linux-cve-announce - CVE-2025-38480: comedi: Fix use of uninitialized data in insn_rw_emulate

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Message-ID: <2025072814-CVE-2025-38480-d8ab@gregkh>
Date: Mon, 28 Jul 2025 13:22:22 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38480: comedi: Fix use of uninitialized data in insn_rw_emulate_bits()

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

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

comedi: Fix use of uninitialized data in insn_rw_emulate_bits()

For Comedi `INSN_READ` and `INSN_WRITE` instructions on "digital"
subdevices (subdevice types `COMEDI_SUBD_DI`, `COMEDI_SUBD_DO`, and
`COMEDI_SUBD_DIO`), it is common for the subdevice driver not to have
`insn_read` and `insn_write` handler functions, but to have an
`insn_bits` handler function for handling Comedi `INSN_BITS`
instructions.  In that case, the subdevice's `insn_read` and/or
`insn_write` function handler pointers are set to point to the
`insn_rw_emulate_bits()` function by `__comedi_device_postconfig()`.

For `INSN_WRITE`, `insn_rw_emulate_bits()` currently assumes that the
supplied `data[0]` value is a valid copy from user memory.  It will at
least exist because `do_insnlist_ioctl()` and `do_insn_ioctl()` in
"comedi_fops.c" ensure at lease `MIN_SAMPLES` (16) elements are
allocated.  However, if `insn->n` is 0 (which is allowable for
`INSN_READ` and `INSN_WRITE` instructions, then `data[0]` may contain
uninitialized data, and certainly contains invalid data, possibly from a
different instruction in the array of instructions handled by
`do_insnlist_ioctl()`.  This will result in an incorrect value being
written to the digital output channel (or to the digital input/output
channel if configured as an output), and may be reflected in the
internal saved state of the channel.

Fix it by returning 0 early if `insn->n` is 0, before reaching the code
that accesses `data[0]`.  Previously, the function always returned 1 on
success, but it is supposed to be the number of data samples actually
read or written up to `insn->n`, which is 0 in this case.

The Linux kernel CVE team has assigned CVE-2025-38480 to this issue.

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

	Issue introduced in 2.6.29 with commit ed9eccbe8970f6eedc1b978c157caf1251a896d4 and fixed in 6.1.147 with commit 3050d197d6bc9ef128944a70210f42d2430b3000
	Issue introduced in 2.6.29 with commit ed9eccbe8970f6eedc1b978c157caf1251a896d4 and fixed in 6.6.100 with commit 10f9024a8c824a41827fff1fefefb314c98e2c88
	Issue introduced in 2.6.29 with commit ed9eccbe8970f6eedc1b978c157caf1251a896d4 and fixed in 6.12.40 with commit 2af1e7d389c2619219171d23f5b96dbcbb7f9656
	Issue introduced in 2.6.29 with commit ed9eccbe8970f6eedc1b978c157caf1251a896d4 and fixed in 6.15.8 with commit 3ab55ffaaf75d0c7b68e332c1cdcc1b0e0044870
	Issue introduced in 2.6.29 with commit ed9eccbe8970f6eedc1b978c157caf1251a896d4 and fixed in 6.16 with commit e9cb26291d009243a4478a7ffb37b3a9175bfce9

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-2025-38480
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/3050d197d6bc9ef128944a70210f42d2430b3000
	https://git.kernel.org/stable/c/10f9024a8c824a41827fff1fefefb314c98e2c88
	https://git.kernel.org/stable/c/2af1e7d389c2619219171d23f5b96dbcbb7f9656
	https://git.kernel.org/stable/c/3ab55ffaaf75d0c7b68e332c1cdcc1b0e0044870
	https://git.kernel.org/stable/c/e9cb26291d009243a4478a7ffb37b3a9175bfce9