CVE-2026-68178: misc: nsm: pin the module while the device is open

CVE-2026-68178: misc: nsm: pin the module while the device is open

[Greg Kroah-Hartman]

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

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

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

misc: nsm: pin the module while the device is open

misc_open() installs a misc driver's file operations with fops_get(),
which pins file_operations::owner before replacing the file's f_op.  The
NSM misc device leaves nsm_dev_fops.owner unset, so opening /dev/nsm does
not take a module reference on the nsm driver.

If the driver is built as a module, an open file descriptor can therefore
survive rmmod of the module that provides its ioctl callbacks.  A later
ioctl through that descriptor can call into unloaded module text.

Set nsm_dev_fops.owner to THIS_MODULE so the misc core holds the module
while any /dev/nsm file descriptor is open, matching the lifetime
expectation for the installed file operations.

The Linux kernel CVE team has assigned CVE-2026-68178 to this issue.


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

	Issue introduced in 6.8 with commit b9873755a6c8ccfce79094c4dce9efa3ecb1a749 and fixed in 6.12.101 with commit 1996639f824ce9468395cdb7bcb8f467fa787e77
	Issue introduced in 6.8 with commit b9873755a6c8ccfce79094c4dce9efa3ecb1a749 and fixed in 6.18.42 with commit 1da310b94504d42001e9c32c43c5dc105b777e5f
	Issue introduced in 6.8 with commit b9873755a6c8ccfce79094c4dce9efa3ecb1a749 and fixed in 7.1.6 with commit 9e9a82d00c3d10129fc310a7547b24a679d5d920
	Issue introduced in 6.8 with commit b9873755a6c8ccfce79094c4dce9efa3ecb1a749 and fixed in 7.2-rc5 with commit 3b231f1e9990f4c21220d0a69733ce2105891ff9

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-2026-68178
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/misc/nsm.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/1996639f824ce9468395cdb7bcb8f467fa787e77
	https://git.kernel.org/stable/c/1da310b94504d42001e9c32c43c5dc105b777e5f
	https://git.kernel.org/stable/c/9e9a82d00c3d10129fc310a7547b24a679d5d920
	https://git.kernel.org/stable/c/3b231f1e9990f4c21220d0a69733ce2105891ff9