CVE-2026-74498: ALSA: usb-audio: Fix DMA buffer out-of-bounds write when fill_max is set

CVE-2026-74498: ALSA: usb-audio: Fix DMA buffer out-of-bounds write when fill_max is set

[Greg Kroah-Hartman]

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

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

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

ALSA: usb-audio: Fix DMA buffer out-of-bounds write when fill_max is set

When a USB audio endpoint requests full packet transfers via the fill_max
descriptor flag, data_ep_set_params() promotes ep->curpacksize to
ep->maxpacksize. However, maxsize is left at the original sample-rate
derived value.

Since u->buffer_size is allocated as maxsize * packets, the resulting
DMA buffer is far too small for the requested transfer length. When the
USB host controller streams up to curpacksize bytes per packet, it writes
past the end of the buffer via DMA, corrupting kernel heap memory.

Update maxsize to curpacksize when fill_max is set so that the allocated
DMA buffer size matches the actual transfer request size.

[ changed to reassign maxsize only when ep->fill_max is set -- tiwai ]

The Linux kernel CVE team has assigned CVE-2026-74498 to this issue.


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

	Issue introduced in 3.5 with commit 8fdff6a319e7dac757c558bd283dc4577e68cde7 and fixed in 6.6.151 with commit 3852974608f53e530e27c21d0c6c7d79c17b3f5a
	Issue introduced in 3.5 with commit 8fdff6a319e7dac757c558bd283dc4577e68cde7 and fixed in 6.12.103 with commit f9b6c9576568169139ac151f7881474f384659fd
	Issue introduced in 3.5 with commit 8fdff6a319e7dac757c558bd283dc4577e68cde7 and fixed in 6.18.44 with commit 04595233e5606d452f9f47e6989fc7ae7440fd40
	Issue introduced in 3.5 with commit 8fdff6a319e7dac757c558bd283dc4577e68cde7 and fixed in 7.1.8 with commit bd65b7191683bebd9923904f0558b9211b9129da
	Issue introduced in 3.5 with commit 8fdff6a319e7dac757c558bd283dc4577e68cde7 and fixed in 7.2-rc6 with commit d0199ae1666ff9ae2d1d568d64c3430d4c47f0e5

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-2026-74498
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/usb/endpoint.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/3852974608f53e530e27c21d0c6c7d79c17b3f5a
	https://git.kernel.org/stable/c/f9b6c9576568169139ac151f7881474f384659fd
	https://git.kernel.org/stable/c/04595233e5606d452f9f47e6989fc7ae7440fd40
	https://git.kernel.org/stable/c/bd65b7191683bebd9923904f0558b9211b9129da
	https://git.kernel.org/stable/c/d0199ae1666ff9ae2d1d568d64c3430d4c47f0e5