CVE-2026-64134: ALSA: pcm: Don't setup bogus iov_iter for silencing

From: Greg Kroah-Hartman <[email protected]>

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

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

ALSA: pcm: Don't setup bogus iov_iter for silencing

At transition to the iov_iter for PCM data transfer, we blindly
applied the iov_iter setup also for silencing (i.e. data = NULL), and
it leads to a calculation of bogus iov_iter.  Fortunately this didn't
cause troubles on most of architectures but it goes wrong on RISC-V
now, causing a NULL dereference.

Handle the NULL data case to treat the silencing in interleaved_copy()
for addressing the bug above.  noninterleaved_copy() has already the
NULL data handling, so it doesn't need changes.

The Linux kernel CVE team has assigned CVE-2026-64134 to this issue.


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

	Issue introduced in 6.6 with commit cf393babb37a1679a1ec1d864df1090353465e23 and fixed in 6.6.142 with commit 41a766c647294842c9b17672449f8e011048cba9
	Issue introduced in 6.6 with commit cf393babb37a1679a1ec1d864df1090353465e23 and fixed in 6.12.92 with commit ce836587e594af39ff048d9b29dee0f5f10692c9
	Issue introduced in 6.6 with commit cf393babb37a1679a1ec1d864df1090353465e23 and fixed in 6.18.34 with commit feff0251386aa6bb180a0a1cf7c1f91ba868113d
	Issue introduced in 6.6 with commit cf393babb37a1679a1ec1d864df1090353465e23 and fixed in 7.0.11 with commit c9f6768515818d71bdfc20119a81f3332c53b9c6
	Issue introduced in 6.6 with commit cf393babb37a1679a1ec1d864df1090353465e23 and fixed in 7.1 with commit e4d3386b74fba8e01280484b67ee481ece00201e

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-2026-64134
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:
	sound/core/pcm_lib.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/41a766c647294842c9b17672449f8e011048cba9
	https://git.kernel.org/stable/c/ce836587e594af39ff048d9b29dee0f5f10692c9
	https://git.kernel.org/stable/c/feff0251386aa6bb180a0a1cf7c1f91ba868113d
	https://git.kernel.org/stable/c/c9f6768515818d71bdfc20119a81f3332c53b9c6
	https://git.kernel.org/stable/c/e4d3386b74fba8e01280484b67ee481ece00201e