe8970f6eedc1b978c157caf1251a896d4 and fixed in 6.1.149 with commit ae8bc1f07bcb31b8636420e03d1f9c3df6219a2b
	Issue introduced in 2.6.29 with commit ed9eccbe8970f6eedc1b978c157caf1251a896d4 and fixed in 6.6.103 with commit 842f307a1d115b24f2bcb2415c4e344f11f55930
	Issue introduced in 2.6.29 with commit ed9eccbe8970f6eedc1b978c157caf1251a896d4 and fixed in 6.12.44 with commit 92352ed2f9ac422181e381c2430c2d0dfb46faa0
	Issue introduced in 2.6.29 with commit ed9eccbe8970f6eedc1b978c157caf1251a896d4 and fixed in 6.16.4 with commit dc0a2f142d655700db43de90cb6abf141b73d908
	Issue introduced in 2.6.29 with commit ed9eccbe8970f6eedc1b978c157caf1251a896d4 and fixed in 6.17-rc3 with commit 7afba9221f70d4cbce0f417c558879cba0eb5e66

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-39686
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	drivers/comedi/drivers.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	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