CVE-2026-64244: drivers/base/memory: set mem->altmap after successful device registration

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

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

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

drivers/base/memory: set mem->altmap after successful device registration

If __add_memory_block() fails at xa_store() (under memory pressure for
example), device_unregister() is called, which eventually triggers
memory_block_release() with mem->altmap still set, causing a
WARN_ON(mem->altmap).  This was triggered by modifying virtio-mem driver.

Fix this by delaying the assignment of mem->altmap until after
__add_memory_block() has succeeded.

The Linux kernel CVE team has assigned CVE-2026-64244 to this issue.


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

	Issue introduced in 6.6 with commit 1a8c64e110435e44e71bcd50a75663174b575f22 and fixed in 6.6.144 with commit 802e113cf120df7208e4c7e604950a85e87120a8
	Issue introduced in 6.6 with commit 1a8c64e110435e44e71bcd50a75663174b575f22 and fixed in 6.12.95 with commit 22dc0d042f02ce82aa61422ea5f232628bfd9e9c
	Issue introduced in 6.6 with commit 1a8c64e110435e44e71bcd50a75663174b575f22 and fixed in 6.18.37 with commit 6c25bf4e44a2b6a14332f952bba0974521f5b72d
	Issue introduced in 6.6 with commit 1a8c64e110435e44e71bcd50a75663174b575f22 and fixed in 7.0.14 with commit bc3dd82a0ffd488bb902f4c69c3d28fd4088d973
	Issue introduced in 6.6 with commit 1a8c64e110435e44e71bcd50a75663174b575f22 and fixed in 7.1.2 with commit 059ac6252a63edf1cea79bf30bd860a8c264b62c
	Issue introduced in 6.6 with commit 1a8c64e110435e44e71bcd50a75663174b575f22 and fixed in 7.2-rc1 with commit a2b8d7827f48ee54a686cb80e4a1d0ff954ec42a

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-2026-64244
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/base/memory.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/802e113cf120df7208e4c7e604950a85e87120a8
	https://git.kernel.org/stable/c/22dc0d042f02ce82aa61422ea5f232628bfd9e9c
	https://git.kernel.org/stable/c/6c25bf4e44a2b6a14332f952bba0974521f5b72d
	https://git.kernel.org/stable/c/bc3dd82a0ffd488bb902f4c69c3d28fd4088d973
	https://git.kernel.org/stable/c/059ac6252a63edf1cea79bf30bd860a8c264b62c
	https://git.kernel.org/stable/c/a2b8d7827f48ee54a686cb80e4a1d0ff954ec42a