CVE-2026-46281: vmalloc: fix buffer overflow in vrealloc_node_align()

CVE-2026-46281: vmalloc: fix buffer overflow in vrealloc_node_align()

[Greg Kroah-Hartman]

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

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

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

vmalloc: fix buffer overflow in vrealloc_node_align()

Commit 4c5d3365882d ("mm/vmalloc: allow to set node and align in
vrealloc") added the ability to force a new allocation if the current
pointer is on the wrong NUMA node, or if an alignment constraint is not
met, even if the user is shrinking the allocation.

On this path (need_realloc), the code allocates a new object of 'size'
bytes and then memcpy()s 'old_size' bytes into it.  If the request is to
shrink the object (size < old_size), this results in an out-of-bounds
write on the new buffer.

Fix this by bounding the copy length by the new allocation size.

The Linux kernel CVE team has assigned CVE-2026-46281 to this issue.


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

	Issue introduced in 6.18 with commit 4c5d3365882dbbc0784688784904f440d7a4c0f1 and fixed in 6.18.27 with commit e9b057a44deff4c59c13f44672a5cc74dcd57522
	Issue introduced in 6.18 with commit 4c5d3365882dbbc0784688784904f440d7a4c0f1 and fixed in 7.0.4 with commit b281adf71f786c325eb6d6d1582d4d05313438a8
	Issue introduced in 6.18 with commit 4c5d3365882dbbc0784688784904f440d7a4c0f1 and fixed in 7.1-rc2 with commit 82d1f01292d3f09bf063f829f8ab8de12b4280a1

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-2026-46281
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:
	mm/vmalloc.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/e9b057a44deff4c59c13f44672a5cc74dcd57522
	https://git.kernel.org/stable/c/b281adf71f786c325eb6d6d1582d4d05313438a8
	https://git.kernel.org/stable/c/82d1f01292d3f09bf063f829f8ab8de12b4280a1