CVE-2026-43319: spi: spidev: fix lock inversion between spi_lock and buf_lock

CVE-2026-43319: spi: spidev: fix lock inversion between spi_lock and buf_lock

[Greg Kroah-Hartman]

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

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

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

spi: spidev: fix lock inversion between spi_lock and buf_lock

The spidev driver previously used two mutexes, spi_lock and buf_lock,
but acquired them in different orders depending on the code path:

  write()/read(): buf_lock -> spi_lock
  ioctl():       spi_lock -> buf_lock

This AB-BA locking pattern triggers lockdep warnings and can
cause real deadlocks:

  WARNING: possible circular locking dependency detected
  spidev_ioctl() -> mutex_lock(&spidev->buf_lock)
  spidev_sync_write() -> mutex_lock(&spidev->spi_lock)
  *** DEADLOCK ***

The issue is reproducible with a simple userspace program that
performs write() and SPI_IOC_WR_MAX_SPEED_HZ ioctl() calls from
separate threads on the same spidev file descriptor.

Fix this by simplifying the locking model and removing the lock
inversion entirely. spidev_sync() no longer performs any locking,
and all callers serialize access using spi_lock.

buf_lock is removed since its functionality is fully covered by
spi_lock, eliminating the possibility of lock ordering issues.

This removes the lock inversion and prevents deadlocks without
changing userspace ABI or behaviour.

The Linux kernel CVE team has assigned CVE-2026-43319 to this issue.


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

	Fixed in 6.12.75 with commit f8431b8672231d378b03176fe74c95adfd3522cf
	Fixed in 6.18.16 with commit e341e18215030af2136836b78508e0d798916df7
	Fixed in 6.19.6 with commit 41ccfac7d302968a4f32b5f7b012d066c5f5cdf8
	Fixed in 7.0 with commit 40534d19ed2afb880ecf202dab26a8e7a5808d16

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-2026-43319
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/spi/spidev.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/f8431b8672231d378b03176fe74c95adfd3522cf
	https://git.kernel.org/stable/c/e341e18215030af2136836b78508e0d798916df7
	https://git.kernel.org/stable/c/41ccfac7d302968a4f32b5f7b012d066c5f5cdf8
	https://git.kernel.org/stable/c/40534d19ed2afb880ecf202dab26a8e7a5808d16