CVE-2026-80886: serial: msm: Disable DMA for kernel console UART

CVE-2026-80886: serial: msm: Disable DMA for kernel console UART

[Greg Kroah-Hartman]

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

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

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

serial: msm: Disable DMA for kernel console UART

At the moment, concurrent writes from userspace and the kernel to the
console can trigger a race condition that results in an infinite loop of
the same messages printed over and over again. This is most likely to
happen during system startup or shutdown when the init system starts/stops
a large number of system services that interact with various kernel code.

When userspace writes to the TTY device, the driver initiates an
asynchronous DMA transfer and releases the port lock. At the same moment,
the kernel printk path might grab the port lock and re-configure the UART
controller for PIO, without waiting for the DMA operation to complete. It
seems like this collision results in zero progress being reported for the
DMA engine, so the same text is printed to the console over and over again.

For the kernel console, we want a reliable output path that will be
functional even during crashes etc. So rather than implementing complex
code to synchronize the kernel console write routines with the userspace
DMA write routines, simply disable DMA for the console UART instance.

Similar checks exist in many other serial drivers, e.g. 8250_port.c,
imx.c, sh-sci.c etc.

The Linux kernel CVE team has assigned CVE-2026-80886 to this issue.


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

	Issue introduced in 4.4 with commit 3a878c430fd6eb4f8587f9ebd187f773bf85d1d6 and fixed in 5.10.261 with commit f58e568dc308c8e13f7730c8de2da5ed514e540d
	Issue introduced in 4.4 with commit 3a878c430fd6eb4f8587f9ebd187f773bf85d1d6 and fixed in 5.15.212 with commit bb4296de5b538b575978c588cb3738ab8524d01a
	Issue introduced in 4.4 with commit 3a878c430fd6eb4f8587f9ebd187f773bf85d1d6 and fixed in 6.1.178 with commit 6acea62738ed4cae6746483026706a773b44dad7
	Issue introduced in 4.4 with commit 3a878c430fd6eb4f8587f9ebd187f773bf85d1d6 and fixed in 6.6.145 with commit abc1926c88c189e5d698b91ed6890e09ab5c321d
	Issue introduced in 4.4 with commit 3a878c430fd6eb4f8587f9ebd187f773bf85d1d6 and fixed in 6.12.97 with commit 2727744ccb5ca59090451451ee94f530b1be04a5
	Issue introduced in 4.4 with commit 3a878c430fd6eb4f8587f9ebd187f773bf85d1d6 and fixed in 6.18.40 with commit d354716245192de2d203f2b35f22ab8dc13595e2
	Issue introduced in 4.4 with commit 3a878c430fd6eb4f8587f9ebd187f773bf85d1d6 and fixed in 7.1.5 with commit e3b42e326f4f30efcdc90bad5f5ba37e1cd91a47
	Issue introduced in 4.4 with commit 3a878c430fd6eb4f8587f9ebd187f773bf85d1d6 and fixed in 7.2 with commit 22dd2777e6c180e1c945b00f6d18550979436324

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-2026-80886
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/tty/serial/msm_serial.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/f58e568dc308c8e13f7730c8de2da5ed514e540d
	https://git.kernel.org/stable/c/bb4296de5b538b575978c588cb3738ab8524d01a
	https://git.kernel.org/stable/c/6acea62738ed4cae6746483026706a773b44dad7
	https://git.kernel.org/stable/c/abc1926c88c189e5d698b91ed6890e09ab5c321d
	https://git.kernel.org/stable/c/2727744ccb5ca59090451451ee94f530b1be04a5
	https://git.kernel.org/stable/c/d354716245192de2d203f2b35f22ab8dc13595e2
	https://git.kernel.org/stable/c/e3b42e326f4f30efcdc90bad5f5ba37e1cd91a47
	https://git.kernel.org/stable/c/22dd2777e6c180e1c945b00f6d18550979436324